No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
U/Pb and Pb/Pb zircon ages for arc-related intrusions of the Bolu Massif (W Pontides, NW Turkey): Evidence for Late Precambrian (Cadomian) age
Abstract
We present new U/Pb and Pb/Pb radiometric age data from two tectono-stratigraphic units of the regionally extensive Bolu Massif, in the W Pontides (İstanbul Fragment), N Turkey. A structurally lower unit (Sünnice Group) is cut by small meta-granitic intrusions, whereas the structurally higher unit comprises meta-volcanic rocks (Çaşurtepe Fm) cut by meta-granitic plutons (Tüllükiriş and Kapıkaya plutons). U/Pb single-crystal dating of zircons from the Kapıkaya Pluton yielded a concordant cluster, with a mean 238U/206Pb age of 565.3 ± 1.9 Ma. Zircons from the Tüllükiriş Pluton (affected by Pb loss) gave a 207Pb/206Pb age of 576 ± 6 Ma age (Late Precambrian). Small meta-granitic intrusions cutting the Sünnice Group yielded a less precise 207Pb/206Pb age of 262 ± 19 Ma (Early Permian). The older ages from the Bolu Massif confirm the existence of latest Precambrian arc magmatism related to subduction of a Cadomian ocean. We infer that the Bolu Massif represents a fragment of a Cadomian active margin. Cadomian orogenic units were dispersed as exotic terranes throughout the Variscan and Tethyan orogens, and the Bolu Massif probably reached its present position prior to latest Palaeozoic time. Our dating results also confirm that NW Turkey was affected by Hercynian magmatism related to subduction of Palaeotethys, as inferred for other areas of the Pontides.
... Most of Europe, Turkey, and Iran consist of continental blocks (e.g., Avalonia, Armorican Terrane Assemblage, Anatolide-Tauride Block) between the supercontinents Gondwana in the south and Laurentia and Baltica in the north ( Fig. 1) (e.g., Winchester et al., 2006;Linnemann et al., 2014;Ustaömer et al., 2005Ustaömer et al., , 2009Ustaömer et al., , 2011Ustaömer et al., , 2012aMoghadam et al., 2021;Žák et al., 2022). These continental blocks are separated by sutures, representing traces of the former oceanic basins. ...
... The Istanbul Zone has a late Neoproterozoic crystalline basement comprising metamorphic rocks intruded by granites ( Fig. 2) (Ustaömer and Rogers, 1999;Ustaömer et al., 2005;Chen et al., 2002;Yiğitbaş et al., 2004;Bozkurt et al., 2008Bozkurt et al., , 2013a. The basement rocks crop out mainly in the Bolu Massif and, to a lesser extent, in the Karadere Valley. ...
... Preliminary U-Pb zircon dating on one sample from the metavolcanic rocks yielded an igneous crystallization age of 606 ± 4 Ma (2σ) (Yılmazer et al., 2023). Previous U-Pb zircon ages from the Dirgine granitoid range from 565 to 576 Ma (Ustaömer et al., 2005;Bozkurt et al., 2013a), indicating that the protoliths of the metavolcanic and metapyroclastic rocks are ca. 30-40 Ma older than the batholith, and the low-grade metamorphism occurred before ca. ...
Avalonia, a large composite terrane, extends from the northeastern regions of America and Canada to southern Britain and Belgium/Netherlands, continuing on to Poland. It was accreted to Laurentia and Baltica during early Paleozoic. The late Neoproterozoic basement of the Istanbul Zone (NW Turkey), which is considered the far-east extension of Avalonia, is poorly known. This study deals with the petrology and age of the Dirgine Batholith, the largest component of the late Neoproterozoic basement. The batholith, ∼70 km long and ∼12 km wide, was emplaced into Neoproterozoic low-grade mafic to felsic metavolcanic and metapyroclastic rocks. Tonalite and
quartz diorite form the bulk of the batholith. Trondhjemite, granodiorite, and anorthositic gabbro occur in minor
amounts. Overall, rock types resemble low-Al tonalite-trondhjemite-granodiorite series and trondhjemites in ophiolite sequences. The batholith formed over a narrow time interval (562–574 Ma, late Ediacaran), as inferred by U–Pb zircon geochronology. In-situ Lu-Hf analyses of igneous zircons reveal a limited range of significantly positive initial εHf values (9.47 ± 1.46, 2σ) and young Hf depleted mantle model ages (0.78 ± 0.06 Ga), indicating the relatively juvenile character of original magmas. All rock types have typical subduction-related trace element signatures such as depletion in high-field-strength elements and enrichment in several fluid-mobile elements as well as nearly flat chondrite-normalized REE patterns. Geochemical characteristics indicate that crustal
assimilation was insignificant, and the batholith formed by fractional crystallization of mantle-derived low-K tholeiitic magmas involving mainly clinopyroxene, hornblende and ± plagioclase. The Dirgine Batholith and metamorphic country rocks probably represent the mid-crustal section of a late Neoproterozoic oceanic arc. The interpretation of an oceanic rather than continental arc is based on the significantly lower concentrations of incompatible
elements relative to continental arcs, nearly flat REE patterns of the rock types, and the juvenile nature of the primary magmas. These data, in concert with those in the literature, reveal that late Neoproterozoic oceanic arcs constitute an important component of far-east Avalonian terranes.
... An Ordovician to Upper Carboniferous continuous sedimentary succession, which unconformably overlies a latest Neoproterozoic crystalline basement, is a characteristic feature of the Istanbul Zone (Görür et al. 1997;Dean et al. 2000;Özgül 2012). Throughout most of the Palaeozoic era, the Istanbul Zone was located at the southern margin of Laurussia with no magmatic activity or metamorphism, and the latest Middle to Late Permian acidic intrusions represent the only known confirmed igneous event during the Palaeozoic in the Istanbul Zone (Yılmaz 1977;Ustaömer et al. 2005;Bozkurt et al. 2013aBozkurt et al. , 2013bOkay et al. 2013;Aysal et al. 2018). Even though the tectonic setting of this magmatism is still debated, there is a consensus on formation in an extensional setting via different mechanisms including (i) a rifting event after the Variscan orogeny (Seymen 1995;Okay and Nikishin 2015), (ii) a back-arc setting in response to the northward subduction of the Palaeo-Tethys during the Middle Permian -Early Triassic (Okay et al. 2006;Aysal et al. 2018), and (iii) a rift environment caused by transtensional faulting (Lom et al. 2016). ...
... It is separated from the Sakarya Zone in the south by the Intra-Pontide suture; in the west, the West Black Sea Fault separates the Istanbul Zone from the Strandja Zone ( Figure 1; Görür et al. 1997;Okay and Nikishin 2015). The crystalline basement of the zone is composed of latest Neoproterozoic metamorphic rocks intruded by calc-alkaline I-type granitoids with U-Pb zircon crystallization ages of 565-575 Ma, which are interpreted to have formed at the northern margin of Gondwana (Chen et al. 2002;Yiğitbaş et al. 2004;Ustaömer et al. 2005). This basement is unconformably overlain by a thick Ordovician-Carboniferous sedimentary succession, representing a passive continental margin sequence (Görür et al. 1997;Dean et al. 2000;Özgül 2012). ...
... Okay et al. 2011;Okay and Topuz 2017;Akdoğan et al. 2021). Following the orogeny, the deformed Palaeozoic sedimentary rocks are intruded by Permian granites, which represents the only confirmed Palaeozoic magmatic event in the Istanbul Zone (Yılmaz 1977;Ustaömer et al. 2005;Bozkurt et al. 2013aBozkurt et al. , 2013bOkay et al. 2013;Aysal et al. 2018). The bestknown example of these intrusions is the Late Permian Sancaktepe biotite-granite with a U-Pb zircon age of 254-257 Ma and a high-K calc-alkaline I-type composition ( Figure 1; Aysal et al. 2018). ...
The Istanbul Zone (NW Turkey) forms the eastward extension of Avalonia and was subjected to deformation, uplift and erosion for a time period of 40–50 Ma following the collision with the Sakarya Zone during Early to Late Carboniferous. This paper deals with the petrology and age of the volumetrically minor basic and acidic volcanism at the lowermost horizons of Middle Permian continental red beds, which are overlain by Lower Triassic marine sedimentary rocks in the Kocaeli Peninsula. The volcanic activity is represented mainly by amygdaloidal basalt, rhyolite and minor trachydacite. The amygdaloidal basalt was derived from near-primary middle-K calc-alkaline mantle melts with negligible crystal fractionation. On the other hand, the rhyolite and trachydacite compositionally resemble A2-type rhyolites and underwent low-pressure crystal fractionation as indicated by the presence of a significant Eu anomaly. Initial ɛNd values of amygdaloidal basalt range from 0.0 to 1.5 and those of rhyolite-trachydacite are between −0.4 and −3.4. Amygdaloidal basalt and rhyolite-trachydacite are not directly related to each other by crystal fractionation. Amygdaloidal basalt probably represents the product of the near-primary mantle melts from low-degree melting of a spinel peridotitic source, and the rhyolite-trachydacite originated from highly-fractionated products of basic magmas that are slightly more alkaline than amygdaloidal basalt. However, basic and intermediate products of alkaline basic magmas are unknown in this region to date. U-Pb dating of zircons from a rhyolite sample yielded an igneous crystallization age of 261 ± 3 Ma (2σ), suggesting that the date of deposition of the continental red beds goes back to the latest Middle Permian. Based on the transgressive nature of the Permian-Triassic sequence that starts from the Middle Permian continental red beds and grades into Lower Triassic marine deposits, we suggest that the volcanism likely occurred in an extensional setting. This extension was concurrent with the northward subduction of the Palaeo-Tethys beneath the Sakarya and Istanbul zones after the Variscan orogeny. Therefore, the latest Middle to Late Permian volcanism might have occurred during the initial stage of a back-arc extensional setting.
... They represent the Avalonian arc and are intruded by arc-related granite (c. 576 Ma; Ustaömer et al. 2005). Early Cambrian granitic dykes intrude into the Yellice arc (c. ...
... 565-556 Ma) and the rift-deposits are cut by Late Ediacaran rift-related dykes (c. 552-549 Ma) (Ustaömer et al. 2005;Şen 2021a). It is that the deposition of sedimentary rocks started in the late Ediacaran during the Yellice arc rifting (Şen 2021a) (Fig. 3). ...
... The locations of the dykes are given on the map. Isotopic ages are from Ustaömer et al. (2005) and Şen (2021a) for Late Ediacaran intrusions and dykes, Yiğitbaş et al. (1999), Ay et al. (2003) and Bozkurt et al. (2013) for Early Cambrian dykes and Çele meta-ophiolite, Şen (2021b) for Late Devonian-Late Carboniferous dykes, Aysal et al. (2018) (5) using shaking table, magnetic separation and heavy liquids techniques. d A polished epoxy mount with thirty-eight hand-picked zircon grains was covered with carbon in a BALTEC-SCD-005 sputter coating device, to prevent charging under the electron beam. ...
The İstanbul-Zonguldak Tectonic Unit is an Amazonia-derived continental fragment added to Baltica during the middle Paleozoic, and represents Far East Avalonia. The soft-docking time of two continental blocks, thus the consumption of the Teisseyre-Tornquist Ocean, is poorly known. This paper reports biotite-bearing dacite and pyroxene-bearing basaltic andesite and dacite dykes of Ordovician igneous crystallization ages in the İstanbul-Zonguldak Tectonic Unit (NW Turkey). They have porphyritic to spherulitic textures. U-Pb dating on igneous zircons from arc- and syncollisional-related dykes yielded Ordovician ages of ca. 484.1 ± 2.5 Ma (2σ) and 444.4 ± 3.7 to 443.0 ± 2.1 Ma (2σ). They display calc-alkaline signatures and are noteworthy with subduction components, as deduced by the presence of marked negative Nb anomalies. Biotite-bearing dykes intruded to it in an arc setting whereas pyroxene-bearing dykes emplaced into it in a syncollisional setting. Besides, Middle-Late Ordovician granites (c. 464-446 Ma) intruding the high-grade metamorphic rocks, known as rift-related intrusions in previous studies, show calc-alkaline affinities and contain subduction components, and they formed in a volcanic arc. I suggest that Early-Late Ordovician magmatism is related to the Teisseyre-Tornquist Ocean subducting under Far East Avalonia, and Late Ordovician magmatism is associated with soft-docking between two continental blocks, thus the destruction of the Teisseyre-Tornquist Ocean. Overall, its suture in Far East Avalonia overlaps with the Vardar suture in Balkans, and it can be traced from İzmir to Söğüt in Anatolia and represents the missing part in Far East Avalonia.
... The Istanbul Zone has a Late Neoproterozoic granitic and metamorphic basement (Chen et al., 2002;Ustaömer et al., 2005). The basement comprises (i) medium-to high-grade metamorphic rocks consisting of quartzofeldspathic gneiss and amphibolite, (ii) disrupted metaophiolite consisting of amphibolite/metagabbro and metaperidotite, and (iii) meta-andesite to -rhyolite intercalated with metasedimentary rocks. ...
... The basement comprises (i) medium-to high-grade metamorphic rocks consisting of quartzofeldspathic gneiss and amphibolite, (ii) disrupted metaophiolite consisting of amphibolite/metagabbro and metaperidotite, and (iii) meta-andesite to -rhyolite intercalated with metasedimentary rocks. These metamorphic rocks are intruded by voluminous granites with U-Pb zircon ages of 565-576 Ma (Chen et al., 2002;Okay et al., 2008;Ustaömer & Rogers, 1999;Ustaömer et al., 2005;Yiğitbaş et al., 2004) (Figures 2 and 3). A continuous, > 5 km thick sedimentary succession of Ordovician to Carboniferous age unconformably overlies the crystalline basement (Dean et al., 2000;Özgül, 2012). ...
... On the basis of the presence of Carboniferous eclogites at the Fore Range Zone of the Greater Caucasus (Perchuk & Philippot, 1997;Somin, 2011), the HT-LP metamorphism is thought to have occurred during Gradstein et al. (2012). Isotopic ages are from Aysal et al. (2012Aysal et al. ( , 2018, Ballato et al. (2018), Bozkurt et al. (2012), Chen et al. (2002), Dokuz (2011), Dokuz et al. (2010, Kaygusuz et al. (2012Kaygusuz et al. ( , 2016, Nzegge (2008), Nzegge et al. (2006), Okay et al. (2008Okay et al. ( , 2013Okay et al. ( , 2015, Sunal (2012), Topuz et al. (2010Topuz et al. ( , 2020, Ustaömer et al. (2005), Ustaömer, , 10.1029/2021TC006824 5 of 18 early Carboniferous at the mid-lower crustal part of a magmatic arc (Okay & Topuz, 2017). All these basement units were unconformably overlain by Jurassic volcanic and volcaniclastic rocks Altıner et al., 1991;Genç & Tüysüz, 2010;Kandemir & Yılmaz, 2009;Şen, 2007). ...
The Intra‐Pontide Suture between the Istanbul and Sakarya zones was regarded debatably either as a Neotethyan Suture or a trace of the Rheic Suture in Turkey. Here, we present U‐Pb ages and Lu‐Hf isotopic compositions of detrital zircons from the Silurian to Triassic sandstones of the Istanbul Zone. Upper Silurian‐Lower Devonian sandstone is dominated by Mesoproterozoic zircons (1950–900 Ma), with subordinate peaks at the latest Neoproterozoic to Silurian (750–420 Ma) and mid‐Archean (2850–2750 Ma) confirming their Avalonian affinity. Detrital zircon ages from Carboniferous‐Triassic sandstones show major peaks at Carboniferous‐Early Permian (360–270 Ma) and Late Neoproterozoic–Cambrian (750–480 Ma) while Mesoproterozoic zircons are insignificant. The εHf(t) values of the detrital zircons exhibit a wide range from −21.3 to +11.7, and over 62% of zircon grains have negative values, largely coinciding with those of the Paleozoic igneous rocks in the Sakarya Zone. The Istanbul Zone is devoid of Carboniferous igneous and/or metamorphic rocks. Therefore, abundant Carboniferous zircons and the disappearance of the Mesoproterozoic zircons in the Carboniferous‐Triassic sandstones of the Istanbul Zone require juxtaposition with a continental domain similar to the Sakarya and Strandja zones, which are characterized by widespread Carboniferous magmatism. We suggest that the Intra‐Pontide Suture represents the trace of the Rheic Suture in Turkey, along which Avalonia and Armorica collided during the Early Carboniferous.
... The isotopic data suggest that the activity was a product of long-lived subduction-related magmatic arc in the active northern Gondwana margin (Cacas et al. 2014) in the Eastern Pyrenees and in the Bohemian Massif (Dörr et al. 2002;Soejono et al. 2016). This process was also an important crust-forming period for Turkey since the Cadomian arc-type basement units are widespread within the Sakarya Zone (Tunç et al. 2012;Yiğitbaş and Tunç 2020), the İstanbul Zone (Chen et al. 2002;Yiğitbaş et al. 2004;Ustaömer et al. 2005;Okay et al. 2008), the Anatolide-Tauride block (Abbo et al. 2015;Kröner and Şengör 1990;Gürsu et al. 2004;Bozkaya et al. 2006), the Bitlis and Pötürge Massifs (Ustaömer et al. 2009(Ustaömer et al. , 2012Gürsu et al. 2015;Beyarslan et al. 2016), the Istranca Massif (Yılmaz Şahin et al. 2014;Okay 2014;Natal'in et al. 2016), and the Menderes Massif (Bozkurt and Oberhänsli 2001;Candan et al. 2011). ...
... Previous studies identified and mapped the Late Neoproterozoic igneous rocks in the Bolu Massif and Karadere basement in the İstanbul Zone (Chen et al. 2002;Ustaömer et al. 2005;Okay et al. 2008). They also suggest an Avalonian origin for these igneous rocks displaying intrusive contact with metaclastics and metavolcanites. ...
... They also suggest an Avalonian origin for these igneous rocks displaying intrusive contact with metaclastics and metavolcanites. Zircon U-Pb crystallization ages from the plutons are between 565 and 576 Ma in the Bolu Massif (Ustaömer et al. 2005), and between 560 and 590 Ma in the Karadere basement (Chen et al. 2002). Similar ages were reported from metagranitoids of the Armutlu peninsula . ...
... On the other hand, similar Permo-Triassic magmatic units have been documented from the western Sakarya Composite Terrane ( Fig. 1a; e.g. Istrandja Massif, Okay et al. 2001;Sunal et al. 2006;Natal'in et al. 2016;Kazdag Massif, Ustaömer et al. 2016) and the Istanbul-Zonguldak Terrane (e.g., Bolu Massif, Ayda Ustaömer et al. 2005;Kürek Granitoid, Okay et al. 2013;Sancaktepe Pluton, Aysal et al. 2018), and these arc units may have been generated by northward subduction of this Paleozoic-early Mesozoic ocean along the southern Eurasia margin (for compilation of the age data, see Aysal et al. 2018). Moreover, proposed that the buried late Triassic magmatic arc in the Scythian Platform ( Fig. 1a; Tikhomirov et al. 2004) may have been formed above the low-angled northward subduction of a long-lived Tethys ocean. ...
... The Istanbul-Zonguldak Terrane comprises of a Neoproterozoic crystalline basement (e.g. Ayda Ustaömer et al. 2005) and a well-observed Paleozoic sequence (from the lower Ordovician to the upper Carboniferious; e.g. Okay et al. 2015 and references therein). ...
... It is well-known that the Permo-Triassic continental arc/back arc units are found in the Istanbul-Zonguldak Terrane (e.g. Ayda Ustaömer et al. 2005;Okay et al. 2013;Aysal et al. 2018) and western Sakarya Composite Terrane (e.g. Sunal et al. 2006;Okay et al. 2001;Natal'in et al. 2016;Ustaömer et al. 2016). ...
The tracing of Triassic arc magmatism is much-debated for a long time along the Sakarya Composite Terrane in Turkey and southern Black Sea region. The Dodurga Pluton is located in the Central Pontides (N Turkey), one of most complicated regions around the Black Sea region, and represents the first documented middle Triassic continental arc in the region. This pluton comprises of dacite porphyry and granodiorite, and displays calc-alkaline signatures, which is in agreement with arc-related and I-type magmas. The PM-normalized multi element and CN-normalized REE patterns are akin to volcanic arc granites, and characterized by LILEs and LREEs enrichments relative to HFSEs and HREEs coupled with negative Nb anomalies, which confirm derivation in a subduction-related tectonic setting. Moreover, the major and trace element systematics of the samples including higher Sr/Y ratios (22.93 to 101.36) and lower Yb contents (0.31 to 1.30 ppm) are consistent with those from adakitic melts compared to classical arc magmas. Therefore, this pluton also represents the first middle Triassic adakite-like magmatic occurrence in Turkey. Overall petrographic and geochemical signatures reported here indicate that the Dodurga Pluton might have been derived from a heterogeneous source, mixed by melts from subducted oceanic slab and lower continental crust in an active continental margin. Based on the Tethyan evolution in Anatolian realm, three geodynamic scenarios are possible for its formation, and it could have been formed as a result of northward or southward-subduction of the Paleotethys Ocean or northward-subduction of the northern branch of Neotethys Ocean during the middle Triassic.
Please click full-text view link below;
https://rdcu.be/b1ZwQ
... Namely, whilst the LC SMM has recently been illustrated as a Cadomian segment within a variety of palinspastic reconstructions (Himmerkus et al., 2007(Himmerkus et al., , 2009Meinhold et al., 2010;Kounov et al., 2012;Anti c et al., 2016), the Upper Complex due to extensive reworking (Zagorchev et al., 2015) during several tectonothermal episodes having no palaeocontinental record as yet. By applying detrital isotopic provenance analyses (cratonic erosion sources), the Avalonian delineation of the Cadomian segments within the Southern Carpathians (e.g., Iancu et al., 2005;Oczlon et al., 2007;Balintoni et al., 2010;Balintoni and Balica, 2013;Balintoni et al., 2014) and the Balkan-Hellenic-Eastern Mediterranean (e.g., Ustaömer et al., 2005Ustaömer et al., , 2011Zulauf et al., 2007;Meinhold et al., 2010;Kounov et al., 2012;Anti c et al., 2016) is hampered by the severe Alpine structural rearrangements and a predominant focus on the latter. Thus, the focal point and the aim of this review study is understanding the earliest Palaeozoic plate-tectonic behaviour including Variscan accretion of the outboard SMM (or North-west Thracian Terrane; sensu Yanev et al., 2005) and the superimposed basement fragments, i.e., a north-western part of the Balkan Terrane in Bulgaria (Yanev et al., 2005), which is a continuation of the Getic/Supragetic Unit in Romania (sensu Iancu et al., 2005) and its analogue in Serbia (Fig. 2). ...
... Distinguishing Cadomian or Armorican crustal assemblages from Avalonian blocks means outlining the difference in the palaeocontinental positioning by employing analyses of the inherited eroded material transported into juvenile Neoproterozoic-Lower Palaeozoic basins, which were adjacent to present-day North Africa/South America or North Gondwana. Differentiating between Avalonian from Cadomian basements allows for a better insight into primordial plate-tectonic staging and palaeogeography, which is becoming increasingly popular in SEE (e.g., Ustaömer et al., 2005Ustaömer et al., , 2011Balica, 2013, 2016;Balintoni et al., 2010Balintoni et al., , 2011aBalintoni et al., , 2011bBalintoni et al., , 2014Himmerkus et al., 2006Himmerkus et al., , 2007Himmerkus et al., , 2009Kounov et al., 2012;Anti c et al., 2016). These ancient crustal fragments are represented by the Avalonian-Cadomian systems (750-520 Ma, Kounov et al., 2012, and references therein) comprising oceanic, intra-oceanic, cratonic, reworked-cratonic and continental magmatic arc remnants initially detached by the Iapetus opening. ...
... The cooling age of the SMM is estimated to be between the Cretaceous and Eocene ages (Anti c et al., 2015). Further in the Eastern Mediterranean, Ustaömer et al. (2005) attribute the older ages from the Bolu Massif (Istanbul Block) in Turkey to the existence of a very late Precambrian arc magmatism related to Balica, 2016). Inset from Samson (2005) shows a histogram, using 50 Ma increments for the combined data sets. ...
This review deals with a highly complex set of dismembered peri-Gondwanan exotic polymetamorphic basement systems accommodated outside of the well-explored European Variscides, extending from the controversial Serbo-Macedonian hinterland up to the East Moesian Alpine foreland. The isotopic and limited detrital zircon ages are coupled with the lithotectonic and palinspastic record in order to restore the earliest peri-Gondwanan developments in modern-day South-east Europe (Carpatho-Balkanides and surrounding areas). The results suggest that these rather bewildering, occasionally underexplored tectonometamorphic suites exhibit Cadomian arc inheritance in a flanking part of this belt, whilst inferior Avalonian are positioned more internally.
Here the full text link: https://authors.elsevier.com/a/1YrrZ3qItyaZW
... The possibility of a spatial continuity of an Ordovician-Devonian magmatic belt in the Balkan and Asia Minor was already raised in previous studies (i.e., Keay, 1998;Meinhold et al., 2010). In terms of their provenance, the Istanbul terrane is considered as being an Avaloniantype terrane (e.g., Ustaömer et al., 2005Ustaömer et al., , 2011, while the Sakarya and Serbo-Macedonian Massif are Cadomian-type (e.g., Meinhold et al., 2010;. This therefore suggests that at the time of the 450-400 Ma magmatic activity in the studied region, peri-Gondwanan terranes of both types were already connected. ...
... The Avalonian-type Istanbul-Zonguldak terrane was likely a part of the Avalonian or a related microplate, as it was deduced from its Ordovician trilobite fauna, its detrital zircon signal (Okay et al., 2006;Ustaömer et al., 2005Ustaömer et al., , 2011 and ...
... The isotopic properties of the Pirgadikia inlier are analogous to the Avalonian-type Istanbul-Zonguldak terrane: both basements comprise ca. 575 Ma-aged orthogneisses (Himmerkus et al. 2006;Okay et al, 2008 and references therein; Ustaömer et al., 2005) and cover strata of Istanbul (sensu stricto) and Zonguldak terranes, have similar detrital zircon age spectra (Ustaömer et al., 2011). The association between the Avalonian-type Pirgadikia inlier and the (Fig. 7D), were also affected by the Variscan magmatic activity. ...
Between the Eastern Mediterranean basin in the south and the East European (Baltica) Craton to the north, we distinguish two fundamental pre‐Variscan geological domains: an Internal domain which hosts Ordovician‐Devonian (450‐400 Ma) igneous rocks and detrital zircon populations, and an External domain which contains no 450‐400 Ma zircon ages. From the Balkan peninsula to the Turkish plate, the aforementioned Internal domain includes the Serbo‐Macedonian Massif, the Istanbul and Sakarya terranes, whereas the External domain, holding a more distal position relative to Baltica, includes the Pelagonian terrane and the External Hellenides. The two domains are interpreted as two consecutive (i.e., Caledonian and Variscan) Paleozoic accretionary belts, attached to the southern margin of Baltica.
The Cycladic and Pelagonian terranes are currently juxtaposed along‐strike of the central Hellenides in northern Greece. The Cycladic Massif is a Cadomian‐type terrane, while the Pelagonian displays an Avalonian‐type affinity. Despite its Avalonian affinity, the Pelagonian lacks Ordovician‐Devonian (450‐400 Ma) zircon ages. In contrast, detrital zircon grains of such ages are abundant in the Cycladic Massif. In this study, the Ordovician‐Devonian detrital zircon population is recognized also in pre‐Variscan (>310 Ma) Cycladic Basement from Ios and Naxos islands, affiliating the Cycladic Massif with the Internal (Caledonian) domain. This indicates that the Caledonian accretion incorporated some Cadomian‐type terranes. It also suggests that the protolith of the Cycladic blueschists was deposited within the Internal domain, i.e., northeast of the Pelagonian terrane. This recognition helps to reconstruct the Paleozoic and Mesozoic paleogeography of the peri‐Gondwanan terranes.
... In samples 27-2, the ages of the two magmatic cores are 599 Ma and 324 Ma ( Figure S2c). These ages correspond to Late Ediacaran to Ordovician and Carboniferous magmatism in the İstanbul-Zonguldak Tectonic Unit as found by Ustaömer et al. (2005) and Şen (2021, 2022a, 2023a). In sample 14, the ages of the magmatic cores, ranging from 271 to 263 Ma, correspond to the crystallization age of the olivine-bearing basalt ( Figure S2a). ...
... The locations of the dykes are given on the map. Isotopic ages are fromUstaömer et al. (2005) and Şen (2022a) for Late Ediacaran intrusions and dykes,Yiğitbaş et al. (1999) andBozkurt et al. (2013a) for Early Cambrian dykes and Çele meta-ophiolite,Şen (2023a, 2023c) for Ordovician dykes,Şen (2022b) for Silurian dykes,Şen (2021) andŞen and Karaağaç (2024) for Late Devonian-Late Carboniferous dykes,Aysal et al. (2018) for Late Permian granite, Şen (2012),Yılmaz-Şahin et al. (2012) andAysal et al. (2017) for Late Cretaceous intrusions,Şen (2020) for Middle Eocene sub-volcanic rocks. ...
Permo-Triassic intrusive rocks and back-arc basins are exposed in the İstanbul-Zonguldak Tectonic Unit in the West Pontides. Their tectono-magmatic history, thus to the evolution of the back-arc basins, is poorly understood. Here, I present on olivine-bearing basalt and andesite dykes and granite dykes and pyroxene-bearing andesite dykes of Permo-Triassic crystallization and their Pb-loss ages from the basement rocks and sedimentary rocks in the İstanbul-Zonguldak Tectonic Unit (NW Turkey). They have holocrystalline and porphyritic to vitrophyric textures. U-Pb dating of igneous zircon grains from olivine-bearing basalt and andesite dykes and granite dykes yielded Middle Permian ages of ca. 270.1 ± 1.1 to 261.4 ± 1.7 Ma (2σ), and pyroxene-bearing andesite dykes obtained Early Triassic ages of ca. 252.1 ± 2.4 to 250.1 ± 2.0 Ma (2σ). Their young ages of the dykes yielded Late Triassic ages of ca. 228 to 220 Ma (2σ). Geochemically, the Middle Permian dykes have a calc-alkaline affinity and are notable for subduction components, as indicated by the presence of distinct negative Nb anomalies. Early Triassic dykes show alkaline signatures and show within-plate character, corresponding to prominent positive Nb anomalies. Combined with data from the literature, the Middle Permian dykes are magmatic products associated with the Tethys Ocean subducting under the Pontides and the Early Triassic dykes are magmatic pulses related to the rifting of the Permo-Triassic back-arc basins. The Late Triassic young ages of the Permo-Triassic dykes in the İstanbul-Zonguldak Tectonic Unit represent a deformation event corresponding to the Cimmerian orogeny, and this implies that the Permo-Triassic back-arc basins closed during the late Triassic.
... The IZT includes various outcrops of Neoproterozoic metagranitoids (e.g., Karadere Unit and Bolu Massif, ca. 590-560 Ma, Chen et al., 2002;Ustaömer et al., 2005;Okay et al., 2008), and these areas could be potential source areas of the Neoproterozoic zircons (<~600 Ma) reported from the metasedimentary rocks from both the Geme Complex and the Serveçay Unit (Fig. 1a). The other dominant population in the samples from the Geme Complex and the Serveçay Unit is represented by Devonian zircons, and the potential source region of these zircons may be Devonian granitoids (e.g., Karacabey, Çamlık and Bayatlar granitoids, ca. ...
... The Serveçay Unit is mainly characterized by Neoproterozoic and Devonian zircons (53 %) and has a Permian maximum depositional and age of metamorphism (Fig. 9, Table 3). Therefore, it may have been deposited in an area close to the margins of IZT and western SCT since this continental fragment includes potential Neoproterozoic and Devonian magmatic source areas (e.g., Okay et al., 1996;Chen et al., 2002;Ustaömer et al., 2005;Sunal, 2012). Subsequently, the Serveçay Unit could have been metamorphosed during the Permian period in relation to the Variscan events that is obviously traced throughout the SCT (Fig. 1a, e.g., Okay and Topuz, 2017). ...
The pre-Jurassic tectonic evolution of the Central Pontides in northern Turkey is still poorly understood due to the lack of detailed geochemical and geochronological data from the basement units. Therefore, this study reports for the first time combined whole rock geochemistry, trace element data and U-Pb ages for detrital zircons, and Ar-Ar geochronological data from the metasedimentary rocks of the Devrekani Massif, Geme Complex, and the Serveçay Unit to better understand their provenance, depositional age characteristics, and tectonic evolutions. The detrital zircon U-Pb data of metasedimentary units from the Devrekani Massif, Geme Complex, and the Serveçay Unit yield ca. 191, 185 and 298 Ma maximum depositional ages (youngest age peaks), respectively. The Devrekani Massif is dominated by Permo-Carboniferous-aged detrital zircons (67 %), whereas Neoproterozoic and Devonian-aged detrital zircons are more common in the Geme Complex (47 %) and the Serveçay Unit (53 %). These distinct age distributions clearly indicate that the Devrekani Massif may has been deposited in a dissimilar location compared to the Geme Complex and the Serveçay Unit. Furthermore, in contrast to the Devrekani Massif, the source area of the metasedimentary rocks from the Geme Complex is comparable with that of the Serveçay Unit. Lastly, the obtained detrital zircon U-Pb and mica Ar-Ar ages suggest that the Devrekani Massif and the Geme Complex were deposited and metamorphosed during the Early and Middle Jurassic, respectively. The Serveçay Unit was deposited and metamorphosed in the Permian.
This paper is dedicated to the memory of Prof. Dr. Aral Okay, who passed away recently. We would not be able to figure out the geological problems of the Central Pontides without his valuable contributions.
... The late Neoproterozoic zircons show igneous zoning and are interpreted as reflecting the ages of the igneous protolith. Similar ages were reported from the basement of the İstanbul Zone in the Bolu Massif, in the Karadere area and in the Armutlu Peninsula (Chen et al., 2002;Ustaömer et al., 2005;Okay et al., 2008;Akbayram et al., 2013). Especially important are the large late Neoproterozoic (565-576 Ma) granites intruding into the low-grade metavolcanic rocks in the Bolu Massif ( Figures 1 and 13a) (Ustaömer et al., 2005;Bozkurt et al., 2013b). ...
... Similar ages were reported from the basement of the İstanbul Zone in the Bolu Massif, in the Karadere area and in the Armutlu Peninsula (Chen et al., 2002;Ustaömer et al., 2005;Okay et al., 2008;Akbayram et al., 2013). Especially important are the large late Neoproterozoic (565-576 Ma) granites intruding into the low-grade metavolcanic rocks in the Bolu Massif ( Figures 1 and 13a) (Ustaömer et al., 2005;Bozkurt et al., 2013b). ...
... They represent an Avalonian arc (Ustaömer and Rogers, 1999) intruded by the Avalonian intrusive granitic rocks (c. 576 Ma; Ustaömer et al., 2005) and completely cut by riftrelated Late Ediacaran intrusive magmatic bodies (c. 565-556 Ma; Şen, 2021a) ( Figure 3). ...
... The Yellice metavolcanics standing for the Avalonian arc are emplaced by Late Ediacaran rift-related intrusive rocks (c. 565-556 Ma; Ustaömer et al., 2005;Şen, 2021a). This also corresponds to the beginning of the sedimentation time of the rift fills (Kurtköy Formation) that were are cut by Late Ediacaran rift-related small intrusions (c. ...
The İstanbul-Zonguldak Tectonic Unit is regarded as the easternmost fragment of Avalonia-Carolina and designated as Far East Avalonia. Its stratigraphy is characterized by discontinuous sedimentation from Late Ediacaran to Late Carboniferous. In the western part of the block, known as İstanbul Terrane, the Gözdağ Formation is represented by lagoonal sedimentary rocks consisting of shale-sandstone with limestone of Middle Ordovician-Lower Silurian age. Here, I report on stratigraphic positions and petrographical and geochemical data of fine-and coarse-grained tuffs and lavas in the Late Ordovician strata of the Gözdağ Formation. The fine-and coarse-grained tuffs have pyroclastic and the lavas have porphyritic, vitrophyric and aphanitic textures. The fine-and coarse-grained tuffs are of Sandbian and Katian ages, and the lavas have Hirnantian ages, according to the stratigraphic positions of the Late Ordovician volcanic rocks. The fine-grained tuffs have high potassium calc-alkaline, and the coarse-grained tuffs and lavas have a calc-alkaline character. They are devoid of noticeable within plate components, as deduced by the presence of obvious negative Nb anomalies, and they have subduction signatures. In conjunction with data from the literature, the Sandbian fine-grained tuffs were deposited in a lagoonal depocenter in the İstanbul-Zonguldak Tectonic Unit in the earliest Late Ordovician due to multiple Plinian-type eruptions during the last phase of the Taconic orogeny, which formed between the Piedmont Terrane and Laurentia. The Katian coarse-grained tuffs were products of volcanic activities formed in the arc settings during the last stage of depletion of the Teisseyre-Tornquist Ocean, lying between Avalonia and Baltica. The Hirnantian lavas were formed by flowing in a lagoonal depocenter of the İstanbul-Zonguldak Tectonic Unit during the soft-docking of Avalonia and Baltica, known as the pre-Caledonian orogeny.
... As discussed above, geochronological and petrological data in this study show that the protoliths of the garnet amphibolitic slices in the Yahyaalcı-Alaşehir (Bozdağ Nappe) and Camlica-Tire Klippe (Çine Nappe) areas and retrogressed eclogitic slices in the Yenişehir-Kiraz area (Çine Nappe) may have been sourced from the Cadomian rift-related meta-mafic dykes and meta-diabase dykes of the Gögebakan Formation or their higher metamorphosed equivalents in the northern and deeper subducted parts of the Tauride-Anatolide Platform. Detailed tectonic scenarios have been proposed that suggest the basement of the Tauride-Anatolide Platform represents acidic/transitional magmatic products and fore-arc sedimentary deposits along the Avalonian-Cadomian magmatic arc (e.g., Chen et al., 2002;Yiğitbaş et al., 2004;Ustaömer et al., 2005;Gürsu et al., 2015;Gürsu, 2016), which were formed by southward intra-oceanic subduction of the Proto-Tethys ocean between 570 Ma and 590 Ma. The arc-extension on the peri-Gondwanan continental lithosphere due to the slab-roll back within this ocean resulted in thinning of the continental lithosphere and intrusion of felsic/transitional magmas and their mafic equivalents (Sandıklı-Afyon, İhsaniye-Afyon, Çine Nappe of Menderes Massif) between 560 Ma and 545 Ma (Gürsu et al., 2004: Gürsu and Göncüoğlu, 2005Gürsu 2008Gürsu , 2016. ...
... This magmatic activity was attributed to the late phase of the Cadomian Orogeny within the Pan-African mega-cycle in NW Gondwana observed in the Istanbul Zonguldak Terrane (Ustaömer, 1999;Chen et al., 2002;Yiğitbaş et al., 2004;Ustaömer et al., 2005), in the Istranca Terrane (Şahin et al., 2014;Yılmaz et al., 2021), in the Tauride-Anatolide Platform (Gürsu and Göncüoğlu, 2005Gürsu, 2008Gürsu, , 2016, in the South Anatolian Autochthone Belt (Ustaömer et al., 2009(Ustaömer et al., , 2012Gürsu et al., 2015), and in several peri-Gondwanan terranes in N Africa, W and E Europe, Iran, Tibet, and SE Asia (details in Jarrar et al., 1992;Neubauer, 2002;Murphy et al., 2002Murphy et al., , 2004Ramezani and Tucker, 2003;Keppie et al., 2003;Gürsu et al., 2004Gürsu et al., , 2015Linnemann et al., 2004Linnemann et al., , 2007Gürsu, 2008Gürsu, , 2016Pouclet et al., 2007;Nadimi, 2007;Meert and Lieberman, 2008;Hassanzadeh et al., 2008;Fritz et al., 2013;Hefferan et al., 2014). ...
The age, emplacement, and metamorphic history of the garnet amphibolitic and retrogressed eclogitic slices in the Menderes Massif (Eastern Aegean) have been a matter of debate since the 1990’s. Late Cretaceous garnet amphibolitic and retrogressed eclogitic slices in the Bozdağ and Çine nappes show low-angle tectonic contacts with the surrounding Early Cambrian meta-siliciclastics in the Alaşehir-Yahyaalcı and late Neoproterozoic basement rocks in the Birgi and Tire-Çamlıca Klippe in the northern Menderes Massif. Lower and upper intercept ages on the discordia diagrams of the garnet amphibolitic slices are 82 ± 230 Ma and 554 ± 14 Ma, respectively, in the Yahyaalcı-Alaşehir area of the Bozdağ Nappe; and 96 ± 260 Ma and 550 ± 13 Ma, respectively, in the Camlica-Tire Klippe area of the Çine Nappe. Retrogressed eclogitic slices give dates of 81 ± 13 Ma lower intercept and 546 ± 13 Ma upper intercept discordant ages in the Yenişehir-Kiraz area of the Çine Nappe. Lower intercept age of 81 ± 13 Ma is supported by two spots dated on metamorphic zircons showing positive Eu patterns yielding 86.0 ± 1.3 Ma concordant age. Zircon U-Pb dating on the oscillatory zoning spots are dated as 537.5 ± 1.6 Ma (mean square weighted deviation [MSWD] = 1.5, n = 41) for the garnet amphibolic slices in the Yahyaalcı-Alaşehir area (Bozdağ Nappe), 539.0 ± 1.1 Ma (MSWD = 1.4, n = 56) for the garnet amphibolite slices in the Camlica-Tire Klippe area (Çine Nappe), and 536.6 ± 2.3 Ma (MSWD = 1.7, n = 32) for the retrogressed eclogitic slices (Çine Nappe). These ages combined with Eu negative anomalies on the dated spots are evaluated as representing their magmatic crystallization ages of the protoliths. Garnet isopleth intersections and pseudosections gave pressure-temperature conditions of 14 kbar and ∼680 °C for the retrogressed eclogites, whereas garnet amphibolites display disequilibrium in whole rock scale. We propose that the age of their protoliths likely correlate with the Cadomian rift-related Early Cambrian meta-mafic dykes that were subducted beneath the İzmir-Ankara-Erzincan Neotethyan lithosphere during the Late Cretaceous. The new rutile U-Pb age of 30.1 ± 2.0 Ma supports that the tectonic slices of the İzmir-Ankara oceanic lithosphere and metamorphosed Tauride-Anatolide continental margin were emplaced onto the Menderes Massif to generate the “main Menderes metamorphic terrane” during the latest Paleocene and early Eocene.
... The İZ is located mostly to the north of the IPSZ (Şengör and Yılmaz 1981;Okay and Tüysüz 1999;Akbayram et al. 2017) (Figure 1, 2). It has a high-grade Precambrian metamorphic basement (Akbayram et al. 2013;Chen et al. 2002;Ustaömer et al. 2005). This basement is nonconformably overlain by an almost continuous succession of Palaeozoic rocks extending from Lower Ordovician to Upper Carboniferous, which were later intruded by Late Permian granitoids ( Figure 3) (Bürküt 1966;Yılmaz 1977;Görür et al. 1997;Özgül et al. 2005, 2009Şengör and Özgül 2010;Yılmaz-Şahin et al. 2010;Özgül 2011Şengör 2011;Lom et al. 2016). ...
... In contrast, no granitoid of the Precambrian age is reported from the Sakarya Zone. Thus, we agree that the amphibolites cut by the dated meta-granitoids belong to basement rocks of the İstanbul Zone and represent widespread Cadomian arc magmatics in Anatolia (Ustaömer 1999;Gürsu and Göncüoğlu 2005;Ustaömer et al. 2005;Gürsu and Göncüoğlu 2006;Gürsu et al. 2015;Özbey et al. 2021). ...
The Almacık Block is a tectonic sliver formed during the activity of the North Anatolian Fault Zone (NAFZ). It includes two important tectonic zones of the Western Pontides (NW Anatolia): the İstanbul and the Sakarya Zones meet along a suture zone called the Intra-Pontide Suture Zone (IPSZ). The units within the İstanbul Zone are exposed in the eastern part of the Almacık Block, whereas the rocks of the Sakarya Zone are exposed in the west. In the presented study, some of the magmatic rocks have been analysed using the zircon U-Pb method: these rocks have previously been either incorrectly or not dated. The U-Pb results have shown that some of the granitic rocks in
the İstanbul Zone, which intruded into the amphibolites of the Intra-Pontide Suture Zone, have a crystallization age of 559–556 Ma. A granitoid block in the Upper Cretaceous wild flysch formed over the units of the İstanbul Zone had an age of ~566 Ma. Two distinct granitoid bodies in the Sakarya Zone were dated at 404.5 ± 3.9 Ma (Early Devonian) and 161.8 ± 0.82 Ma (Late Jurassic) ages. The palaeo-exhumation evolutions of the zones were obtained using the zircon (U-Th)/He technique (ZrHe) to understand the differences in the geological evolution of the individual zones. ZrHe ages of the samples obtained from the İstanbul Zone indicate a pronounced Early Cretaceous palaeo-exhumation period. The Middle-Upper Jurassic Mudurnu Formation in the Sakarya Zone gave ZrHe ages close to its sedimentation age, which indicates that the major part of the unit was
not buried too deep to open the ZrHe closure system. Unlike those the İstanbul Zone, the main ZrHe age peaks of the Sakarya Zone are ~202, 160, 98, 74, and 52 Ma. Finally, a sample of the metamorphic rocks that were assigned to the IPSZ yielded a peak age of ~63 Ma, which indicates that the final closure of the Intra-Pontide Ocean (IPO) took place during the Early Tertiary.
... The İZ is located mostly to the north of the IPSZ (Şengör and Yılmaz 1981;Okay and Tüysüz 1999;Akbayram et al. 2017) (Figure 1, 2). It has a high-grade Precambrian metamorphic basement (Akbayram et al. 2013;Chen et al. 2002;Ustaömer et al. 2005). This basement is nonconformably overlain by an almost continuous succession of Palaeozoic rocks extending from Lower Ordovician to Upper Carboniferous, which were later intruded by Late Permian granitoids ( Figure 3) (Bürküt 1966;Yılmaz 1977;Görür et al. 1997;Özgül et al. 2005, 2009Şengör and Özgül 2010;Yılmaz-Şahin et al. 2010;Özgül 2011Şengör 2011;Lom et al. 2016). ...
... In contrast, no granitoid of the Precambrian age is reported from the Sakarya Zone. Thus, we agree that the amphibolites cut by the dated meta-granitoids belong to basement rocks of the İstanbul Zone and represent widespread Cadomian arc magmatics in Anatolia (Ustaömer 1999;Gürsu and Göncüoğlu 2005;Ustaömer et al. 2005;Gürsu and Göncüoğlu 2006;Gürsu et al. 2015;Özbey et al. 2021). ...
The Almacık Block is a tectonic sliver formed during the activity of the North Anatolian Fault Zone (NAFZ). It includes two important tectonic zones of the Western Pontides (NW Anatolia): the İstanbul and the Sakarya Zones meet along a suture zone called the Intra-Pontide Suture Zone (IPSZ). The units within the İstanbul Zone are exposed in the eastern part of the Almacık Block, whereas the rocks of the Sakarya Zone are exposed in the west. In the presented study, some of the magmatic rocks have been analysed using the zircon U-Pb method: these rocks have previously been either incorrectly or not dated. The U-Pb results have shown that some of the granitic rocks in the İstanbul Zone, which intruded into the amphibolites of the Intra-Pontide Suture Zone, have a crystallization age of 559-556 Ma. A granitoid block in the Upper Cretaceous wild flysch formed over the units of the İstanbul Zone had an age of ~566 Ma. Two distinct granitoid bodies in the Sakarya Zone were dated at 404.5 ± 3.9 Ma (Early Devonian) and 161.8 ± 0.82 Ma (Late Jurassic) ages. The palaeo-exhumation evolutions of the zones were obtained using the zircon (U-Th)/He technique (ZrHe) to understand the differences in the geological evolution of the individual zones. ZrHe ages of the samples obtained from the İstanbul Zone indicate a pronounced Early Cretaceous palaeo-exhumation period. The Middle-Upper Jurassic Mudurnu Formation in the Sakarya Zone gave ZrHe ages close to its sedimentation age, which indicates that the major part of the unit was not buried too deep to open the ZrHe closure system. Unlike those the İstanbul Zone, the main ZrHe age peaks of the Sakarya Zone are ~202, 160, 98, 74, and 52 Ma. Finally, a sample of the metamorphic rocks that were assigned to the IPSZ yielded a peak age of ~63 Ma, which indicates that the final closure of the Intra-Pontide Ocean (IPO) took place during the Early Tertiary. ARTICLE HISTORY
... The subduction produced continental rifting at the northern Gondwanan margin due to slab roll-back and intense igneous activity at 550-530 Ma due to the crustal thinning throughout Avalonian-Cadomian-type peri-Gondwanan terranes (e.g. Fernández-Suárez et al., 2000Murphy et al., 2002Murphy et al., , 2004von Raumer et al., 2003;Neubauer, 2002;Ustaömer et al., 2005Ustaömer et al., ,2009Ustaömer et al., , 2012Gürsu and Göncüoğlu, 2005, 2006, 2008Gürsu, 2008;Hefferan et al., 2014;Gürsu et al., 2015;Dörr et al., 2015). Massive quartz rich-siliciclastic sequences were deposited in a shallow marine to fluvial environments in the peri-Gondwanan terranes from Iberia (Spain), Avalonia (France), Saxo-Thuringia (Germany), Corsica (Italy), Carpathians (Romania), S Turkey, Iraq and Iran along the Avalonian-Cadomian Magmatic Arc. ...
... Arc formation was followed by diachronous arc-trench collisions generating arc-related granitic rocks and their volcanic equivalents between 590-570 Ma and then I-type extensional magmatism and its volcanic equivalents between 570-545 Ma (Fig. 16 C) (Ustaömer, 1999;Ustaömer et al., 2005Ustaömer et al., , 2009Ustaömer et al., , 2012Gürsu et al., 2004Gürsu et al., , 2014Gürsu and Göncüoğlu, 2006;Gürsu, 2016). Roll-back of the Prototethys oceanic lithosphere resulted in extension and genesis of the initial and mature stages of continental rifting by back-arc extension, during which ...
Detrital U-Pb age peaks and εHf(t) and TDM(Hf) of peri-Gondwanan units of S Turkey indicate that they may have been derived from Neoproterozoic igneous suites in the Sinai Peninsula (Egypt), Israel (Elat) and Eastern Desert (Egypt) part of the Nubian Shield. Early Cambrian siliciclastics in the peri-Gondwanan units of S Turkey consist of quartzites in the Menderes Massif of the Tauride-Anatolide Platform (TAP), meta-quartz arenites in the different Alpine tectonic slivers of the TAP-margin and quartz-arenites in the Southeast Anatolian Autochthon Belt (SAAB). Geochemical data indicate that these sediments are likely to be derived from sedimentary recycling processes in oxic depositional basins within a continental back-arc tectonic setting. They were opened after the formation of the Avalonian-Cadomian magmatic arc. In the TAP, the youngest detrital zircon 238U/206Pb ages are range from 530.6 +6.3/-12.0 Ma to 549.4 ±10 Ma and from 551.9 +7.9/-8.4 Ma to 545.8 ±11 Ma in the SAAB verifying the Early Cambrian maximum depositional ages for the sampled siliciclastic successions. In the TAP, meta-quartz arenites, Neoproterozoic detrital zircons make up about 75% of the total grains, whereas they constitute about 88 % in the SAAB sedimentary rocks. Tonian zircons in the TAP (> 40 %) and SAAB (< 32 %) reveal key populations to determine their provenance and the paleotectonic positions of the respective terranes. The combination of U-Pb age and Lu-Hf systematics in the detrital zircons of the TAP and SAAB show that age groups at 535 to 562 Ma and 888 to 3370 Ma are mainly represented by the zircons derived from evolved sources with a limited juvenile component. The predominant zircon age groups between 577 to 854 Ma in the TAP and SAAB, on the other hand, were derived from juvenile to evolved sources. Non-parametric Kolmogorov-Smirnov tests suggest that Early Cambrian successions in the TAP (except Kocaosman-Isparta) may have been located in similar paleogeographic locations with coeval successions in the SAAB during the Early Cambrian. U-Pb geochronology and Lu-Hf systematics of the Early Cambrian successions in the TAP and SAAB indicate that the dominant detrital zircon age groups were mainly sourced and transported to continental back-arc fluvial to shallow marine sedimentary environments from igneous rocks of the Nubian Shield and the Saharan Metacraton by a combination of the glaciers, eolian events and multiple-stage erosional and sedimentary recycling processes during the Early Cambrian (ca 520 Ma). The provenance of the Early Cambrian successions in the TAP and SAAB correlate with the provenance areas of the coeval siliciclastic sequences in Israel and Jordan (Arabian Shield), Iraq and Iran and the peri-Gondwanan Carpathians, rather than the Early Cambrian successions in the central and southern European peri-Gondwanan terranes.
... Neoproterozoic and Ordovician ages are related to the Cadomian orogeny and the opening of Rheic Ocean, respectively (Okay et al. 2008;Akbayram et al. 2013;Özbey et al. 2021). Cadomian basement rocks were reported from the Strandja Massif (Yılmaz-Şahin et al. 2014), the Istanbul Zone (Chen et al. 2002;Ustaömer et al. 2005), the Armutlu-Ovacık Zone (Okay et al. 2008;Akbayram et al. 2013;Özbey et al. 2021), the Biga Peninsula (Tunç et al. 2014). High-grade metamorphic rocks of amphibolite, gneiss and metagranite crop out in the north of Pamukova, Gemlik and Geyve villages, which are focused in this study (Fig. 2). ...
... The metamorphic basement of the Istanbul Zone is mainly made up of high-grade metamorphic rocks of gneiss, amphibolite and metaophiolite intruded by large granitoids (Ustaömer and Rogers 1999;Yiğitbaş et al. 2004). The zircon ages of these granitoids were determined as 560-590 Ma by U-Pb and Pb/Pb methods (Chen et al. 2002;Ustaömer et al. 2005). Türkecan and Yurtseven 2002;Aksay et al. 2002;Okay et al. 2008) The basement of the Istanbul Zone shows similarities in age and geochemistry to the Pan-African basement of the northern Gondwana margin (Okay et al. 2008). ...
The Pamukova metamorphics mainly consist of amphibolite, gneiss and metaquartzite exposed on the Armutlu Peninsula in northwest Turkey. Whole-rock major and trace element chemistry were used to reveal protolith, source characteristics and tectonic setting of amphibolites in this study. The amphibolites are dark-green colored, medium to coarse-grained, banded and have NNE-SSW-directed strikes in the field. The protolith of amphibolites is basalt to basaltic andesite based on trace element chemistry. Ti/Y (112–612) and Nb/Y (0.01–0.6) ratios suggest that amphibolites were derived from a tholeiitic magma. The immobile trace element tectonic-environment discrimination diagrams demonstrate that amphibolites from the Pamukova metamorphics have island arc affinities and boninitic character. Amphibolite samples display flat rare earth element (REE) patterns and enrichment of large ion lithophile elements (LILEs; i.e., Rb, Ba, Th) and depletion in high field strength elements (HFSEs; i.e., Nb, Th, Hf). The amphibolites show N-MORB characteristics on a multi-element diagram, which suggests that the protolith of amphibolites took place in a subduction-related setting. The low Ce/Pb (0.75–6.28) and high Ba/Nb (19.27–444) ratios in amphibolite samples reflect the influx of slab fluids/melts into the mantle wedge. Th/Yb and Ta/Yb ratios show that amphibolites were generated by the metamorphism of island arc-type basaltic protolith during the intra-oceanic subduction.
... Ten zircon grains in sample 46-1 (dacite dyke) define a concordia age of 556.2 ± 2.2 Ma (2σ, MSWD = 0.2), twelve zircon grains in sample 101 define a concordia age of 552.1 ± 2.8 Ma (2σ, MSWD = 1.2) and eight zircon grains in sample 4D also obtain a concordia age of 549.2 ± 2.3 Ma (2σ, MSWD = 0.1) (Figure 7b). In sample 46-1 and 4D, ages of the magmatic cores in the range of 579 to 565 Ma correspond to Late Ediacaran magmatism in the İZTU as found by Ustaömer et al. (2005). The ages of white spots on the zircons were calculated from concordant and discordant zircons. ...
... 591-569 Ma;Okay et al. 2008;Akbayram et al. 2013), (b) Late Ediacaran magmatism in Sünnice mountain (c. 575 Ma; Ustaömer et al. 2005) and (c) Middle-Late Ediacaran magmatism in Karadere (c. 590-568 Ma;Chen et al. 2002) (Table 1). ...
The İstanbul-Zonguldak Tectonic Unit is a part of Avalonia-Carolina and represents Far East Avalonia. It includes Ordovician to Carboniferous deposits which unconformably overlie Late Neoproterozoic metamorphic rocks. Timing of its detachment from West Gondwana-land, thus rifting of the Rheic Ocean, is poorly known. Here, I report on dacite, diabase and andesite dykes of Late Ediacaran igneous crystallization ages from the basement rocks and rift-deposits in the İstanbul-Zonguldak Tectonic Unit (NW Turkey). They are folded about a consistent axis and have porphyritic to intersertal textures. U-Pb dating on igneous zircons from folded dykes yielded Late Ediacaran ages of ca. 556.2 ± 2.2 Ma (2σ) and 552.1 ± 2.8 to 549.2 ± 2.3 Ma (2σ). Late Ediacaran dykes show calc-alkaline and alkaline affinities, and contain with-in plate components. Rift-related Late Ediacaran magmatism shows that the Yellice arc changed from an arc to a back-arc basin and the rift-deposits formed during the late Ediacaran due to the arc rifting. In conjunction with the data from literature, I suggest that the rift-related magmatism is related to the rifting event during the late Ediacaran, leading to the detachment of this continental block from the West Gondwana-land, thus to the opening of the Rheic Ocean, and Early Cambrian deformation event correspond to the adding of the Kraishte terrane with Far East Avalonia. The docking of the Kraishte terrane led to the deformation of Late Ediacaran dykes. Overall, these data indicate that the depositional time of sedimentary rocks in the continental fragment should have started during the late Ediacaran instead of Ordovician.
... The Sakarya Zone basement comprises Variscan plutonic and metamorphic rocks (Okay and Tüysüz, 1999), overlain by a Jurassic and younger sedimentary sequence (Okay and S ßahintürk, 1997;Eyuboglu, 2015). The Istanbul Zone, which is sandwiched between the Black Sea to the north and the Sakarya Zone to the south, is characterized by late Neoproterozoic metagranitoids (Chen et al., 2002;Ustaömer et al., 2005). The basement is unconformably covered by an Ordovician-Eocene sedimentary sequence (e.g. ...
... Thus, the zircon grains with ages of~650-540 Ma should be recycled from the Gondwana-related Pontides basement. This inference is also supported by the presence of 576-565 Ma granitic basement exposed in the Bolu Massif in the Western Pontides (Ustaömer et al., 2005). ...
Resolving the time of rifting of the Black Sea basin is critical to reconstructing the tectonic evolution of the Pontides arc in northern Turkey. U–Pb geochronology of detrital zircons from Middle Jurassic, Upper Cretaceous, and lower Eocene formations in the Eastern Pontides (NE Turkey), as well as published data from circum-Black Sea terranes, reveals that sediments preserved along with the northern (East European Craton-Scythian Platform) and southern (Eastern and Central Pontides-southern flank of the Greater Caucasus-Transcaucasus) margins of the Eastern Black Sea basin display distinct detrital provenances. The U–Pb detrital zircon ages of the sedimentary samples from the Eastern Pontides have distinct populations with ages of ∼650–540, ∼200, ∼170, ∼80, and ∼50 Ma. In contrast, the ages of the sedimentary samples from the northern Black Sea terranes are characterized by age peaks of ∼1400 and ∼1100 Ma compared to those of the Eastern Pontides. Only a few detrital zircons in the range of ∼650–540 Ma and <200 Ma are identified in the sedimentary samples from the northern Black Sea terranes. This contrast in detrital zircon ages, together with modal analysis of the samples and published paleocurrent data, suggests that Middle Jurassic–lower Eocene sedimentary samples in the Eastern Pontides were locally sourced from Gondwana affinity crustal basement rocks and associated Mesozoic–Cenozoic igneous rocks. Furthermore, there was no exchange of detritus across the Eastern Black Sea basin during the Middle Jurassic–early Eocene. These inferences require the Eastern Black Sea basin to have rifted in a back-arc setting behind the Eastern Pontides arc by the Middle Jurassic or survived as a relict basin of the Paleotethys.
... They are intruded by the Avalonian arcrelated granitic intrusions of Middle-Late Ediacaran age (c. 591-568 Ma; Chen et al. 2002;Ustaömer et al. 2005;Okay et al. 2008;Akbayram et al. 2013). In Sünnice mountain, the basement unit is composed of a high-grade metamorphic sequence dominated by migmatitic quartzo-feldspathic micaceous psammite and semipelite, representing an ancient continental basement (Demirci paragneisses; Yiğitbaş et al. 2008). ...
... Black box shows study area 2017; personal commun). They represent the Avalonian arc (Ustaömer et al. 2005). Early Cambrian and Early Ordovician small magmatic bodies (c. ...
The İstanbul–Zonguldak Tectonic Unit, which is devoid of Devonian–Carboniferous magmatism, is a continental fragment of Far East Avalonia. It was deformed by thrusting due to the collision with the Sakarya terrane with Minoa origin during the Carboniferous, and forms the Variscan foreland. The tectono-magmatic evolution of Devonian–Carboniferous, thus consumption evolution of the Rheic Ocean in Far East Avalonia, is poorly known. Diabase and basaltic andesite dykes show Late Devonian to Late Carboniferous igneous crystallization ages in the İstanbul–Zonguldak Tectonic Unit (NW Turkey). They have aphanitic to vitrophyric textures. U–Pb dating on igneous zircons from diabase and basaltic andesite dykes yielded Late Devonian age of ca. 381.3 ± 1.8 Ma (2σ) and Late Carboniferous ages of ca. 306.1 ± 3.3 to 301.5 ± 1.1 Ma (2σ), respectively. Geochemically, Late Devonian magmatism shows tholeiitic affinities and contains subduction and with-in plate components, but Late Carboniferous magmatism displays calc–alkaline signatures and includes subduction components. The Late Devonian dykes intruded into the continental block during the rifting of the Pripyat–Dnieper–Donets Basin in Baltica as a result of the north-subducting Rheic Ocean. While it proceeded to subduct under Far East Avalonia along the magmatic arc that was similar to the Hanseatic arc in East Avalonia, Late Carboniferous dykes emplaced into it in an arc-related setting. Also, Late Carboniferous magmatism that is related to magmatic arc displays that the collision of the İstanbul–Zonguldak Tectonic Unit and Sakarya terrane, described as the Variscan orogeny in the Pontides did not form during the Carboniferous.
... In the IZ terrane the Paleozoic sequence is continuous from Ordovician to Carboniferous with no intervening phases of magmatism or deformation (e.g., Görür et al., 1997;Ozgül, 2012). The Ordovician sedimentary rocks are underlain by Late Neoproterozoic granitoids (Ustaömer et al., 2005). The Late Neoproterozoic granitoids as well as the Paleozoic sedimentary sequence were deformed and metamorphosed during the Carboniferous and were subsequently intruded by syn-and post-tectonic Late Carboniferous and Permian granitoids (Yılmaz et al., 2012;Aysal et al., 2017Aysal et al., , 2018. ...
... The Late Neoproterozoic granitoids as well as the Paleozoic sedimentary sequence were deformed and metamorphosed during the Carboniferous and were subsequently intruded by syn-and post-tectonic Late Carboniferous and Permian granitoids (Yılmaz et al., 2012;Aysal et al., 2017Aysal et al., , 2018. These intrusive rocks show a wide range of ages from 309 to 235 Ma similar to the plutonic rocks described in the Strandja massif, Istanbul area and central Pontides (Ustaömer et al., 2005;Sunal et al., 2006;Şahin et al., 2014;Machev et al., 2015;Aysal et al., 2018). ...
In the Boyalı area (northern Anatolia), a thick succession of the Early Maastrichtian - Middle Paleocene Taraklı Flysch crops out. The Taraklı Flysch represents a foredeep sediment deposited during the final stage of collision between the Sakarya and Istanbul-Zonguldak continental margins, that developed as a consequence of the closure of the Intrapontide oceanic basin. The top of the Taraklı Flysch is characterized by a level of slide-block in shaly-matrix lithofacies that can be considered as the result of several fast catastrophic events predating the closure of the basin and its deformation. This level consists of slide-blocks surrounded by monomict pebbly-mudstones and pebbly-sandstones. Among the slide-blocks, the biggest one consists of quartz-monzonites and leucocratic granodiorites of Late Permian age (260.8 ± 2.2 Ma) dated by zircon LA-ICP-MS method. By comparison with the regional data, the source area of these granitoids can be identified in the Istanbul-Zonguldak terrane. This evidence suggests a new picture for the paleogeographic setting of the ultimate stage of the continental collision between the Istanbul-Zonguldak and the Sakarya continental margins. In this scenario the coarse-grained deposits of the Taraklı Flysch are supplied by an orogenic wedge, consisting of oceanic units topped by the Istanbul-Zonguldak terrane. This orogenic wedge represented the north side of the foredeep, while the southern one was represented by the still undeformed Sakarya continental margin.
... The Intra-Pontide Suture Zone separated the Istanbul and Sakarya Zones (Şengör and Yılmaz 1981). It includes a late Precambrian crystalline basement consisting of amphibolite, gneiss, metaophiolite, metavolcanic rocks and Late Precambrian granitoids (Chen et al. 2002;Yığıtbaş et al. 2004;Ustaömer et al. 2005). Stratigraphic features of the western and eastern sections of the Istanbul Zone also present significant differences (Okay 2008). ...
It is known that the site classifications are closely related to the damages caused by earthquakes in areas with increased seismic hazard. Additionally, another important parameter utilized to identify the damage is the Peak Ground Acceleration (PGA) value. While measurements and the GMPE are utilized to identify PGA values, site classification is usually conducted by using the Vs30 value. This study aims to identify the site classifications for Bursa province by using a different approach, namely, the H/V spectral ratio method based on the dominant periods. In this regard, 205 records belonging to 82 earthquakes recorded by 41 strong ground motion stations located in Bursa province were utilized. A mean H/V spectral ratio curve was developed for each station based on the Fourier and response spectra of these earthquake records. Generally, double or multiple peaks resulting from the site structure were observed in the H/V curves. Furthermore, for the station locations, the evaluations were conducted in accordance with the site classifications per the dominant period as it is suggested in the literature. The stations were identified as all of the site classifications suggested by (Zhao et al. Bull Seismol Soc Am 96:914–925, 2006), as SC-1, 2, 3 and 5 suggested by (Fukushima et al. J Earthquake Eng 11:712–724, 2007) and as CL I, II, III, IV and VII suggested by (Di Alessandro et al. Bull Seismol Soc Am 102:680–695, 2012). Additionally, various Spectral Acceleration estimations were made with different GMPE equations for scenario earthquakes, and the results were compared with the design spectra suggested by the Turkish Building Earthquake Code (TBEC 2018). As a result of the study, the H/V spectral curves were generated according to both Fourier and response spectra; using a great number of earthquake data, the hazard was assessed by the soil dominant period-based for the first time in Bursa province.
... The basement of Turkey and Iran is mainly composed of late Neoproterozoic to early Cambrian granitoids. Several late Neoproterozoicearly Cambrian (Cadomian) and Cambrian-Ordovician terranes were formed during the Pan-African orogeny in Europe Nance et al., 1991;Nance et al., 2010) and in different parts of Turkey such as the ˙I stanbul-Zonguldak Zone, Strandja Zone, eastern Sakarya Zone, Menderes Massif and Taurides and also in Bulgaria, Greece, Iran, and Israel (Göncüoglu, 1997;Candan et al., 2001;Gürsu and Göncüoglu, 2006;Okay et al., 2008;Ustaömer et al., 2005;Yılmaz Ş ahin et al., 2014;Abbo et al., 2015;Beyarslan et al., 2016;Moghadam et al., 2017Moghadam et al., , 2021Karsli et al., 2022;Ö zbey et al., 2022). However, it seems that the early Paleozoic rocks in Turkey and Iran show some differences; e.g., I-type and S-type granitoids are present in Turkey, but Ordovician magmatism in Central Iran is dominated by the occurrence of minor mafic alkaline to continental tholeiitic-type igneous rocks. ...
... with the more gradual process of crustal thickening (e.g., Sundell et al., 2022). In this vein, 80 and 72 Ma zircon U-Pb age peaks whose magnitude of crustal contamination decreases through time (Figure 6b) could reflect the combined effects of magmatic assimilation of Neoproterozoic and Paleozoic Pontide basement assemblages (Şengör et al., 1984;A. Ustaömer et al., 2005;T. Ustaömer et al., 2013) during slab rollback and southward arc migration (Ocakoğlu et al., 2018). Thus, documented uplift and subaerial exposure of the İzmir-Ankara accretionary prism in Campanian times, evidenced by increasing Ni/Zr ratios (Ocakoğlu et al., 2018) could be reconciled by topographic doming as a result of southward arc m ...
The number of subduction zones that facilitated the northward translation of the
Anatolide-Tauride continental terrane derived from Gondwana to the southern margin of Eurasia at the longitude of western Turkey is debated. We hypothesized that if two north dipping subduction zones facilitated incipient collision in western Turkey, a late Cretaceous arc would have formed within the Neotethys and along the southern margin of Eurasia. To determine if an island arc formed within the Neotethys we investigated the sedimentary record of the Central Sakarya basin, which was deposited along the southern margin of Eurasia from 85 to 45 million years ago. Detrital zircon deposited within the lower levels of the Central Sakarya basin (the Değirmenözü Formation) are associated with south to north-directed paleocurrents and exhibit a unimodal late Cretaceous age peak sourced from isotopically juvenile mantle melts. Zircon maximum depositional ages from the Değirmenözü Formation cluster between 95 and 90 Ma and are 5–10 Myr older than biostratigraphic depositional ages. Between 95 and 80 Ma, a 12-unit shift from mantle to crustal derived εHf values occurs in the overlying Yenipazar Formation. We explain the absence of Paleozoic, Eurasian-sourced detrital zircon, the rapid shift from mantle to crustal derived εHf values, and lag time in terms of passive margin subduction within an isolated intra-oceanic subduction zone, whose island arc was reworked from south to north into the Central Sakarya basin during incipient collision. Thus, widely outcropping late Cretaceous plutonic rocks within Eurasia must have belonged to an additional convergent margin.
... The volcanoclastic rocks are mostly turbidites with huge exotic blocks. The neotectonic Miocene sedimentary cover of the eastern part of the İstanbul Terrain comprises dominantly fluvio-lacustrine sediments and overlies the Eocene rocks with an erosional contact (Okay et al., 1994;Görür, 1997;Ustaömer et al., 2005;Okay, 2008;Hippolyte et al., 2016;Tüysüz, 2022). ...
Favourable conditions for geothermal energy were created in Turkey during its neotectonic episode from Neogene to Quaternary. This episode is characterized mainly by fluvio-lacustrine sedimentation and strike-slip tectonics with associated magmatism. Under these conditions, a great number of geothermal areas have formed in the neotectonic provinces in association with major tectonic features, including the North and East Anatolian Fault Zones (NAFZ and EAFZ, respectively). Today, the geothermal resources of Turkey are mainly located in the West Anatolian Extensional Province associated with the graben systems. However, the Central Anatolian Ova Neotectonic Province is considered as one of the most promising geothermal targets which are characterized by the presence of widespread hot dry rock systems. This study mainly aims to throw light on the possible potentiality of these resources at Kırşehir Block by emphasizing the neotectonic evolution of the country.
... The main difference between these two tectonic units, separated by the Intra-Pontide Suture (Fig. 1B), lies in their pre-Jurassic stratigraphy. The ˙I stanbul Zone is an Avalonia-type terrain that is characterized by an upper Neoproterozoic crystalline basement (Ustaömer et al., 2005;Bozkurt et al., 2008;Okay et al., 2008;Okay and Nikishin, 2015) and an overlying Paleozoic sedimentary succession (e. g., Görür et al., 1997;Ö zgül, 2012). On the other hand, the Sakarya Zone shows affinity to Armorican terrains with its Carboniferous plutonism (and related high temperature metamorphism) and metamorphosed lower Paleozoic sequences Nikishin et al., 2015;Okay and Topuz, 2017;Topuz et al., 2019). ...
The Late Jurassic–Early Cretaceous is an interval of unstandardized stages and includes the only Mesozoic system boundary without a Global Boundary Stratotype Section and Point – the Jurassic/Cretaceous (J/K) boundary. Recent researches have been mainly focused on deep marine continuous successions from the Tethyan region and provided important progress in calibration of pelagic bioevents. Correlation of these pelagic zonations with the schemes from shallow marine deposits is still obscure. Biostratigraphical data from marginal carbonates containing fossils both from the platform and basinal facies can provide the required links between these two distinct depositional environments. This kind of Upper Jurassic–Lower Cretaceous carbonates widely crop out in the Pontides (northern Turkey) in close association with related shallow and deep marine successions. A biostratigraphical dataset including 17 stratigraphical sections from this Pontides Carbonate Platform is synthesized. The fossil data include organisms from various depositional environments (i.e., benthic and planktonic foraminifers, calpionellids, algae, microencrusters and crinoids) and provides 139 bioevent datums (stratigraphic levels). This fossil dataset is analyzed through the methods of Graphic Correlation (GC) and Unitary Associations (UA) in order to overcome facies (past depositional conditions) controlled local biohorizons and calibrate fossil datums from unrelated phylogenies. Calibration of the Pontides Composite Reference Section (CSRS) with the Geological Time Scale (2020) reveals relative positions of both shallow and deep marine bioevents with respect to the Oxfordian–Hauterivian stage boundaries. The Tithonian/Berriasian and the Berriasian/Valanginian boundaries can be easily delineated by calpionellid bioevents in pelagic successions. However, no synchronous shallow marine first/last occurrence bioevents are available for both of these levels. Increased rates of originations toward Berriasian provide clustering of bioevents around the Tithonian/Berriasian boundary and brackets for both pelagic and shallow marine deposits. Several last occurrences provide unreliable approximations for the Berriasian/Valanginian boundary in neritic deposits. The species richness declines mid-Berriasian onward in accordance with the general trend toward lower sea levels through the late Tithonian into the Valanginian that diminished shallow marine factories and paved the way for a general Valanginian–Hauterivian drowning phase for the Tethyan carbonate platforms. This also adds difficulties in finding reliable origination events in the shallow marine environments for this extinction dominated interval.
... 3b). This combination marks the important fore-arc setting proposed by Zurbriggen (2015;Point #3;Ustaömer et al. 2005). Such bimodal magma sourcing can be associated with a segment of the late Cadomian active margin (earliest Cambrian). ...
In the Balkans, the Serbo-Macedonian Unit (SMU), Serbia, is thrust bounded by the composite Tethyan Vardar Zone and the Carpatho-Balkanides. The SMU actually emerges from beneath the Neoalpine Miocene–Pliocene deposits. Both provenance and geodynamic position of the SMU are poorly known and still debated. This paper reviews the data hitherto published and includes some new field data interpretations. The SMU is composed of a Neoproterozoic–Cambrian high-grade (para- and ortho-) gneiss with peraluminous magmatic arc components (560–470 Ma). The SMU is in the contact with Neoproterozoic upper Ordovician–Carboniferous low-grade metasedimentary succession of an accretionary wedge assembly represented by the Supragetic basement. The SMU basement became folded, sheared and metamorphosed around 490–450 Ma. Paleomagnetic data point to high southern latitudes and a peri-Gondwanan position of the SMU at that time, which concurs with glaciomarine evidence recorded from the upper Ordovician sediments at the base of an accretionary wedge succession. Based on the published data and field survey in the Stalać region, we correlate the SMU with the pre-Mesozoic gneiss terrane exposed in the Strona-Ceneri zone of the Alps. This terrane, identified as the Cenerian orogen of the Alaskan subduction type, developed at an active margin of Gondwana during middle Ordovician times. The SMU basement, with augen and migmatitic gneisses and arc-related peraluminous magmatic bodies, developed at this margin as part of the Cenerian belt or its equivalent. Such an orogenic edifice proved transient and in the earliest Silurian the SMU fragments drifted away being bound for Baltica (amalgamated Moesian microplate and Danubian terrane) to which they became accreted in the Carboniferous and included in the southern European branch of the Variscan orogen (Marginal Dacides/Carpatho-Balkanides). Despite considerable Variscan and Alpine reworking, the pre-Variscan, Cenerian-type crustal assembly along with an inferred boundary between the magmatic arc and the accretionary wedge, accompanied by back-arc/forearc deposits, are still decipherable in the Western Balkan countries.
... This, in turn, is unconformably overlain by a very thick (up to c. 4000 m), variably deformed succession of dominantly siliciclastic sedimentary rocks, mainly conglomerates, sandstone turbidites and mudstones, forming the Late Eocene-Late Miocene Kythrea (Degȋrmenlik) Group ( Fig. 6) (Baroz 1979;Hakyemez et al. 2000;McCay & Robertson 2012;. The intact succession ends with Messinian evaporites and was followed by southward-directed thrusting during latest Cretaceous-earliest Pliocene time, which was related to regional (Bozkurt et al. 1993;Guiraud et al. 2001;Yiǧitbaşet al. 2004;Ustaömer et al. 2005); Paleozoic cover (Göncüoglu & Kozlu 2000 ...
Zircons from Late Triassic deep-water sandstone turbidites of the Mamonia Complex (west Cyprus) have prominent Ediacaran–Cryogenian and Tonian–Stenian age populations, with smaller populations at c. 2.0 and 2.7–2.5 Ga, but only minor concordant Paleozoic zircons. Late Jurassic–Early Cretaceous deep-water gravity-deposited sandstone, also from the Mamonia Complex, has a greater proportion of Ediacaran–Cryogenian and Tonian–Stenian zircons, but less abundant Paleoproterozoic, Archean and Paleozoic zircons. Similar zircon populations characterize an Early Cretaceous shallow-marine sandstone block in the Moni Melange (southern Cyprus). The dominant Ediacaran–Cryogenian and Tonian–Stenian zircon populations originated in the NE Africa/Arabian–Nubian Shield (north Gondwana). However, they were probably recycled from Paleozoic sandstones within Anatolia following South Neotethyan rifting, which also gave rise to sparse Permian–Triassic zircons. Paleozoic zircons reflect Variscan magmatism within Anatolia. Both Late Cretaceous and overlying Eocene sandstone turbidites in the Kyrenia Range (north Cyprus) contain prominent Ediacaran–Cryogenian populations, together with small Archean, Tonian, Carboniferous and Late Cretaceous populations, with additional Triassic zircons in the Eocene sample. Late Cretaceous zircons dominate an overlying Late Miocene sandstone turbidite, together with minor Ediacaran–Cryogenian, Eocene and Miocene populations. The Late Cretaceous zircons record continental margin arc and/or ophiolite-related magmatism, whereas the Eocene and Miocene zircons represent collision-related magmatism, both located in southern Turkey.
Supplementary materials : Detailed zircon U–Pb geochronological data and supplementary figures are available at https://doi.org/10.6084/m9.figshare.c.4483736
... 599-500 Ma) is reported from Central Iran, Sanandaj-Sirjan Zone, NE Iran and even Alborz (Ramezani and Tucker, 2003;Hassanzadeh et al., 2008;Jamshidi Badr et al., 2013;Rossetti et al., 2015;Shafaii Moghadam et al., 2015; this study). The Cadomian magmatic rocks are also recorded from Turkey (570-530 Ma, Gürsu and Göncüoglu, 2006;Okay et al., 2008;Ustaömer et al., 2005Ustaömer et al., , 2009Ustaömer et al., , 2012), and from SW and central Europe, including Iberia and Buhemia (Genna et al., 2002;Murphy et al., 2002;Mushkin et al., 2003). The subduction seems to be started >600 Ma in Europe but the geochronological data support the subduction initiation at ~570 in eastern Gondwana including Turkey and Iran (Linnemann and Romer, 2002;Shafaii Moghadam et al., 2017). ...
Cadomian magmatism is interpreted to indicate fragments of late Neoproterozoic-early Cambrian continental arcs bordering the northern margin of Gondwana. Cadomian rocks constitute the main elements of the continental crust of central Iranian block (including
the Lut block). An example of such Cadomian rocks from NE Iran is studied here: the Dehzaman igneous rocks within the Kashmar- Kerman Tectonic Zone (KKTZ). The Cadomian exposure in NE Iran includes intrusive rocks with a thick sequence of felsic
volcanic rocks. Zircon U-Pb dating of syenogranites and ryholites yielded 238U/206Pb crystallization ages of ≈521.3 to ≈524.3 Ma, respectively and the age of 557 Ma to biotite-syenogranites
already was obtained by Rossetti et al. (2015) (Ediacaran-Early Cambrian).
Geochemically, the intrusive rocks are mostly characterized by high-K content and are similar to the I-type granites. These rocks are characterized by enrichment in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) along with depletion in high field strength elements (HFSEs). Their initial εNd (t) ranges from -0.6 to -2.1 at 86Sr/87Sr (i)=0.7045-0.7073. The Cadomian rocks from NE Iran, along with similaraged rocks from Turkey and Iran are suggested to form in an early stage of an active continental margin.
... 599-500 Ma) is reported from Central Iran, Sanandaj-Sirjan Zone, NE Iran and even Alborz (Ramezani and Tucker, 2003;Hassanzadeh et al., 2008;Jamshidi Badr et al., 2013;Rossetti et al., 2015;Shafaii Moghadam et al., 2015; this study). The Cadomian magmatic rocks are also recorded from Turkey (570-530 Ma, Gürsu and Göncüoglu, 2006;Okay et al., 2008;Ustaömer et al., 2005Ustaömer et al., , 2009Ustaömer et al., , 2012), and from SW and central Europe, including Iberia and Buhemia (Genna et al., 2002;Murphy et al., 2002;Mushkin et al., 2003). The subduction seems to be started >600 Ma in Europe but the geochronological data support the subduction initiation at ~570 in eastern Gondwana including Turkey and Iran (Linnemann and Romer, 2002;Shafaii Moghadam et al., 2017). ...
Cadomian magmatism is interpreted to indicate fragments of late Neoproterozoic-early
Cambrian continental arcs bordering the northern margin of Gondwana. Cadomian rocks
constitute the main elements of the continental crust of central Iranian block (including
the Lut block). An example of such Cadomian rocks from NE Iran is studied here: the
Dehzaman igneous rocks within the Kashmar- Kerman Tectonic Zone (KKTZ). The
Cadomian exposure in NE Iran includes intrusive rocks with a thick sequence of felsic
volcanic rocks. Zircon U-Pb dating of syenogranites and ryholites yielded 238U/206Pb
crystallization ages of ≈521.3 to ≈524.3 Ma, respectively and the age of 557 Ma to biotite-syenogranites already was obtained by Rossetti et al. (2015) (Ediacaran-Early Cambrian).
Geochemically, the intrusive rocks are mostly characterized by high-K content and are
similar to the I-type granites. These rocks are characterized by enrichment in large ion
lithophile elements (LILEs) and light rare earth elements (LREEs) along with depletion
in high field strength elements (HFSEs). Their initial εNd (t) ranges from -0.6 to -2.1
at 86Sr/87Sr (i)=0.7045-0.7073. The Cadomian rocks from NE Iran, along with similaraged
rocks from Turkey and Iran are suggested to form in an early stage of an active
continental margin.
... Prior to the 1990s the "massif"s of Turkey were believed to be of Paleozoic age (Yılmaz, 1991;Yazgan, 1984;Özgül, 1976). However, recent studies (Candan et al., 2011;Oberhansli et al., 2010;Bozkurt et al., 2008;Bozkurt et al., 2006;Anders et al., 2006;Ustaömer et al., 2005;Gessner et al., 2004;Oberhansli et al., 1997;Bozkurt et al., 1993) on the geology of Turkey show that the so called "massif"s are not Paleozoic as a whole and that they have Neoproterozoic cores. Therefore, it is reasonable to assume that they may include economic deposits formed in Precambrian geological environments, i.e. ...
This research investigates the mineralogy and geochemistry of hematite-mica schist of Malatya, Eastern Taurid, and compares the schist with Banded Iron Formations. Banded Iron Formations (BIFs) occur in the Precambrian sedimentary (Superior Type) and volcano sedimentary (Algoma Type) successions. The Hematite Mica Schist (HMS) of Malatya is exposed as a thrust slice between the Permian Malatya Metamorphics and the Eocene Maden Complex and probably as a portion of the Neoproterozoic-Paleozoic Pütürge Massif. The HMS is composed of laminae of quartz, mica-disthene (kyanite) and specular hematite. The Fe2O3 contents of the HMS (>20 %) and the Al2O3 contents (average 22 %), are different from those of Proterozoic BIFs. The TiO2, K2O, MgO, CaO and Na2O contents are much higher than BIFs and average crust values, indicating detrital origin. Trace element and V, Sr, Y, Zr, Nb and Ba contents are higher than in BIF s. Total REE contents of the HMS are much higher than those of BIFs of Proterozoic age and the LREE concentrations are significantly higher than HREE concentrations, both of these indicators can be taken as evidence of detrital origin. Malatya HMS show strong positive Eu anomalies (Eu/Eu*=0.99-1.03) probably originating from a detrital feldspar contribution. The Ce anomalies (Ce/Ce*= 0.003-0.06) of HMS are low positive, indicating a low oxidation state. Data obtained from the studies suggest that the HMS was formed in a sedimentary basin with a low oxidation state, high detrital contribution, low or no hydrothermal contribution. Similar iron formations were deposited in the sequences of glaciomarine settings during the Neoproterozoic. Banded Iron Formations (BIFs ) are not known in Anatolian geologic environment and the HMS of Malatya constitute evidence resembling Neoproterozoic BIF s. Recent studies on the geology of Turkey show that the
so called “massif”s are not Paleozoic as a whole and that they have Neoproterozoic cores. Therefore, it is reasonable to assume that they may include economic deposits formed in Precambrian geological environments, i.e. Banded Iron Formations.
Key words: Hematite mica schist, Banded iron formations, Neoproterozoic, Taurids- Turkey, Pütürge Massif
... The reported isotopic age data from the eastern part of İstanbul Zone, revealed Ediacaran magmatic activity related to subduction (Ustaömer, Mundil, & Renne, 2005). Detrital zircon ages from Lower Ordovician quartzite of Aydos Formation showed a large age span with dominance of Neoproterozoic zircon ages (around 540, 570, 600-640 and 700-800 Ma: all Pan-African) (Ustaömer, Ustaömer, Gerdes, & Zulauf, 2011). ...
... Continuous non-metamorphic Palaeozoic sedimentary successions are found in the Istanbul Zone (Western Pontides) and in the Taurides. In both areas, the Palaeozoic successions are underlain by a Pan-African type Neoproterozoic basement, dated to 590-560 Ma, as shown by Chen et al. (2002) and Ustaömer et al. (2005) for the Istanbul Zone and by Gürsu and Göncüoğlu (2008) for the Taurides. Although these areas have the same basement, their palaeogeographical positions during the entire Palaeozoic are a matter of discussion. ...
Non-metamorphic Palaeozoic sedimentary successions without major breaks exist in the Istanbul Zone of the Western Pontides (northern Turkey) and in the Taurides (southern Turkey). Based on different proxies, a Gondwanan affinity has been determined for the Taurides; however, the palaeogeographical position of the Istanbul Zone is still controversial. The aim of this paper is to discuss possible contributions of late Silurian and Devonian ostracods to the palaeogeographical assignment of the Western Pontides (Istanbul Zone). Furthermore, ostracods of the Taurides have also been evaluated in terms of the palaeogeographical setting of this terrane. Late Silurian ostracods of the Istanbul Zone (Western Pontides) show close similarities at the species level with the assemblage from the upper Silurian (Ludlow) rocks of Baltica. This Laurussian affinity indicates a palaeogeographical setting to the north of the Rheic Ocean for the Pontides during the late Silurian. The Devonian ostracod assemblages of both the Taurides and the Istanbul Zone have an affinity to both Laurussia and Gondwana. Therefore, a faunal link should exist during this long period between Laurussia and Gondwana. The faunal link between the two palaeocontinents can be explained on the one hand by a narrow ocean with shallow pathways. On the other hand, a wider ocean with long-shore currents, with broad and shallow shelf areas and/or islands functioning as stepping stones would also allow a faunal link for benthic ostracods.
We provide a thorough review of the literature on peraluminous magmatism of Late Neoproterozoic and Early Palaeozoic (mostly Late Cambrian-Middle Ordovician) age cropping out in many places around the world (SW South Africa, NE Patagonia, NW Argentina, Colombia, SE Mexico and Guatemala, the European Variscan Massifs and from Turkey to northern Burma through Tibet). Petrographically, these volcanic and plutonic rocks contain K-feldspar phenocrysts and sometimes smaller bluish-quartz phenocrysts in a glassy/fine-grained (volcanic/subvolcanic) or medium- to coarse-grained (plutonic) matrix of quartz, plagioclase, K-feldspar and biotite, with other Al-bearing phases such as muscovite and garnet as minor phases. Notably, amphibole is conspicuously absent. Geochemically, these dacitic (tonalitic) to rhyolitic (granitic) rocks are silica-rich, peraluminous and with a strongly crustal Sr-Nd isotopic signature, pointing to S-type magmatism, but they also show characteristics of I-type subduction (a trace element signature typical of continental-arc magmatism) and A-type (enrichment in Ga) magmatism. A prominent geochemical feature is a marked depletion in Sr, resulting in low to very low Sr/Y ratios (usually <5). This, together with flat HREE slopes, suggests melting at low pressures. The arc signature is inherited from their crustal sources, which may comprise an old crustal basement and sediments derived from Pan-African and from Andean-type orogenic belts. Coeval, volumetrically minor mafic rocks are also common in many outcrops and are part of a bimodal sequence. Researchers have mostly attributed this magmatism to extensional tectonics in a back-arc setting, where the upwelling of the asthenospheric mantle triggered the high-temperature-low-pressure partial melting of a largely metasedimentary (upper continental) crust with little or no contribution from the mantle. In a reconstruction of Early Palaeozoic Gondwana, all outcrops are situated in peri-Gondwanan terranes, implying that they are related to (and the consequence of) rifting processes that led to the opening or aborted opening of several oceans (Rheic, proto-Tethys), reflecting a common evolution of the margin of Gondwana during the Cambrian and Ordovician. Given the similarities in petrography and geochemistry (major and trace elements and Sr-Nd isotopes) and the very large volume, several silicic Large Igneous Provinces have been proposed for some sectors, and the possibility that the entire magmatism comprises a single LIP is evaluated. Although correlations of this magmatism in different regions have been established previously, to our knowledge, this is the first study to integrate detailed petrographic, geochemical and geochronological data from all outcrops and to conclude that the peraluminous porphyritic magmatism reviewed here is the main magmatic expression of extension in the peri-Gondwanan area during the Early Palaeozoic.
The Cimmerian Continent is the narrow continental strip that rifted from the northeastern Gondwana-Land margin mostly during the Permian between the present-day Balkan regions and Indonesia and collided with the Laurasian margin sometime between the latest Triassic and the late Jurassic, in places possibly even in the earliest Cretaceous. In contrast to the initial definition and most subsequent models, the Cimmerian Continent did not leave Gondwana-Land in one piece, but such submarine platforms as the Sakarya, Menderes-Taurus and Kırşehir in Turkey, and what is herein called the Greater Lhasa from Afghanistan to Myanmar began separating both from Gondwana-Land and from the rest of the Cimmerian Continent at about the same time during the Permian. By contrast, the northern part of the Cimmerian Continent remained as a large, single-piece, island arc-type ribbon continent from Turkey to Malaysia comprising the units of the Rhodope-Pontide Fragment in Turkey, most of Transcaucasia and Iran, the Farah, western Qiangtang, Bao-Shan and the Shan States blocks and western Thailand and Malaysia throughout its independent history. This coherent ‘ribbon continent’, perhaps the largest documented in earth history, was almost wholly an ensialic arc only in places having generated Mariana-type ensimatic offspring. Thus, the northern margin of the Cimmerian Continent was of Pacific-type and not Atlantic-type as claimed by many authors in the literature. Naming its various parts individually helps description but should not be allowed to mislead interpretations in terms of individual, so-called ‘terranes’, as often happens. It seems that many of the oceanic basins that opened within and behind the Cimmerian Continent, including the Neo-Tethys, were back-arc basins and the Cimmerian continent had a serpentine motion as it traversed the Tethyan realm. It is therefore impossible to reconstruct synthetic isochrons to track the northerly migration of the large ribbon continent (except for purposes of simple visualisation of the journey of the Cimmerian Continent across the Tethyan realm). The Cimmerian Continent also had a complex internal tectonics, involving much along the strike-slip faulting, presumed to have been controlled by the age, subduction angle, rate of subduction, and the topography of the floor of the Palaeo-Tethys.
The continental crust of Iran is dominated by abundant calc-alkaline and alkaline plutonic and volcanic rocks and by rifted basins filled with mostly terrigenous sedimentary rocks that formed at a Late Ediacaran to Cambrian extensional convergent plate margin along the northern margin of Gondwana. Here we present new zircon U-Pb age, geochemical, and isotopic data from plutonic (granite-granodiorite) and metamorphic (gneiss) rocks in the Kariznou region of NE Iran to provide insights into the nature of the Cadomian convergent margin of Iran. Geochemical data indicate calc-alkaline signatures, characterized by strong depletions in Nb, Ta, P, and Ti and arc-like trace element patterns. New zircon U-Pb ages show that calc-alkaline granitoids and granitic gneiss formed at ~564 to 537 Ma and 538 Ma, respectively. Bulk rock Sr-Nd isotopic data of calc-alkaline rocks have εNd(t) =-5.42 to −5.53 and −6.93 to −7.43 for granite and gneiss, respectively. The gneisses show stronger interaction with and/or re-melting of older continental crust than do granitic rocks. We interpret Kariznou magmatic rocks as forming in association with strong extension accompanied by crustal assimilation. Extension initiated ~570 Ma with the deposition of Late Ediacaran sediments, and magmatism began at 545-535 Ma, generating calc-alkaline magmas. The tectonomagmatic evolution of the Kariznou region encapsulates the prolonged transition of Cadomian Iran from a strongly extensional convergent margin, possibly as a result of oblique oceanic subduction and slab roll-back of the subducting Proto-Tethys oceanic lithosphere, culminating in the formation of an Early Palaeozoic passive margin on the northern side of Gondwana. ARTICLE HISTORY
The Asian continent consists of many continental blocks that assembled during the Phanerozoic, accompanied by widespread granitoids. By compiling a series of digital maps of igneous rocks with associated zircon U-Pb ages and petrological datasets, we illustrate the spatial-temporal evolution of the granitoids, which shed new light on the assembling process of the Asian continent.
Neoproterozoic granitoids in the Central China Orogenic System evolved from deformed S-type (1100–900 Ma) to weakly or undeformed I-, and A-type granites (850–700 Ma), displaying a transition from syncollisional to postcollisional environment along the northern margin of the South China Craton (or Block), corresponding to the assembly and breakup of Rodinia, respectively. Phanerozoic igneous rocks mainly occur in the Central Asian Orogenic Belt (CAOB) and the Tethyan orogenic system, and record the closure processes of ocean systems, i.e., the Paleo-Asian Ocean (PAO), the Mongol-Okhotsk Ocean, and the Tethyan Ocean, as well as marginal processes along the west Paleo-Pacific Ocean (PPO). The assembly of the Asian continent can be summarized into five major stages. (1) Initial formation of the Siberian-Mongol collage in the PAO domain and the East Asian continental assemblage in the Proto-Tethyan domain, which is evidenced by voluminous 550–500 Ma magmatic belts in the northern CAOB and 520–400 Ma belts in the Central China Orogenic System, respectively. (2) Formation of the North Asian continent through the amalgamation of the above two collages following the closure of the PAO (310–250 Ma). The closure occurred in a double scissor-like manner, as indicated by a westward younging trend of granitoids along the western segment (western Tianshan) of the southern CAOB and an eastward younging trend of granitoids along the central and eastern segment (the Solonker-Xilamulun suture zone) of the southern CAOB. (3) Formation of the East Asian continent by 230–210 Ma through the collision of continental blocks/terranes with the North Asian continent. The processes are recorded by several large (> 1500 km-long) Triassic magmatic belts that evolved from subduction (250–230 Ma) to collision (230–220 Ma). (4) Formation of the main Asian continent through the collision between the East Asian and Siberia-Europe continents, following the closure of the Mongol-Okhotsk Ocean by 150 Ma. This closure also occurred in a scissor-like fashion, as evidenced by an eastward younging trend of 230–150 Ma collision-related granitoids along the Mongol-Okhotsk Suture. (5) Final formation of the Asian continent by the terminal suturing of the Meso- and Neo-Tethys and the final collision between the Indian-Arabian continent and Eurasia, marked by a large 130–120 Ma magmatic belt and a 70–4 Ma leucogranite belt in the southern Tethyan Orogenic System. Continental assembly in north Asia (the PAO domain) was associated with oblique collision and terrene rotation, characterized by curved magmatic belts/oroclines and involved a large volume (ca. > 50%) of juvenile crust; whereas continental assembly in south Asia (the Tethyan domain) was characterized by direct collision, characterized by straight linear magmatic belts and involved a smaller (< 5 %) volume of juvenile crust.
We report detrital zircon ages from the Upper Cretaceous (Campanian–Maastrichtian) turbiditic sandstones from the Pontides and the Anatolide–Tauride Block, which were located on opposite margins of the Tethys ocean during most of the Paleozoic and Mesozoic. The large data set includes both published and new detrital zircon ages from the Upper Cretaceous Pontide sandstones (2730 zircon ages from 26 samples) and new detrital zircon ages from the uppermost Cretaceous Bornova Flysch of the Anatolide–Tauride Block (378 ages from five samples). Phanerozoic detrital zircons from the Upper Cretaceous sandstones of the Pontides are predominantly Late Cretaceous (56%) followed by Carboniferous (7.9%), Devonian (5.3%), Jurassic (3.1%) and Triassic (2.9%). In contrast, there are no Cretaceous and Jurassic detrital zircons in the uppermost Cretaceous Bornova Flysch, and the Phanerozoic detrital zircon populations are mainly Carboniferous (41.3%), Triassic (7.1%), Permian (6.9%) and Devonian (5.3%). The absence of Cretaceous and Jurassic zircons in the Bornova Flysch shows that there was no sediment transport between the Pontides and the Anatolide–Tauride Block during the latest Cretaceous (75–70 Ma); it also shows that the latest Cretaceous – Paleocene deformation of the Bornova Flysch Zone predates the collision between the Pontides and the Anatolide–Tauride Block, and is associated with ophiolite obduction. The dominance of Carboniferous detrital zircons in the Bornova Flysch Zone underlines that Carboniferous magmatic activity in the Anatolide–Tauride Block, and hence on the northern margin of Gondwana, was more significant than hitherto recognized.
The study presents geological field observations, petrographic characteristics and bulk rock geochemical data of listwaenitic occurrences related to Jurassic–Cretaceous IAESZ ophiolites of the northern part of Turkey. Listwaenites of the Jurassic–Cretaceous Eldivan ophiolite and the the Cretaceous Dağküplü ophiolite occur as mineralized or non-mineralized blocks and/or veins associated with serpentinized peridotites and ophiolitic mélanges along major thrust zones within the Izmir–Ankara–Erzincan Suture Zone (IAESZ) of the Northern Branch of the Neo-Tethys, Turkey. The silica–carbonate listwaenites (Type I) consist mainly of dolomite and minor calcite with quartz and minor phyllosilicates (chlorite, mica), serpentine and hematite. They are formed by circulation of meteoric hydrothermal fluids, along major décollement faults and thrust faults during the emplacement of serpentinized peridotites. The Kaymaz listwaenites (Type II) are composed mainly of fine-grained microcrystalline quartz with negligible dolomite, calcite, magnesite, serpentine and Fe-hydroxides. They display hard resistant masses, and are adjacent to the Eocene granitic bodies. Listwaenites are gentically related to the serpentinized peridotites, while the mineralization appears to be related to the granite-related hydrothermal fluids.
New U–Pb zircon data from the Kurtoğlu Massif (eastern Sakarya Zone, Turkey) reveal a Cadomian back-arc basin, evolving to closure of the Rheic Ocean. A host metapsammite from the lower tectonic slice of the massif yielded detrital zircon ages ranging from Neoarchean (2.73 Ga) to late Neoproterozoic with a major population between 610 and 553 Ma and a peak at 592 Ma, implying that the basement of the Sakarya Zone has a Cadomian affinity. This metasedimentary sequence was intruded by an orthogneiss in the early Ordovician (481 Ma) probably during the opening of the Rheic Ocean. Zircon grains from the overlying metasedimentary sample yielded concordant ages spreading throughout the Mesoproterozoic (1608–1032 Ma) and early Paleozoic (516–351 Ma), suggesting that they were deposited in the Rheic Ocean likely prior to its final closure. The muscovite metagranite, emplaced into the host rocks of the Kurtoğlu Massif at 388 Ma, formed probably during northward closure of the Rheic Ocean. Zircon grains of a metasiltstone from the upper tectonic slice of the massif, represented mainly by phyllites, yielded similar age spectra to that of the host metapsammite of the lower tectonic slice. Such phyllites in the Pulur Massif ⁓ 35 km to the southeast display a close association with the ophiolitic complexes of the Rheic Ocean. This relationship together with the age spectra mentioned above suggests that sedimentation was on a place away from the Paleozoic igneous sources, in an analogous position to the southern passive margin of the Rheic Ocean.
A combined U-Pb geochronology, whole-rock geochemistry, and Sr-Nd isotopic study give new insights into the nature of the protolith, tectonic setting, and petrogenetic history of Cadomian orthogneisses from the Tutak metamorphic complex (TMC), Sanandaj-Sirjan Zone, Iran. U–Pb zircon dates of 535 ± 4 Ma suggest an Early Cambrian crystallization age for the orthogneiss protoliths. Geochemical data indicate that the orthogneisses have I-type, high-K calc-alkaline, and peraluminous signatures. Depletion in Nb, Ta, Ti, Sr, and enrichment in Nd, Th, K, U relative to the primitive mantle, suggest derivation in a subduction zone environment in an active continental margin. Initial ⁸⁷Sr/⁸⁶Sr and ¹⁴³Nd/¹⁴⁴Nd ratios vary from 0.7045 to 0.7092 and from 0.5116 to 0.5117, respectively. Moreover, εNd(t) values range from − 2.95 to − 5.29, and two-stage model ages vary from 1.4 to 1.6 Ga. Taken together, these data suggest derivation of TMC orthogneisses from a metasomatic lithospheric mantle with a contribution of a crustal component generated via partial melting of a metabasite (i.e., amphibolite).
Cadomian magmatic activity is represented by a mafic – intermediate dyke suits in the Karacahisar dome (West – Central Taurides) formed by the southward subduction of the Proto-Tethyan ocean beneath North Gondwana. These dyke suites are classified as diabase, andesite and dacite. They display calc-alkali, high-K calc-alkali and shoshonitic character, and intruded into the siliciclastic rocks deposited in a back-arc rift setting. In this study, we present new zircon U-Pb ages, Sr-Nd isotopic and geochemical data to better understand the petrological evolution of the Cadomian magmatism. Zircon U-Pb concordia ages of 551.3 ± 3.5 Ma, 557.9 ± 3.7 Ma and 569 ± 7.2 Ma were obtained for these dykes. On the N-MORB normalized spider diagrams, mafic – intermediate dykes exhibit enrichment in large ion lithophile elements (LILE: Sr, K, Rb, Ba, Th), relatively less enrichment in light rare earth elements (LREE: La, Ce and Nd) and depletion in high field strength (HFS: Tb, Ti, Y and Yb) elements. Dyke samples have significant depletions of Ta and Nb relative to neighbouring LILE and LREE and display a significant subduction component. On the chondrite normalized REE diagrams, a weak Eu anomalies are observed, and this indicates some plagioclase accumulation. Dyke samples fall into the volcanic arc (island arc and/or continental arc), and back-arc fields on tectonic setting discrimination diagrams. The εNd(i) values of dykes range from −1.47 to 1.76, and Nd depleted-mantle model (TDM) ages vary between 1.32 and 1.81 Ga, and show enriched mantle or metasomatized subcontinental lithospheric mantle source signatures. The primary magmas of the dykes were derived from amphibole- and garnet-bearing mantle, and were affected by fractional crystallization, mixing and assimilation processes during ascent through the upper crust. All available data show that this magmatic activity developed in a back-arc rift setting subsequent to Cadomian arc magmatism in the West-Central Taurides.
Cadomian (Ediacaran–Cambrian) magmatic rocks have been reported in the eastern (e.g. the Çatalca and İhsaniye plutons) and western (e.g. the Binkılıç and Safaalan plutons) parts of the Istranca (Strandja) Massif. This paper aims to investigate the tectonic setting and the magma evolution history of the Cadomian magmatic rocks using both new and previously existing geochemical and geochronological data. The meta-granitoid rocks with intermediate to felsic composition are the main magmatic activity in the region. They intrude into metamorphic basement rocks composed of gneiss, schist, amphibolite, calc-schist, and quartzites (the Tekedere group). These plutons show strong foliation and traces of the polyphase metamorphism. All plutons are peraluminous and slightly metaluminous, mostly calc-alkaline and high-K calc-alkaline, and plot into the volcanic arc granites (VAG) field on the tectono-magmatic discrimination diagrams. The zircon U–Pb crystallization ages of the plutons are between 525.3 ± 3.5 Ma and 548.7 ± 2.3 Ma. Initial εNd values vary from −0.02 to 1.86. Nd-TDM model ages range between 1.08 and 1.24 Ga and indicate that the primitive magmas were originated and/or assimilated by the remelting of Neoproterozoic juvenile crustal rocks. New geochemical and geochronological data suggest a magma generation within a subduction-related magmatic arc setting in response to the southward subduction of the Proto-Tethys Ocean during the Late Precambrian-Early Palaeozoic period in the Istranca Massif.
The geological evolution of the Proto-Tethys Ocean remains vague. The Tianshuihai Terrane (TSHT), a subterrane of the West Kunlun, distributed to the south of the Proto-Tethys Ocean during the Early Palaeozoic, records abundant information on the geological evolution of the Proto-Tethys Ocean. In this study, we reported SHRIMP and LA-ICP-MS zircon U–Pb ages, whole-rock major and trace element composition data, and Sr-Nd-Hf isotopes of a suite of monzogranites and the monzonitic-syenitic enclaves in Zankan and syenogranites in Laobing regions of the TSHT, West Kunlun Orogenic Belt. The syenogranites in the Laobing region yielded SHRIMP zircon U-Pb ages of 550.4 ± 6.4 Ma to 547.5 ± 5.3 Ma, which were the earliest age records of subduction-related magmatism in the TSHT during the Late Neoproterozoic-Early Palaeozoic. The host monzogranites in the Zankan area yielded SHRIMP and LA-ICP-MS zircon U-Pb ages of 542.6 ± 8.4 Ma to 540.5 ± 2.8 Ma, which is coeval with the monzonitic-syenitic enclaves ages of 533.8 ± 3.4 Ma to 534.7 ± 3.0 Ma. We speculated that an active margin developed along the TSHT during the Cambrian and the initial subduction of the Proto-Tethys oceanic slab must have occurred prior to the Early Cambrian (>550 Ma). The TSHT and the Southern Kunlun Terrane were distributed between the northern margin of the East Gondwana continent and the Tarim Block. Additionally, the coexistence of two branches of the Proto-Tethys Ocean represented by the Kangxiwa Fault and Kudi Ophiolite Belt during the Early Palaeozoic. Based on the chronological statistics of micro-continental blocks in the northern margin of the East Gondwana continent, subduction of the Proto-Tethys Ocean could be diachronous, initially originating in the northwestern part of the East Gondwana continent, and gradually propagating to the east of the East Gondwana continent.
Apatite fission-track and (U-Th)/He ages from Carboniferous to Eocene siliciclastic rocks of the Istanbul Zone (NW Turkey) range from 220 to 46 Ma, and from 46 to 18 Ma, respectively. Apatite grains from the upper Cretaceous and Eocene volcaniclastic and siliciclastic formations yielded unreset fission-track ages (85 to 65 Ma), whereas the Lower Cretaceous siliciclastic rocks yielded both reset and unreset apatite fission-track ages. This suggests the absence of substantial burial after the Early Cretaceous. The thermochronological dataset presented here in conjunction with published data defines three major deformation and uplift/exhumation phases: (i) 220-179 Ma (Late Triassic-Early Jurassic), (ii) 101-107 Ma (mid-Cretaceous), and (iii) 66-16 Ma (Palaeocene-early Miocene). The Late Triassic-Early Jurassic uplift/exhumation phase can be attributed to the Cimmeride orogeny and the uplift of the Pontides. The mid-Cretaceous uplift/deformation is also reflected in the stratigraphic record as a major unconformity, which was probably caused by the accretion of an oceanic plateau or a seamount. The Palaeocene-early Eocene uplift/deformations resulted from the closure of the Izmir-Ankara-Erzincan oceanic domain. The late Oligocene-early Miocene uplift/deformation is probably caused by extension in the Aegean region due to the suction along the Hellenic trench. ARTICLE HISTORY
Apatite fission-track and (U-Th)/He ages from Carboniferous to Eocene siliciclastic
rocks of the Istanbul Zone (NW Turkey) range from 220 to 46 Ma, and from 46 to 18 Ma, respectively. Apatite grains from the upper Cretaceous and Eocene volcaniclastic and
siliciclastic formations yielded unreset fission-track ages (85 to 65 Ma), whereas the Lower Cretaceous siliciclastic rocks yielded both reset and unreset apatite fission-track ages. This suggests the absence of substantial burial after the Early Cretaceous. The thermochronological dataset presented here in conjunction with published data defines three major deformation and uplift/exhumation phases: (i) 220-179 Ma (Late Triassic-Early Jurassic), (ii) 101-107 Ma (mid-Cretaceous), and (iii) 66-16 Ma (Paleocene-early Miocene). The Late Triassic-Early Jurassic uplift/exhumation phase can be attributed to the Cimmeride orogeny and the uplift of the Pontides. The mid-Cretaceous uplift/deformation is also reflected in the stratigraphic record as a major unconformity, which was probably caused by the accretion of an oceanic plateau or a seamount. The Paleocene-early Eocene uplift/deformations resulted from the closure of the Izmir-Ankara-Erzincan oceanic domain. The late Oligocene-early Miocene uplift/deformation is probably caused by extension in the Aegean region due to the suction along the Hellenic trench.
The late Neoproterozoic (Ediacaran) igneous and metamorphic complex that constitutes the main part of the
Precambrian basement in Iran is exposed in southwestern Saqqez in the northern Sanandaj-Sirjan zone (SaSZ),
which is called the Ediacaran complex in this study. New zircon U–Pb dating from five samples shows that the
crystallization of the main granitic bodies happened 559 to 547 Ma in the late Neoproterozoic (Ediacaran). The
Ediacaran complex in southwest Saqqez includes: (a) metarhyolite-sedimentary sequences; (b) metagranite; and
(c) metadiorite-monzonitic bodies with some late stage dikes. Whole-rock compositions of the granites show
high contents of SiO2 (62.9–80.5 wt.%), K2O (0.1–4.0 wt.%), and Al2O3 (9.7–19.1 wt.%) with low contents of
MgO (0.2–2.4 wt.%), Fe2O3 (0.7–6.9 wt.%), and TiO2 (0.1–1.0 wt.%). Negative εNd(t) (−5.2 to −3.0) and high
initial ratios of 87Sr/86Sr (0.7101 to 0.7328) indicate the main role of crustal components in the sources of the
granitic bodies. The metadiorite-monzonitic rocks have high contents of Fe2O3 (6.4–10.7 wt.%), MgO
(6.6–8.1 wt.%), CaO (5.7–9.7 wt.%), and TiO2 (0.4–1.2 wt.%) with positive εNd(t) (+2.9 to +4.4) values. Whole
rocks compositions and 87Sr/86Sr–143Nd/144Nd isotope ratios show different sources for the metagranite and
metadiorite-monzonite groups, which are consistent with continental crust and subcontinental lithospheric
mantle released melts, respectively. The high contents of Th with low contents of the transitional elements such
as Nb-Ta with calc-alkaline affinity of the both intermediate and acidic rocks infer the relation of these rocks to
an active continental margin over the subduction zone in the late Neoproterozoic which is associated with Proto-
Tethys subduction beneath northern Gondwana in that time
The Devrekani Massif in the northern part of the Central Pontides (Northern Turkey) provides important clues to the regional tectonics and geodynamic processes associated with Jurassic high grade metamorphic conditions. This study reports new paragenetic assemblages, mineral compositions, whole-rock geochemistry and 40Ar-39Ar geochronological data from the paragneisses in the massif, and, discusses the P–T conditions and geodynamic implications of the Jurassic metamorphism during continental extension in the Central Pontides. Upper amphibolite to lower granulite facies paragneisses form one of the main lithological units in the massif. Within these, there are five different mineral parageneses with diagnostic mineral assemblages of: quartz, K-feldspar (An0-1Ab4-26Or73-96), plagioclase (An18-35), biotite [XPhl: 0.28–0.57; Mg/(Mg + Fe2+): 0.33–0.61], sillimanite, cordierite [Mg/(Mg + Fe2+): 0.48–0.71] and garnet (Alm43-80Grs0-18Prp5-23And0-4Sps10-33) with minor hercynite. Based on Na-in-Crd thermometry and GASP barometry results, the peak metamorphic conditions are 775 ± 25 °C and 6 ± 1 kbar in the massif. The field relations, petrography and bulk chemical data suggest that the paragneisses, derived from shale-wackestone and pelitic sedimentary protoliths, are typical rock lithologies of an active continental margin. They display enrichments in LILE over HFSE, coupled with negative Nb and Ti anomalies, which are geochemical signatures of subduction-related sources. It is likely that the peak metamorphism took place during the Middle–Upper Jurassic period (ca. 174–156 Ma), suggesting that the metamorphic rocks cooled to 300–350 °C at ca. 156 Ma. The mineral assemblages reveal that the prograde history passed from sillimanite zone conditions up to the cordierite-garnet-K-feldspar zone. The petrological and geochronological data indicate that the protoliths are related to multiple sources such as volcano-sedimentary successions. We conclude that the Devrekani Massif represents the products of pre-Jurassic sedimentation, and Permo-Carboniferous continental arc magmatism, overprinted by Jurassic metamorphism.
The Armutlu peninsula is a composite tectonic entity made up of sections of the Sakarya continent, the Rhodope-Pontide fragment and an ophiolite. These were assembled following a continental collision between Gondwanaland and Laurasia during the Late Cretaceous. The northern margin of the Sakarya continent underwent progressively increasing deformation prior to and during the advancing collision, due to continued convergence between the two continents. Initially, the leading edge of the continent subsided under the load of an approaching ophiolitic slab. Following this, a north-directed thrusting and folding occurred during the Turonian.Progressive elimination and eventual closure of the ocean preceded the thrusting of northerly situated, collisiondashinduced, nappe packages over the leading edge of the Sakarya continent. The nappe-laden edge of the continental margin then collapsed and steadily subsided under the heavy load of the ophiolitic slab and the northern continental fragment. Consequently, the nappe packages and the ophiolite were collectively metamorphosed during the ConiaciandashSantonian interval. During the subsidence the main body of the Sakarya continent partially detached from its collapsed edge along a fault zone and thus suffered an independent but less severe deformation, which lasted until the uplift of the collapsed edge in the Campanian. From the late Campanian onward, throughout later orogenic stages, the metamorphic and nondashmetamorphic units amalgamated into a single tectonic entity, forming a basement for younger cover rocks.
The Tethyan evolution of Turkey may be divided into two main phases, namely a Palaeo-Tethyan and a Neo-Tethyan, although they partly overlap in time. The Palaeo-Tethyan evolution was governed by the main south-dipping (present geographic orientation) subduction zone of Palaeo-Tethys beneath northern Turkey during the Permo-Liassic interval. During the Permian the entire present area of Turkey constituted a part of the northern margin of Gondwana-Land. A marginal basin opened above the subduction zone and disrupted this margin during the early Triassic. In this paper it is called the Karakaya marginal sea, which was already closed by earliest Jurassic times because early Jurassic sediments unconformably overlie its deformed lithologies. The present eastern Mediterranean and its easterly continuation into the Bitlis and Zagros oceans began opening mainly during the Carnian—Norian interval. This opening marked the birth of Neo-Tethys behind the Cimmerian continent which, at that time, started to separate from northern Gondwana-Land. During the early Jurassic the Cimmerian continent internally disintegrated behind the Palaeo-Tethyan arc constituting its northern margin and gave birth to the northern branch of Neo-Tethys. The northern branch of Neo-Tethys included the Intra-Pontide, Izmir—Ankara, and the Inner Tauride oceans. With the closure of Palaeo-Tethys during the medial Jurassic only two oceanic areas were left in Turkey: the multi-armed northern and the relatively simpler southern branches of Neo-Tethys. The northern branch separated the Anatolide—Tauride platform with its long appendage, the Bitlis—Pötürge fragment from Eurasia, whereas the southern one separated them from the main body of Gondwana-Land. The Intra-Pontide and the Izmir—Ankara oceans isolated a small Sakarya continent within the northern branch, which may represent an easterly continuation of the Paikon Ridge of the Vardar Zone in Macedonia. The Anatolide-Tauride platform itself constituted the easterly continuation of the Apulian platform that had remained attached to Africa through Sicily. The Neo-Tethyan oceans reached their maximum size during the early Cretaceous in Turkey and their contraction began during the early late Cretaceous. Both oceans were eliminated mainly by north-dipping subduction, beneath the Eurasian, Sakaryan, and the Anatolide- Tauride margins. Subduction beneath the Eurasian margin formed a marginal basin, the present Black Sea and its westerly prolongation into the Srednogorie province of the Balkanides, during the medial to late Cretaceous. This resulted in the isolation of a Rhodope—Pontide fragment (essentially an island arc) south of the southern margin of Eurasia. Late Cretaceous is also a time of widespread ophiolite obduction in Turkey, when the Bozkir ophiolite nappe was obducted onto the northern margin of the Anatolide—Tauride platform. Two other ophiolite nappes were emplaced onto the Bitlis—Pötürge fragment and onto the northern margin of the Arabian platform respectively. This last event occurred as a result of the collision of the Bitlis—Pötürge fragment with Arabia. Shortly after this collision during the Campanian—Maastrichtian, a subduction zone began consuming the floor of the Inner Tauride ocean just to the north of the Bitlis—Pötürge fragment producing the arc lithologies of the Yüksekova complex. During the Maastrichtian—Middle Eocene interval a marginal basin complex, the Maden and the Çüngüş basins began opening above this subduction zone, disrupting the ophiolite-laden Bitlis—Pötürge fragment. The Anatolide-Tauride platform collided with the Pontide arc system (Rhodope—Pontide fragment plus the Sakarya continent that collided with the former during the latest Cretaceous along the Intra Pontide suture) during the early to late Eocene interval. This collision resulted in the large-scale south-vergent internal imbrication of the platform that produced the far travelled nappe systems of the Taurides, and buried beneath these, the metamorphic axis of Anatolia, the Anatolides. The Maden basin closed during the early late Eocene by north-dipping subduction, synthetic to the Inner-Tauride subduction zone that had switched from south-dipping subduction beneath the Bitlis—Pötürge fragment to north dipping subduction beneath the Anatolide—Tauride platform during the later Palaeocene. Finally, the terminal collision of Arabia with Eurasia in eastern Turkey eliminated the Çüngüş basin as well and created the present tectonic regime of Turkey by pushing a considerable piece of it eastwards along the two newly-generated transform faults, namely those of North and East Anatolia. Much of the present eastern Anatolia is underlain by an extensive mélange prism that accumulated during the late Cretaceous—late Eocene interval north and east of the Bitlis—Pötürge fragment.
Pan-African basement rocks and the Palaeozoic cover series of the Menderes Massif are exposed around Derbent (Alaflehir) in the eastern part of the Ödemifl-Kiraz submassif. Garnet-mica schists of the Pan-African basement are intruded by the protoliths of orthogneisses and Triassic leucocratic orthogneisses. This study focuses on the geochronology and geochemistry of orthogneisses related to the Pan-African evolution of the Menderes Massif in latest Proterozoic time. Geochemical data suggest that the orthogneisses were derived from S-type, peraluminous, syn- to post-collisional granitoids of calc-alkaline affinity. Zircon grains from the orthogneisses, which are euhedral with typical igneous morphologies, were dated by the Pb-Pb evaporation method. Single zircon ages of two samples yielded 207 Pb/ 206 Pb ages of 561.5-1.8 Ma and 570.5-2.2 Ma. These ages are interpreted as the time of protolith emplacement of the orthogneisses. This major magmatic episode of the Menderes Massif can be attributed the Pan-African Orogeny which was related to the closure of the ocean basins and amalgamation of East and West Gondwana. ortalama 561.5-1.8 my ve 570.5-2.2 my olarak elde edilmifltir. Bu yafllar ortognayslar›n ilksel kayalar›n›n sokulum yafl› olarak yorumlanm›flt›r. Menderes Masifi'ndeki bu ana magmatik olay okyanus havzalar›n›n kapanmas› ve Dou ve Bat› Gondvana'n›n çarp›flmas›na balant›l› Pan-Afrikan orojeneziyle iliflkilendirilebilir.
Despite extensive reworking in Devonian and Carboniferous times, two major deformational events taking place in late Precambrian times may be recognized in the SW Iberian Massif. These have been collectively referred to as ‘Cadomian’ or ‘Pan-African’. The Precambrian successions may be subdivided into pre-orogenic and syn-orogenic groups on the basis of their tectonostratigraphic evolution with respect to the Cadomian orogeny. The pre-orogenic successions (roughly mid-upper Riphean) represent different parts of a miogeoclinal wedge, the basement of which is not known as yet. Polyphase deformation and variable degrees of metamorphism accompanied the first Cadomian event.
The syn-orogenic successions (roughly upper Riphean-Vendian) were laid down during and after the first Cadomian event and were in turn deformed and slightly metamorphosed by the second single-phased deformation. These correspond to two distinct types: calc-alkaline igneous successions and flysch-like deposits, that can be interpreted respectively as an orogenic continental arc suite and a foreland basin fill, on the basis of their geochemical and sedimentological characteristics.
Diachronous subsidence patterns of Tethyan margins since the Early Palaeozoic provide constraints for paleocontinental reconstructions and the opening of disappeared oceans. Palaeotethys opening can be placed from Ordovician to Silurian times and corresponds to the detachment of a ribbon-like Hun Superterrane along the Gondwanan margin. Neotethys opening took place from Late Carboniferous to late Early Permian from Australia to the eastern Mediterranean area. This opening corresponds to the drifting of the Cimmerian superterrane and the final closing of Palaeotethys in Middle Triassic times. Northward subduction of Palaeotethys triggered the opening of back-arc oceans along the Eurasian margin from Austria to the Pamirs. The fate of these Permo-Triassic marginal basins is quite different from areas to area. Some closed during the Eocimmerian collisional event (Karakaya, Agh-Darband), others (Meliata) stayed open and their delayed subduction induced the opening of younger back-arc oceans (Vardar, Black Sea). The subduction of the Neotethys mid-ocean ridge was certainly responsible for a major change in the Jurassic plate tectonics. The Central Atlantic ocean opened in Early Jurassic time and extended eastwards into the Alpine Tethys in an attempt to link up with the Eurasian back-arc oceans. When these marginal basins started to close the Atlantic system had to find another way, and started to open southwards and northwards, slowly replacing the Tethyan ocean by mountain belts.
The Teplá – Barrandian unit (TBU) of the Bohemian Massif shared a common geological history throughout the Neoproterozoic and Cambrian with the Avalonian – Cadomian terranes. The Neoproterozoic evolution of an active plate margin in the Teplá – Barrandian is similar to Avalonian rocks in Newfoundland, whereas the Cambrian transtension and related calc-alkaline plutons are reminiscent of the Cadomian Ossa – Morena Zone and the Armorican Massif in western Europe. The Neoproterozoic evolution of the Teplá – Barrandian unit fits well with that of the Lausitz area (Saxothuringian unit), but is significantly distinct from the history of the Moravo – Silesian unit. The oldest volcanic activity in the Bohemian Massif is dated at 609+17/À19 Ma (U – Pb upper intercept). Subduction-related volcanic rocks have been dated from 585F7 to 568F3 Ma (lower intercept, rhyolite boulders), which pre-dates the age of sedimentation of the Cadomian flysch (Š těchovice Group). Accretion, uplift and erosion of the volcanic arc is documented by the Neoproterozoic Dobříš conglomerate of the upper part of the flysch. The intrusion age of 541+7/À8 Ma from the Zgorzelec granodiorite is interpreted as a minimum age of the Neoproterozoic sequence. The Neoproterozoic crust was tilted and subsequently early Cambrian intrusions dated at 522F2 Ma (Těšovice granite), 524F3 Ma (Všepadly granodiorite), 523F3 Ma (Smržovice tonalite), 523F1 Ma (Smržovice gabbro) and 524F0.8 Ma (Orlovice gabbro) were emplaced into transtensive shear zones. D 2002 Elsevier Science B.V. All rights reserved.
The Strandja Massif is a mid-Mesozoic orogenic belt in the Balkans build on a late-Variscan basement of gneisses, migmatites and granites. New single-zircon evaporation ages from the gneisses and granites indicate that the high-grade metamorphism and plutonism is Early Permian in age (~271 Ma). The late-Variscan basement was unconformably overlain by a continental to shallow marine sequence of Early Triassic-Mid-Jurassic age. During the Late Jurassic-Early Cretaceous (Oxfordian-Barremian) the lower Mesozoic cover and the basement were penetratively deformed and regionally metamorphosed in greenschist facies possibly due to a continental collision. An Rb-Sr biotite whole-rock age from a metagranite dates the regional metamorphism as Late Jurassic (155 Ma). Deformation involved north-vergent thrust imbrication of the basement and the emplacement of allochthonous deep marine Triassic series over the Jurassic metasediments. The metamorphic rocks of the Strandja Massif are unconformably overlain by the Cenomanian shallow marine sandstones. During the Senonian, the northern half of the Strandja Massif formed a basement to an intra-arc basin and to a magmatic arc generated above the northward-subducting Tethyan oceanic lithosphere. The Srednogorie arc closed during the early Tertiary through renewed northward thrusting of the Strandja Massif.
Pre-Variscan basement elements of Central Europe appear in polymetamorphic domains juxtaposed through Variscan and/or Alpine tectonic events. Consequently, nomenclatures and zonations applied to Variscan and Alpine structures, respectively, cannot be valid for pre-Variscan structures. Comparing pre-Variscan relics hidden in the Variscan basement areas of Central Europe, the Alps included, large parallels between the evolution of basement areas of future Avalonia and its former peri-Gondwanan eastern prolongations (e.g. Cadomia, Intra-Alpine Terrane) become evident. Their plate-tectonic evolution from the Late Proterozoic to the Late Ordovician is interpreted as a continuous Gondwana-directed evolution. Cadomian basement, late Cadomian granitoids, late Proterozoic detrital sediments and active margin settings characterize the pre-Cambrian evolution of most of the Gondwana-derived microcontinental pieces. Also the Rheic ocean, separating Avalonia from Gondwana, should have had, at its early stages, a lateral continuation in the former eastern prolongation of peri-Gondwanan microcontinents (e.g. Cadomia, Intra-Alpine Terrane). Subduction of oceanic ridge (Proto-Tethys) triggered the break-off of Avalonia, whereas in the eastern prolongation, the presence of the ridge may have triggered the amalgamation of volcanic arcs and continental ribbons with Gondwana (Ordovician orogenic event). Renewed Gondwana-directed subduction led to the opening of Palaeo-Tethys.
The pre-Alpine basement of eastern Crete consists of at least three sub complexes which show differences in age and grade of pre-Alpine metamorphism. U-Pb analyses of zircons of two orthogneisses yielded upper intercepts in the concordia diagram at 51116Ma (Chamez crystalline complex) and 51414Ma (Myrsini crystalline complex). These values are interpreted as protolith ages of the gneisses, suggesting that parts of the basement underwent Cadomian (Pan-African) imprints at the northern margin of Gondwana. The lower intercept ages are attributed to Alpine subduction which led to high-pressure/low-temperature metamorphism (T=ca. 300C), brittle-ductile deformation, and hydrothermal fluid activity. Due to pervasive Alpine fluid migration, the zircons of the Chamez crystalline complex display disturbed zonation and solution, resulting in 87% radiogenic Pb loss, Ca- and Al-gain, and Zr depletion.
The West Pontides tectonic belt of northern Turkey comprises a Lower Ordovician–Lower Carboniferous transgressive sequence.
A stratigraphic basement to this Paleozoic sequence is exposed in the Bolu area. The tectono-stratigraphy of the basement
closely resemble that of the Cadomian belt of western Europe. Three rock units forming the basement imply development of an
Andean-type active continental margin during the pre-Early Ordovician period. High-grade metamorphics (the Sünnice Group),
granitoids (the Bolu Granitoid Complex) and evolved felsic meta-volcanic rocks (the Çaşurtepe Formation) are exposed unconformably
beneath the Lower Ordovician fluvial clastics, between the Bolu-Yedigöller area, to the north of Bolu. The Bolu Granitoid
Complex comprises a group of intrusive rocks of variable composition and size, generated through multiple episodes of magmatism,
and is represented by two separate intrusive bodies within the study area, the Tüllükiriş Pluton in the west and the Kapıkaya
Pluton in the east. Both plutons are mainly tonalite and granodiorite in composition. More felsic and mafic compositional
varieties also occur. Major and trace element chemical characteristics of the granitoids, as well as biotite chemistry, indicate
that these are volcanic arc-type granitoids and are products of an immature arc developed during early stages of a subduction.
Furthermore, textural and chemical characteristics of the plutons show that these are subvolcanic intrusions, emplaced at
shallow depths, and are calc-alkaline in composition. The granitoidic plutons intrude the Çaşurtepe Formation. The Çaşurtepe
Formation is represented by arc-type volcanics and volcaniclastics. Both the Çaşurtepe Formation and the granitoids represent
subduction-zone magmatism constructed on a continental crust, represented by the Sünnice Group. The history is very similar
to Cadomian active margins as exposed in western Europe (i.e., the North Armorican and Bohemia massifs) and therefore the
basement to the Paleozoic of the West Pontides is considered to be a preserved remnant of the Cadomian belt.
We discuss nine palinspastic geological maps (Plates 1–9), at scale, which depict the evolution of the Tethys belt from the Pliensbachian (190 Ma) to the Tortonian (10 Ma). A Present structural map (Plate 10) is shown for comparison at the same scale with the same conventions. Our reconstructions are based on a kinematic synthesis (Savostin et al., 1986), a paleomagnetic synthesis (Westphal et al., 1986) and geological compilations and analyses concerning in particular the western domain (Ricou et al., 1986), the eastern passive margins (Kazmin et al., 1986a), the eastern active margins (Kazmin et al., 1986b), the Black Sea-Caspian Sea basins (Zonenshain and Le Pichon, 1986) and the ophiolites (Knipper et al., 1986).
The Trans-European Suture Zone (TESZ) comprises a series of sutures that developed by Palaeozoic amalgamation of the Phanerozoic Central Europe onto the Proterozoic Baltica and East European Plate during the formation of Pangea. Within TESZ, the Permian Basin in Poland forms the easternmost part of the Permian Central European Basin, which is bordered on the east by the East European Craton (EEC) and on the southwest by the Bohemian Massif. The axis of the basin, the Mid-Polish Trough, parallels the edge of the EEC. The Teisseyre–Tornquist Zone (TTZ) is a geological inversion zone in the Polish Trough. A large seismic experiment, the POLONAISE'97 project, was conducted in Poland during May of 1997 and targeted the deep structure of the TESZ and the complex series of upper crustal features associated with it. It included contributions from the geophysical communities in Poland, Denmark, the USA, Lithuania, Germany, Finland, Sweden and Canada. This large lithospheric seismic experiment deployed 613 instruments to record 64 shots along five profiles with a total length of about 2000 km. Moreover, five multichannel seismic reflection stations (90 and 120 channels) recorded all signals from shots. Two dimensional velocity models were derived by P-wave tomographic inversion. These models provide an initial interpretation of this massive data set and allow us to present a few significant seismic and tectonic observations. One of the most important is a very distinct asymmetry between the maximum thickness of the sedimentary cover in the Polish Trough (16–20 km) and the crustal root (∼50 km) associated with TESZ/TTZ.
We review extensively the evidence and arguments bearing on the nature of Palaeotethys in relation to the age of formation, location and multiplicity of Neotethyan strands and their fate. We conclude that Palaeotethys did not die early but was only finally subducted northwards in the Tertiary along the Vardar-Intra Pontide-East Anatolian suture. Neotethyan strands must have opened into it at all times. The Adriatic promontory remained attached to Africa but rotated anti-clockwise in the mid-Tertiary. The Pontides are considered to be Eurasian and the Cimmerides are viewed as a ‘collage terrain’ formed along an oblique-convergence margin. The south Aegean, Greek and Turkish microcontinental blocks were rifted-off Gondwana in the Triassic but formation of braided Neotethyan oceanic crustal strands was essentially confined to mid-Jurassic in the Hellenides and to the Cretaceous in Turkey.
We propose a new model of ophiolite genesis by asymmetrical spreading-ridge collapse in an attempt to explain both arc-like ophiolite chemistry prior to major volcanic arc edifice construction, and the synchroneity of sub-ophiolite metamorphic sole formation with Atlantic opening phases.
Jurassic dispersal of Hellenide blocks had little effect in the unexpanded Turkish mosaic, but northwards Cretaceous opening of Tauride Neotethyan strands caused oblique collision deformation in the Pelagonian zone and unresolvable complexity in the Aegean. Late Cretaceous and Tertiary arc-volcanism was related in part to continuing Palaeotethyan subduction, and in part to Neotethyan destruction initiated after ridge-collapse. Diachronous collisions ensued from the Late Cretaceous onwards but significant oceanic tracts must have persisted at least to Mid-Tertiary to satisfy Africa-Eurasia separation constraints determined from Atlantic anomaly fitting. Our favoured plate evolutionary model is presented in 7 sketch-maps.
Lower Palaeozoic rocks in the Karadere-Zirze area, east of Safranbolu (Pontides, northern Turkey), range from Early Ordovician to Silurian. Overlying the probably Tremadoc Bakacak Formation are Aydos Formation quartzites, followed conformably by the Karadere Formation, dated as Early Arenig to Early Llanvirn by means of graptolites which are assigned to seventeen genera and include three new forms: Eoglyptograptusbouceki, Prolasiograptushapluspraecursor and Undulograptus? mui. Late Arenig trilobites from the Karadere Formation include Bergamia, Cyclopyge, Dionidella?, Leioshumardia and Seleneceme. In the Limestone Member of the overlying Ketencikdere Formation, uncommon trilobites suggest only a mid- to late Ordovician age, but conodonts with Colour Alteration Index 5–6 indicate the Amorphognathustvaerensis Biozone (early Caradoc). Macrofossils are rare in the Siltstone Member, but conodonts from the middle of the unit suggest the highest subzone of the A.tvaerensis Biozone; the youngest visible strata are, on acritarch evidence, at least as high as Caradoc, but the Ashgill is not confirmed and the contact with overlying Silurian rocks is unexposed. The Findikli Formation comprises: a Lower Member, black argillites with Llandovery graptolites and acritarchs; and an Upper Member, grey shales with late Wenlock graptolites, overlain unconformably by Devonian rocks. The succession differs significantly from contemporaneous deposits in southern Turkey and its affinities lie with western Europe, including the Welsh Basin.
Recent models for the post-750 Ma Rodinian supercontinent dispersal (e.g. Hoffman, 1991) envision that cratons margined by Grenvillian belts, were reorganized before ca 540 Ma to form the Gondwanan supercontinent. Laurentia and Baltica distanced themselves from Gondwana by moving out of the Rodinian cratonal cluster. West Gondwana, of which Avalon was a part during the late Proterozoic to Cambrian cratonal assembly, consisted mainly of Africa and South America.The main geological evidence is presented for: (1) a transition from continental platform conditions to those of a subduction-related volcanic arc regime in Late Proterozoic time during the dispersal of the Rodinian supercontinent, and the resulting assembly of the Gondwanan supercontinent; and (2) a second transition that marked a reversal from the volcanic arc regime to marine platformal environments by early Cambrian time.Evidence for progressive instability of the continental shelf margining the Rodinian supercontinent is contained in late Proterozoic olistostromes, mylonite zones, calc-alkaline magmatism, and arc-derived clastic rocks, some being glacigenic, during three phases of the Avalonian orogeny.By early Cambrian time the reversal from a tectonically unstable volcanic arc regime to more stable platformal conditions took place as Avalon, Armorica and related microcontinental blocks rifted from Gondwana. These Gondwanan fragments sequentially come into collision, first with each other and Baltica, and then with Laurentia in Mid to Late Paleozoic time as Pangaea was being assembled.
Suturing of the supercontinent Rodinia in the Grenville event (~ 1000 Ma) was followed by rifting in the late Proterozoic (~ 800-700 Ma), reorganization to Gondwana in the Pan-African (~ 700-500 Ma) and further accretion to develop Pangea at the end of the Paleozoic. One of the Rodinian rifts followed part of the Grenville suture, it produced the margin of eastern North America and southern Baltica and the contrasting margin of west Gondwana in present South America. The Paleozoic accretionary wedge against the Grenville-age margin of North America and Baltica contains Avalonian/Cadomian terranes that exhibit Pan-African erogenic events ± sediments apparently developed while the terranes were in or near Gondwana. These terranes carry lower-Paleozoic fauna (Acado-Baltic) that are not indigenous to North America and Baltica.UPb zircon ages range from 1500-1000 Ma in Grenville terranes and from 800–500 Ma with minor inheritance in Avalonian terranes; they are generally much older in Cadomian terranes, implying very little resetting during Pan-African events. TDM ages are generally 2000–1200 Ma in Grenville terranes, 1300–600 Ma in Avalonian terranes and 2000–1200 in Cadomian terranes. These summary data show that: (1) the Grenville orogenic event produced almost no juvenile crust; (2) the Avalonian terranes of North America contain crust that evolved primarily in the late Proterozoic, possibly as a mixture of juvenile Pan-African material and Grenville or slightly older material; (3) the Cadomian terranes of Europe consist of old (middle-Proterozoic to Archean) crust with minor juvenile Pan-African material. The Avalonian terranes apparently evolved near, and partly on, the Grenville-age crust now in South America during the intense orogeny associated with rotation of Gondwana away from North America. The Cadomian terranes of Europe, however, appear to be fragments of other parts of Gondwana, probably West Africa.
Although almost universally ignored, the effect of errors in the uranium decay-constants on U–Pb concordia-intercept ages (and Pb–Pb ages) are significant, and not equivalent to those of simple U–Pb ages. Equations are derived for concordia-intercept age-errors that take decay-constant errors into account.
The Cadomian basement and the Cambro-Ordovician overstep sequence in Saxo-Thuringia is characterized by clastic sedimentation from the Late Neoproterozoic to the Ordovician. Magmatism in the Avalonian–Cadomian Arc preserved in Saxo-Thuringia occurred between ca. 570 and 540 Ma. Peri-Gondwanan basin remnants with Cadomian to Early Palaeozoic rocks are exposed as very low-grade metamorphosed rocks in six areas (Schwarzburg Anticline, Berga Anticline, Doberlug Syncline, North Saxon Anticline, Lausitz Anticline, and Elbe Zone). A hiatus in sedimentation between 540 and 530 Ma (Cadomian unconformity) is related to the Cadomian Orogeny. A second gap in sedimentation occurred during the Upper Cambrian (500 to 490 Ma) and is documented by a disconformity between Lower to Middle Cambrian rocks and overlying Tremadocian sediments. Major and trace-element signatures of the Cadomian sediments reflect an active margin (“continental arc”), those of the Ordovician sediments a passive margin. The Cambrian sediments have inherited the arc signature through the input of relatively unaltered Cadomian detritus. Initial Nd and Pb isotope data from the six Saxo-Thuringian areas demonstrate that there is no change in source area with time for each location, but that there are minor contrasts among the locations. (1) Cadomian sediments from the Lausitz Anticline, the Doberlug Syncline and the Elbe Zone have lower 207Pb/204Pb than all other areas. (2) The core of the Schwarzburg Anticline, which is overprinted by greenschist facies conditions and detached, is isotopically heterogeneous. One part of its metasedimentary units has less radiogenic Nd than sediments from other low-grade units of similar age in the same area. (3) Cadomian sediments from the Schwarzburg Anticline show an input of younger felsic crust. (4) The Rothstein Group shows distinct input of young volcanic material. Also, (5) Cadomian sediments from the Lausitz Anticline, the Elbe Zone and parts of the North Saxon Anticline are characterized by input from an old mafic crust. Nd isotope data of the remaining areas yield average crustal residence ages of the sediment source of 1.5–1.9 Ga, which suggests derivation from an old craton as found for other parts of the Iberian–Armorican Terrane Collage. Similarly, the Pb isotope data of all areas indicate sediment provenance from an old craton.The rapid change of lithologies from greywacke to quartzite from the Late Neoproterozoic (Cadomian basement) to the Ordovician does not reflect changes in sediment provenance, but is essentially due to increased reworking of older sediments and old weathering crusts that formed during various hiatus of sedimentation. This change in sediment maturity takes its chemical expression in lower overall trace-element contents in the quartzite (dilution effect by quartz) and relative enrichment of some trace-elements (Zr, MREE, HREE due to detrital zircon and garnet). The Rb–Sr systematics of the quartzites and one Ordovician tuffite was disturbed (most likely during the Variscan Orogeny), which suggests a lithology-controlled mobility of alkali and calc-alkali elements. By comparison with available data, it seems unlikely that only Nd TDM model ages are useful to distinguish between West African and Amazonian provenance. Nd TDM model ages of 1.5 to 1.9 Ga in combination with paleobiogeographic aspects, age data from detrital zircon, and palaeogeographic constraints, especially through tillites of the Saharan glaciation in the Hirnantian, strongly indicate a provenance of Saxo-Thuringia from the West African Craton.
The end of the Proterozoic–beginning of the Cambrian is marked by some of the most dramatic events in the history of Earth. The fall of the Ediacaran biota, followed by the Cambrian Explosion of skeletonised bilaterians, a pronounced shift in oceanic and atmospheric chemistry and rapid climatic change from ‘snowball earth’ to ‘greenhouse’ conditions all happened within a rather geologically short period of time. These events took place against a background of the rearrangement of the prevailing supercontinent; some authors view this as a sequence of individual supercontinents such as Mesoproterozoic Midgardia, Neoproterozoic Rodinia and Early Cambrian Pannotia. Assembled in the Mesoproterozoic, this supercontinent appears to have existed through the Neoproterozoic into the Early Cambrian with periodic changes in configuration. The final rearrangement took place during the Precambrian–Cambrian transition with the Cadomian and related phases of the Pan-African orogeny. The distribution of Early Cambrian molluscs and other small shelly fossils (SSF) across all continents indicates a close geographic proximity of all major cratonic basins that is consistent with the continued existence of the supercontinent at that time. Subsequently, Rodinia experienced breakup that led to the amalgamation of Gondwana, separation of Laurentia, Baltica, Siberia and some small terranes and the emergence of oceanic basins between them. Spreading oceanic basins caused a gradual geographic isolation of the faunal assemblages that were united during the Vendian–Early Cambrian.
The Tornquist and Iapetus Suture Zones result from amalgamation of three
plates (Laurentia, Baltica and Eastern Avalonia) during the Early
Paleozoic Caledonian orogeny (similar to 440 Ma). We present a
comparison of the velocity structure of the contrasting Proterozoic and
Paleozoic lithosphere across the margins of Eastern Avalonia based on
two deep seismic experiments, MONA LISA and VARNET in the SE North Sea
and SW Ireland, respectively, Both velocity models show three different
crustal types: (a) a high-velocity, three-layered shield type
Proterozoic crust (in Baltica and Laurentia) to the north; (b) a
transitional crust in the central part across the suture zones; and (c)
Eastern Avalonian crust to the south. However, the sub-Moho velocities
are similar to 7.8 km/s under the similar to 34-km-thick Baltica crust
and similar to 8.2 km/s under the 26-km-thick Eastern Avalonian crust on
the MONA LISA-I profile, in contrast to similar to 7.8 km/s under the
similar to 31-km-thick Eastern Avalonian crust and similar to 8.1 km/s
under the similar to 33 km thick Laurentian crust on the VARNET profile.
These differences in the sub-Moho velocity structure are interpreted to
be related to a change in subduction polarity between the Tornquist Sea
and the Iapetus Ocean or in the direction of shearing in the mantle
during collision tectonics, (C) 1999 Elsevier Science B.V. All rights
reserved.
Very different palaeogeographical reconstructions have been produced by a combination of palaeomagnetic and faunal data, which are re-evaluated on a global basis for the period from 500 to 400 Ma, and are presented with appropriate confidence (or lack of it) on six maps at 20 Ma intervals. The palaeomagnetic results are the most reliable for establishing the changing palaeolatitudes of Baltica, Laurentia and Siberia. However, global palaeomagnetic reliability dwindles over the 100 Ma, and more evidence for relative continental positioning can be gleaned from study of the distribution of the faunas in the later parts of the interval. The new maps were generated initially from palaeomagnetic data when available, but sometimes modified, and terranes were positioned in longitude to take account of key faunal data derived from the occurrences of selected trilobites, brachiopods and fish. Kinematic continuity over the long period is maintained. The many terranes without reliable palaeomagnetic data are placed according to the affinities of their contained fauna. The changing positions of the vast palaeocontinent of Gondwana (which has hitherto been poorly constrained) as it drifted over the South Pole during the interval have been revised and are now more confidently shown following analysis of both faunal and palaeomagnetic data in combination, as well as by the glacial and periglacial sediments in the latest Ordovician. In contrast, the peri-Gondwanan and other terranes of the Middle and Far East, Central Asia and Central America are poorly constrained.
The scope of this study is to understand better the pre-Early Ordovician history of the west
Pontides of northern Turkey by focusing on the best-exposed part of the Bolu Massif, which is located
between Bolu and Yedigöller (Seven Lakes). The Palaeozoic rocks of the west Pontides tectonic belt of
northern Turkey comprise a transgressive sedimentary sequence known as ‘Palaeozoic of Istanbul.’ In
a few areas, the basement of the Palaeozoic sequence is exposed, the largest part of which is the Bolu
Massif, which is located in the middle of the west Pontides. The lowermost unit of the Palaeozoic of
Istanbul in the Bolu area is the Isigandere Formation, which is made up of fluvial red conglomerates
and sandstones of Lower Ordovician age. Three different units are exposed unconformably beneath
these continental clastics, forming the Bolu Massif. From the structural base to the top, these are as
follows: (1) a high-grade metamorphic unit, known as the Sünnice Group); (2) granitoid intrusions,
known as the Bolu Granitoid Complex; and (3) a greenschist meta-volcanic sequence (the Çasurtepe
Formation).
Remnants of two ‘Palaeotethyan’ oceanic basins are exposed in the Central Pontides of northern Turkey, separated by a continental sliver and an oceanic arc. The southern basin corresponds to the main Tethys (‘Palaeotethys’), which partially closed in Early Mesozoic time following northward subduction under the southern, active continental margin of Eurasia.
The northern basin (Küre Complex) opened above the ‘Palaeotethyan’ subduction zone as a marginal basin, following rifting of a continental fragment (Istanbul fragment) from Eurasia. Marginal basin opening apparently dates from the Late Palaeozoic in the east (Küre basin) and from the Triassic in the west (Kocaeli basin). Basin closure was achieved by southward subduction-accretion, in pre-Late Jurassic times, leaving ‘Neotethys’ open to the south.
Counterparts of the Küre Complex are found in the adjacent Crimea (Taurian Series), Istranca (Zabernevo Complex), Dobrogea (Nalbant flysch) and Caucasus (pre-Late Jurassic Southern Slope Basin) regions. Basin opening was accompanied by oceanic crust genesis, at least in the Pontides and Caucasus. Closure before Mid-Jurassic time was achieved by subduction-accretion processes, whereby oceanic crust and deep-sea sediments (including sulphides) were detached and structurally assembled, while oceanic basement was subducted. Marginal basin opening and closure is seen as one in a series of events along a long-lived, active south Eurasian continental margin.
The Armutlu Peninsula and adjacent areas in NW Turkey play a critical role in tectonic reconstructions of the southern margin of Eurasia in NW Turkey. This region includes an inferred Intra-Pontide oceanic basin that rifted from Eurasia in Early Mesozoic time and closed by Late Cretaceous time. The Armutlu Peninsula is divisible into two metamorphic units. The first, the Armutlu Metamorphics, comprises a ?Precambrian high-grade metamorphic basement, unconformably overlain by a ?Palaeozoic low-grade, mixed siliciclastic/carbonate/volcanogenic succession, including bimodal volcanics of inferred extensional origin, with a possibly inherited subduction signature. The second unit, the low-grade İznik Metamorphics, is interpreted as a Triassic rift infilled with terrigenous, calcareous and volcanogenic lithologies, including basalts of within-plate type. The Triassic rift was unconformably overlain by a subsiding Jurassic–Late Cretaceous (Cenomanian) passive margin including siliciclastic/carbonate turbidites, radiolarian cherts and manganese deposits. The margin later collapsed to form a flexural foredeep associated with the emplacement of ophiolitic rocks in Turonian time. Geochemical evidence from meta-basalt blocks within ophiolite-derived melange suggests a supra-subduction zone origin for the ophiolite. The above major tectonic units of the Armutlu Peninsula were sealed by a Maastrichtian unconformity. Comparative evidence comes from the separate Almacık Flake further east.Considering alternatives, it is concluded that a Mesozoic Intra-Pontide oceanic basin separated Eurasia from a Sakarya microcontinent, with a wider Northern Neotethys to the south. Lateral displacement of exotic terranes along the south-Eurasian continental margin probably also played a role, e.g. during Late Cretaceous suturing, in addition to overthrusting.
Earlier geological work in the Istanbul zone, western Pontide tectonic belt, has revealed the presence of extensive basement outcrops exposed underneath Palaeozoic and Mesozoic to Tertiary cover sequences. The basement of suspected Neoproterozoic age plays an important role in understanding the crustal accretion process in NW Turkey. We report the first results of a detailed Pb-Pb and U-Pb zircon study complemented by Nd-Sr whole rock and mineral data from basement rocks exposed in the Karadere valley, Safranbolu area. Five samples were selected for this study, comprising three metagranitoids and two metasediments. Zircon geochronology indicates that the metagranitoids were formed during Late Proterozoic pan-African magmatic events between 590 and 560 Ma. The rocks are of tonalitic and granitic composition and have low Nb/Y ratios and Ti contents, consistent with those of arc rocks. A continental arc setting is supported by their Sr and Nd isotope data that indicate a contribution of a mantle source as well as crustal assimilation during magma genesis. The metasediments can clearly be distinguished from the metagranitoids by their higher 87Sr/86Sr ratios and lower )Nd-values at 580 Ma, which supports the suggestion that the arc was underlain by mature continental crust. Zircons from the metasediments yield a range of Pb-Pb ages between 1,860 and 710 Ma. Thirty per cent of them fall between 890 and 710 Ma, possibly suggesting a derivation from Gondwana (Afro-Arabian) regions. A Sm-Nd garnet-whole rock analysis obtained on a metagranite gives an age of 559NJ Ma, which either reflects pre-metamorphic magmatic growth of garnet in a felsic melt or a syntectonic high-temperature metamorphic event. Uplift and cooling of the basement is further constrained by Rb-Sr biotite ages of 548-545 Ma. These lower Cambrian mineral ages demonstrate that the Istanbul zone was not thermally reactivated during the Hercynian, Cimmerian or Alpine orogeny, in contrast to its neighbouring tectonic zones, confirming its role as a suspect terrane in the modern western Pontide tectonic belt.
Gondwana and the associated peri-Gondwana fragments cover an area which is about two-thirds of the area of all continents above the 2000 m bathymetric contour. The Gondwana continents formed by break-up during a geologically short period (Jurassic to Tertiary times), coinciding with the eruption of flood basalts. The uplift caused by associated plumes probably provided the extra stresses necessary for continental separation. It is unclear whether plumes alone were able to fragment Gondwana. By contrast, the smaller, more numerous, peri-Gondwana fragments are generally elongate and their period of formation spans the whole of the Phanerozoic. Their shapes are tentatively attributed to trench suction and associated effects caused by south dipping slabs acting mostly on the northern margin of Gondwana; their migration to retreat of the hinge lines of the subduction zones generally northwards. Gondwana's position during the Cambrian to Triassic interval is uncertain. The most recent apparent polar wander paths (APWPs), based on high quality palaeomagnetic data, are incompatible with the distributions of corals, tillites and the Clarkeia shelly fauna of Silurian age. Somewhat surprisingly, a new APWP based on all available palaeomagnetic poles is in much better agreement with the fossil and sediment distributions even though many poles have not been magnetically tested. A solution to the 'Pangaea problem' is proposed, in which it is suggested that many of the Gondwana poles for the period 340-200 Ma have been remagnetised. However, all the APWPs give improbable polar positions for some Early Cambrian Moroccan archaeocyathids. Rates of change of pole position for the new modified APWP ('apparent drift rates') are similar to post-Triassic rates, implying that plate driving forces have not changed much during the Phanerozoic.
Within the European Variscan belt, the Armorican Massif (northwestern France) contains an isolated fragment of the North Atlantic Panafrican belt — the Cadomian block. Mostly unaffected by Variscan deformation, this block is composed of Neoproterozoic rocks, ranging in age from 620 to 540 Ma (Brioverian), locally overlying a composite basement of Icartian (2000 Ma) or Pentevrian (750 Ma) age.The Cadomian tectonics, the last magmatic manifestations of which are dated at around 540 Ma, were sealed by a cover of Early Cambrian rocks in Normandy and Early Ordovician rocks in Brittany.Five units are distinguished in this Cadomian block — Trégor, Saint-Brieuc, Guingamp, Saint-Malo and Fougères. Although the units are bound by major faults, the overall coherence of their different protolithic characteristics suggests that they can be fitted into a simple geodynamic model.The Trégor Unit, represented by the North Trégor Batholith of crustal affinity and its Icartian host rock, probably reflects an early Cadomian evolution.The Saint-Brieuc Unit, essentially made up of magmatic rocks of juvenile affinity, includes two assemblages juxtaposed by the Cadomian tectonics: (1) a volcanosedimentary succession formed in a typical island-arc setting reflecting subduction around 610 Ma; and (2) a volcanic–plutonic complex emplaced around 590 Ma, in an extensional active continental margin of Pentevrian age.The Guingamp Unit, predominantly migmatitic, includes a tectonic slice of deep origin, the extrusion of which accompanied the exhumation of the migmatites; it may represent the trace of a possible suture.The Saint-Malo Unit is composed of Brioverian detrital rocks, the significance of which is uncertain — passive continental margin or accretionary prism; it is structured around a late migmatitic dome (540 Ma).The Fougères Unit corresponds to the outer domain of the Cadomian orogeny; it was only weakly deformed by Cadomian tectonics, and is intruded by the large Mancellian Batholith of crustal origin, dated at 540 Ma.Together the structural units are interpreted in the framework of an evolving active margin juxtaposing continental margin, marginal basin and volcanic arc, before being shortened during the Cadomian convergent tectonics.
Late Neoproterozoic to early Paleozoic, Cadomian tectonic elements are widespread in the southeastern Alpine–Mediterranean mountain belts, with discontinuous exposure extending from the Alps to the Menderes Massif in Turkey. The sequences include voluminous plutonic island and continental arc successions, some ophiolites of variable, late Neoproterozoic and Cambrian to early Ordovician ages, high- to medium-grade metamorphic sequences and subordinate metasediments. Geological and geochronological data suggest that these Cadomian elements partly experienced tectonothermal activity including metamorphism and magmatism between ca. 650 and 600 Ma, followed by further I- and S-type plutonism in an Andean-type continental margin setting ca. between 570 and 520 Ma. Subsequently, a major rift zone developed which resulted in continental stretching and subsequent formation of a back arc basin which is dated as late Cambrian. Rifting is followed by oceanic spreading which commenced ca. at the Cambrian/Ordovician boundary, possibly in a back-arc setting. This tectonic scenario suggests that Alpine–Mediterranean Cadomian tectonic elements were accreted to Gondwana during early Cadomian events (ca. 600–650 Ma). Subsequently, they were likely part of a long-lasting ‘outer’ subduction zone of Gondwana at the margin of a Panthalassa-type ocean during late Neoproterozoic III and Cambrian. Due to back-arc spreading, continental pieces started to split off from Gondwana ca. at the Cambrian–Ordovician boundary.
The most profound biotic crisis in the Earth’s history, causing the near extinction of both terrestrial and marine life, occurred at the end of the Permian period about 253 Myr ago and marks the Paleozoic–Mesozoic era boundary. The cause of this event is still a matter of vigorous debate, with both brief and catastrophic as well as gradual mechanisms having been proposed. Similar to a recent landmark study, this study uses the U–Pb method on zircons from the uppermost Permian/lowermost Triassic ash fall deposits at Meishan (Zhejiang Province, SE China) in order to examine time and rate constraints for these events. The results of both this study and previous work show that for these ash layers, the effects of Pb loss are combined with varying amounts and sources of inheritance, resulting in an age scatter which prohibits the extraction of a statistically robust age in many cases. Though the effects of Pb loss on the zircons analyzed in this study were reduced by leaching the grains in hydrofluoric acid (as opposed to commonly applied air abrasion) prior to analysis, the presence within a single ash layer of multiple generations of older xenocrysts (in many cases only slightly older than the depositional age) has made quantitative interpretation even more difficult. When these combined phenomena bias individual zircon ages by less than a percent, they are extremely difficult to deconvolute, and, if multi-grain analyses are used, can become impossible to recognize (because of the resulting age averaging). Monte Carlo simulations using actual measurements of individual zircon crystals show that age excursions due to Pb loss and xenocrystic contamination for the Meishan bentonites are easily homogenized to the point of undetectability when replicate analyses of multi-grain zircon samples are compared. Thus this study uses only high-precision analyses of single crystals, whether from our work or that of previous studies. Three main conclusions have emerged. First, our data require a significant increase in the age of the Permian–Triassic boundary by more than 2 myr compared to the previous study, which shifts the age to a value older than 253 Ma. Second, neither our data nor those from previous work can confirm or negate the possibility of a very abrupt biotic crisis. Third, even large suites of very high-quality, single-zircon U–Pb analyses for these tuffs cannot, in most cases, yield objective, reliable, and robust dates with accuracies at the sub-myr level – though the temptation to perform arbitrary selection of subsets of the analyses for that purpose is almost irresistible. The last conclusion is not an indictment of zircon U/Pb dating in general (other rocks and other zircon populations can – and do – behave very differently), and further technical advances will likely improve our ability to prepare grains or sub-grains of adequately enhanced quality for analysis. Consequently, the results of the present study strongly suggest that for problems requiring time-scale accuracy, inferences from zircon U–Pb dating must be based on sufficiently large suites of single-crystal or crystal domain, high-precision analyses (<1% error) that are realistically interpreted.
The Teisseyre–Tornquist transcurrent fault zone forms the southwestern margin of Baltica in central Europe. Across this fault zone Baltica is fringed by several tectonostratigraphic terranes, some with Cadomian basement. Five tectonostratigraphic terranes defined by dissimilar Cadomian basement and Paleozoic cover units are present in the Czech Republic and southern Poland between the Bohemian Massif and the Teisseyre–Tornquist fault zone. Two of these terranes, the Małopolska terrane and the Lubliniec–Zawiercie–Wieluń terrane, lodged in a restraining bend of the Teisseyre–Tornquist transcurrent fault zone during the sinistral transpression of Eastern Avalonia and Baltica, and were deformed during the Caledonian orogeny. The Łysogóry terrane, situated in a releasing bend of the Teisseyre–Tornquist transcurrent fault zone, has a thicker Paleozoic sedimentary succession than the neighboring terranes, and was deformed during the Variscan orogeny. The Moravian terrane is part of the Rhenohercynian zone of Armorica–Cadomia. The Upper Silesia terrane acted as an indentor and impinged on the assemblage of East Avalonian and Armorican–Cadomian terranes during the Early Carboniferous and deformed the polyorogenic Kraków mobile belt and the Moravian mobile belt. The Kraków mobile belt, deformed in both the Caledonian and Variscan orogenies, includes the western margin of the Małopolska terrane and the Lubliniec–Zawiercie–Wieluń terrane. It is also the locus of Early Carboniferous age magmatism with porphyry copper mineralization.
Because the Hercynian overprint was extremely weak, the Sierra de Córdoba (southeastern Ossa-Morena Zone, OMZ) provides an excellent opportunity to study the tectonic evolution of sequences deposited close to the Late Neoproterozoic–Early Palaeozoic boundary. In order to put constraints on the sources and geodynamic significance of the Late Proterozoic magmatism, a representative set of 18 igneous rocks, and 3 interbedded sedimentary rocks from the San Jerónimo Formation have been studied for major and trace element geochemistry and for the Sm–Nd isotopic systematics. The igneous rocks are generally porphyritic to microporphyritic andesites, with abundant plagioclase (±amphibole) phenocrysts. With the exception of two intrusive rocks, possibly not related to the Late Proterozoic episode, all the samples display positive εNd550 Ma values, ranging from +2.9 to +7.6. Most of them, with +4<εNd550 Ma<+6, exhibit LREE enrichment, high La/Nb ratios, and elevated Zr/Nb ratios ranging from 21 to 32. There is no obvious correlation between the shape of REE patterns, La/Nb ratios and εNd550 Ma values, precluding simple models of late-stage interaction with typical crustal components having low εNd and high LREE/HREE and La/Nb ratios. Based on their major element composition and enriched, continental crust-like trace element characteristics, combined with distinctly positive εNd initial values, the Córdoba andesites document an episode of crustal growth through the addition of calc-alkaline magmas, extracted from a mantle reservoir which was strongly depleted in LREE on a time-integrated basis. The occurrence of interlayered sediments of continental provenance (negative εNd values) does not favour a purely ensimatic arc setting, remote from continental land masses, for this subduction-related magmatism, but the geochemical data suggest an active margin environment located on relatively juvenile crust. In any case, the Córdoba andesites document the addition of materials chemically similar to the bulk continental crust which were extracted from mantle sources with strong time-integrated LREE depletion. Therefore, they provide evidence for crustal growth related to Cadomian orogenic events during Late Proterozoic times.
Ductile deformation and polyphase metamorphism in the Ossa-Morena zone of the Iberian massif are related to two major tectonothermal episodes of Cadomian (late Neoproterozoic to early Cambrian) and Variscan age (middle to late Paleozoic). The available petrological, structural and geochronological data suggest that a number of tectono-metamorphic and magmatic episodes occurred during the 620–480 Ma interval that would comprise a complete Cadomian Wilson cycle. The geodynamic scenario was that of an Andean-type continental margin. An evolutionary model is presented for this orogeny comprising stages of volcanic arc generation, crustal thickening, back-arc extension, tectonic inversion and cratonization. A correlation with comparable areas from pre-Mesozoic massifs elsewhere in Europe is proposed, in particular with the Armorican massif of northern France.
During the Neoproterozoic, a supercontinent commonly referred to as Rodinia, supposedly formed at ca. 1100 Ma and broke apart at around 800–700 Ma. However, continental fits (e.g., Laurentia vs. Australia–Antarctica, Greater India vs. Australia–Antarctica, Amazonian craton [AC] vs. Laurentia, etc.) and the timing of break-up as postulated in a number of influential papers in the early–mid-1990s are at odds with palaeomagnetic data. The new data necessitate an entirely different fit of East Gondwana elements and western Gondwana and call into question the validity of SWEAT, AUSWUS models and other variants. At the same time, the geologic record indicates that Neoproterozoic and early Paleozoic rift margins surrounded Laurentia, while similar-aged collisional belts dissected Gondwana. Collectively, these geologic observations indicate the breakup of one supercontinent followed rapidly by the assembly of another smaller supercontinent (Gondwana). At issue, and what we outline in this paper, is the difficulty in determining the exact geometry of the earlier supercontinent. We discuss the various models that have been proposed and highlight key areas of contention. These include the relationships between the various ‘external’ Rodinian cratons to Laurentia (e.g., Baltica, Siberia and Amazonia), the notion of true polar wander (TPW), the lack of reliable paleomagnetic data and the enigmatic interpretations of the geologic data. Thus, we acknowledge the existence of a Rodinia supercontinent, but we can place only loose constraints on its exact disposition at any point in time.
New U–Pb zircon and titanite dates from syn-tectonic plutons on the British Channel Island of Sark constrain the time span of plutonism, fabric development, and cooling in this part of the Neoproterozoic Cadomian magmatic arc. The Tintageu leucogneiss is a mylonitic unit that was dated previously at 615.6+4.2−2.3 Ma. The Port du Moulin quartz diorite, which intruded the Tintageu unit, contains a high-strain solid-state deformation fabric that is less intense than, but parallel to, fabrics in the leucogneiss and yields a U–Pb zircon date of 613.5+2.3−1.5 Ma. The Little Sark quartz diorite also displays solid-state deformation fabrics in addition to relict magmatic textures, and yields a U–Pb zircon date of 611.4+2.1−1.3 Ma. The North Sark granodiorite is largely penetratively undeformed, exhibits mainly magmatic fabrics and textures and has a U–Pb zircon date of 608.7+1.1−1.0 Ma. Two fractions of titanite from each intrusion are essentially concordant and are identical within error, with mean dates of 606.5±0.4 Ma (Port du Moulin quartz diorite), 606.2±0.6 Ma (Little Sark quartz diorite), 606.4±0.6 Ma (North Sark granodiorite). The new U–Pb data, in combination with previous U–Pb and 40Ar/39Ar data and previous field studies, confirm the syn-tectonic nature of the Sark plutons and quantify the time span (ca. 7 m.y.) required for intrusion and sufficient crystallization of each body to record incremental strain during waning deformation. Titanite U–Pb and hornblende 40Ar/39Ar dates mark final cooling about 2 m.y. after intrusion of the last pluton.
The Balkan-Carpathian ophiolite (BCO), which outcrops in Bulgaria,
Serbia and Romania, is a Late Precambrian (563 Ma) mafic/ultramafic
complex unique in that it has not been strongly deformed or
metamorphosed, as have most other basement sequences in Alpine Europe.
Samples collected for study from the Tcherni Vrah and Deli Jovan
segments of BCO include cumulate dunites, troctolites, wehrlites and
plagioclase wehrlites; olivine and amphibole-bearing gabbros;
anorthosites; diabases and microgabbros; and basalts representing
massive flows, dikes, and pillow lavas, as well as hyaloclastites and
umbers (preserved sedimentary cover). Relict Ol, Cpx and Hbl in cumulate
peridotites indicate original orthocumulate textures. Plagioclase in
troctolites and anorthosites range from An 60 to An
70. Cumulate gabbro textures range from ophitic to
poikilitic, with an inferred crystallization order of Ol-(Plag+Cpx)-Hbl.
The extrusive rocks exhibit poikilitic, ophitic and intersertal
textures, with Cpx and/or Plag (Oligoclase-Andesine) phenocrysts. The
major opaques are Ti-Magnetite and Ilmenite. The metamorphic paragenesis
in the mafic samples is Chl-Trem-Ep, whereas the ultramafic rocks show
variable degrees of serpentinization, with lizardite and antigorite as
dominant phases. Our samples are compositionally and geochemically
similar to modern oceanic crust. Major element, trace element and rare
earth element (REE) signatures in BCO basalts are comparable to those of
MORB. In terms of basalt and dike composition, the BCO is a 'high-Ti' or
'oceanic' ophiolite, based on the classification scheme of Serri [Earth
Planet. Sci. Lett. 52 (1981) 203]. Our petrologic and geochemical
results, combined with the tectonic position of the BCO massifs
(overlain by and in contact with Late Cambrian island arc and back-arc
sequences), suggest that the BCO may have formed in a mid-ocean ridge
setting. If the BCO records the existence of a Precambrian ocean basin,
then there may be a relationship between the BCO and the Pan-African
ophiolites from the Arabian-Nubian Shield. We suggest that the BCO is
the missing link between the Pan-African and the Avalonian-Cadomian
peripheral orogens of Murphy and Nance [Geology 19 (1995) 469].
Petrologic and geochronologic investigations in Gümüşhane and Rize areas
- E Çoğulu
C ¸ og ˘ ulu, E., 1975. Petrologic and geochro-nologic investigations in Gu ¨ mu ¨ s¸hane and Rize areas. Habilitation Thesis, _I.T.U¨. Library (in Turkish), no. 1034
Significant Pb loss of Cadomian zircons due to Alpine subduction of pre-Alpine basement of eastern Crete (Greece)
- S S Romano
- W Do¨
- G Zulauf
Romano, S.S., Do¨, W. and Zulauf, G., 2004. Significant Pb loss of Cadomian zircons due to Alpine subduction of pre-Alpine basement of eastern Crete (Greece). Int. J. Earth Sci., 93(5), 844–859.
Petrogenesis and Metalogenesis of Bolu-Yedigöller Granitoids
- P A M Ustaömer
Ustao¨, P.A.M., 1996. Petrogenesis and Metalogenesis of Bolu-Yedigoï Granitoids. Unpublished PhD Thesis (in Turkish), _ I.U ¨. Science Institute, 196 pp.
Comparative study of the plutons in northwest Anatolia Unpublished PhD thesis
- Bu¨
Bu¨. Comparative study of the plutons in northwest Anatolia. Unpublished PhD thesis (in Turkish), _ I.T.U ¨. Mining Faculty.
The Cadomian Orogeny
- Ley
ley, eds. The Cadomian Orogeny, Geol.
Tectonic Setting and Emplacement of the
- P A Mugan-Ustaomer
Comparative study of the plutons in northwest Anatolia
- Y Bürküt
An example for a Pre‐Ordovician Arc magmatism from northern Turkey: geochemical investigation of Çaşurtepe Formation (Bolu, W Pontides)
- Ustaömer P.A.