Article

Evolution of late Neoproterozoic to early Paleozoic tectonic elements in Central and Southeast European Alpine mountain belts: Review and synthesis

July 2002
Tectonophysics 352(1):87-103

July 2002
352(1):87-103

DOI:10.1016/S0040-1951(02)00190-7

Authors:

University of Salzburg

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.

Constraining the provenance and evolution of the Western Alps Molasse Basin by detrital zircon U–Pb geochronology

Article

Full-text available

Apr 2021

Molasse basin is one of the best-preserved pieces of evidence of the Alpine orogeny. Molasse and flysch sequences deposited during the convergence between the Adriatic and the European continents recorded various geological processes. However, detailed provenance analysis of the foreland basin in the Western Alps is still in need of precise data for molasse strata. This paper provides new detrital zircon U–Pb geochronology results from five sandstone samples to constrain the provenance of the Molasse Basin in the Western Alps. The main populations in zircon age spectra correspond to the four tectonothermal events defined in the Alpine domain: the late Neoproterozoic to early Cambrian magmatic event, the pre-Variscan rifting event, the Variscan orogeny, and the Permian extensional event, respectively. Two magmatic zircons (100 ± 2 Ma and 130 ± 5 Ma) and one metamorphic zircon grain (116 ± 3 Ma) yield Cretaceous age. The metamorphic one was probably originated in the Internal zone. A contribution of the Valaisan unit as part of the source terrane is possible to account for the Cretaceous magmatic zircons. Comparing our results with published detrital zircon age data using multidimensional scaling, we infer that the Austroalpine unit was an essential provenance of the Western Alps Molasse Basin during the late Oligocene and the middle Miocene. During the middle Miocene, the deposition of the Molasse Basin was strongly influenced by the exhumation of the External Massifs and the propagation of the subalpine fold-and-thrust belt. Meanwhile, the French Massif Central was also possible to provide a limited proportion of the material for the basin.

Cambrian-Ordovician continental magmatic arc at the northern margin of Gondwana: Insights from the Schladming Complex, Eastern Alps

Article

Feb 2021
LITHOS

The Austroalpine Unit is one of the major tectonic units in the Alps and contains distinct Pre-Mesozoic basement units, which underwent in part pre-Variscan (Ordovician), Variscan and Alpine events and preserved information of pre-Variscan magmatism and ocean slab relics. The Schladming Complex is an important part of the Austroalpine basement unit, its orthogneiss and paragneiss were intruded by a large number of the Cambrian to Ordovician magmatic rocks, which recorded the tectonic evolution related to the Proto-Tethys, but for which there have been very few studies carried out, especially in geochronology and geochemistry. In this study, for the first time we systematically investigated the magmatic rocks of the Schladming Complex by zircon UPb chronology, zircon LuHf isotopic and geochemical to understand the tectonic setting and evolution of the Austroalpine Unit during the Early Paleozoic. Our study shows that the granodioritic gneisses (539–538 Ma) and the fine-grained amphibolite (531 ± 2 Ma) represent a bimodal magmatism. Geochemically, the granodioritic gneisses belong to A2-type granite and originated from the lower crust, the fine-grained amphibolites have an E-MORB affinity and derived from the lithospheric mantle. This association further implies that the Schladming Complex formed in a back-arc rift tectonic setting in the Early Cambrian. A medium-grained amphibolite gives an age of 495 ± 5 Ma, exhibits ocean island basalt-like geochemical features and positive εHf(t) values (+5.3 ~ +10.9) indicating that the medium-grained amphibolite derived from a mantle source. The zircon UPb dating of monzonite granitic gneiss and plagioclase gneiss yields ages of 464 ± 4 Ma for and 487 ± 3 Ma, respectively. The monzonite granitic gneiss derived from the mixing of melts derived from pelitic and metaluminous rocks. The protolith of plagioclase gneiss is aplite, which has positive εHf(t) values of +5.9 ~ +7.9, indicating it derived from the lower crust sources. The monzonite granitic gneiss and plagioclase gneiss exhibit S-type and I-type geochemical features, respectively. They are geochemically similar to the volcanic arc granite. We propose that the Schladming Complex in the Eastern Alps has been a part of the active continental margin of Gondwana during Cambrian to Ordovician. With the subduction of the Proto-Tethyan Ocean to the south, a back-arc rift developed along the northern margin of the Gondwana in the Early Cambrian, subsequently, resulted in the opening of the Crypto-Rheic Ocean and the break-off of the Cadomian terrane from Gondwana in the Late Cambrian. Meanwhile, the I-type granites, related to the subduction, intruded into the northern margin of the Cadomian terrane. In the Early Ordovician the Cadomian terrane collided back to the Gondwana with the closure of the Crypto-Rheic Ocean due to the continuing southward subduction of the Proto-Tethyan Ocean. Subsequently, a number of S-type granites intruded due to the post-collisional extension during Early to Late Ordovician.

Vestiges of Cambro-Ordovician continental accretion in the Carpathian-Balkan orogen: First evidence of the 'Cenerian' event in the central Serbo-Macedonian Unit

Article

Full-text available

Jan 2021
ACTA GEOL POL

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.

The Wechsel Gneiss Complex of Eastern Alps: an Ediacaran to Cambrian continental arc and its Early Proterozoic hinterland

Article

Full-text available

Dec 2020

Many metamorphosed basement complexes in the Alps are polymetamorphic and their origin and geological history may only be deciphered by detailed geochronology on the different members including oceanic elements like ophiolites, arc successions, and continental passive margin successions. Here we present a case study on the Lower Austroalpine Variegated Wechsel Gneiss Complex and the overlying low-grade metamorphosed Wechsel Phyllite Unit at the eastern margin of Alps. The Wechsel Gneiss Complexes are known to have been overprinted by Devonian metamorphism, and both units were affected by Late Cretaceous greenschist facies metamorphism. New U–Pb zircon ages reveal evidence for two stages of continental arc-like magmatism at 500–520 Ma and 550–570 Ma in the Variegated Wechsel Gneiss Complex. An age of ca. 510 Ma of detrital zircons in metasedimentary rocks also constrain the maximum age of metasedimentary rocks, which is younger than Middle Cambrian. The overlying Wechsel Phyllite Unit is younger than 450 Ma (Late Ordovician) and seems to have formed by denudation of the underlying Variegated Wechsel Gneiss Complex. We speculate on potential relationships of the continental arc-type magmatism of the Variegated Wechsel Gneiss Complex and potential oceanic lithosphere (Speik complex) of Prototethyan affinity, which is also preserved in the Austroalpine nappe complex. The abundant, nearly uniform 2.1 Ga- and ca. 2.5 Ma-age signature of detrital zircons in metasediments (paragneiss, quartzite) of the Variegated Wechsel Gneiss Complex calls for Lower Proterozoic continental crust in the nearby source showing the close relationship to northern Gondwana prominent in West Africa and Amazonia.

Tectonic exhumation of the Central Alps recorded by detrital zircon in the Molasse Basin, Switzerland

Article

Full-text available

Nov 2020
SE

Eocene to Miocene sedimentary strata of the Northern Alpine Molasse Basin in Switzerland are well studied, yet they lack robust geochronologic and geochemical analysis of detrital zircon for provenance tracing purposes. Here, we present detrital zircon U–Pb ages coupled with rare-earth and trace element geochemistry to provide insights into the sedimentary provenance and to elucidate the tectonic activity of the central Alpine Orogen from the late Eocene to mid Miocene. Between 35 and 22.5 ± 1 Ma, the detrital zircon U–Pb age signatures are dominated by age groups of 300–370, 380–490, and 500–710 Ma, with minor Proterozoic age contributions. In contrast, from 21 Ma to ∼ 13.5 Ma (youngest preserved sediments), the detrital zircon U–Pb age signatures were dominated by a 252–300 Ma age group, with a secondary abundance of the 380–490 Ma age group and only minor contributions of the 500–710 Ma age group. The Eo-Oligocene provenance signatures are consistent with interpretations that initial basin deposition primarily recorded unroofing of the Austroalpine orogenic lid and lesser contributions from underlying Penninic units (including the Lepontine dome), containing reworked detritus from Variscan, Caledonian–Sardic, Cadomian, and Pan-African orogenic cycles. In contrast, the dominant 252–300 Ma age group from early Miocene foreland deposits is indicative of the exhumation of Variscan-aged crystalline rocks from the Lepontine dome basement units. Noticeable is the lack of Alpine-aged detrital zircon in all samples with the exception of one late Eocene sample, which reflects Alpine volcanism linked to incipient continent–continent collision. In addition, detrital zircon rare-earth and trace element data, coupled with zircon morphology and U∕Th ratios, point to primarily igneous and rare metamorphic sources. The observed switch from Austroalpine to Penninic detrital provenance in the Molasse Basin at ∼ 21 Ma appears to mark the onset of synorogenic extension of the Central Alps. Synorogenic extension accommodated by the Simplon fault zone promoted updoming and exhumation the Penninic crystalline core of the Alpine Orogen. The lack of Alpine detrital zircon U–Pb ages in all Oligo-Miocene strata corroborate the interpretations that between ∼ 25 and 15 Ma, the exposed bedrock in the Lepontine dome comprised greenschist-facies rocks only, where temperatures were too low for allowing zircon rims to grow, and that the Molasse Basin drainage network did not access the prominent Alpine-age Periadriatic intrusions located in the area surrounding the Periadriatic Line.

The early Paleozoic cumulate gabbroic rocks from the southwest part of the Tisza Mega-Unit (Mt. Papuk, NE Croatia): evidence of a Gondwana suture zone

Article

Jul 2020

The Mt. Papuk heteroadcumulate pyroxene–amphibole gabbronorites, which outcrops at the southern margin of the Tisza Mega-Unit, is suggested to stem from the deep oceanic crust formed by the in situ crystallisation in a supposed magma chamber. Amphibole oikocrystals are found to define a poikilitic texture of analysed rocks. A common enclosure in amphibole is the cumulus orthopyroxene, and rarely, the clinopyroxene and/or plagioclase and spinel. The chemical composition of related minerals and their crystallisation sequence suggest the sub-solidus crystallisation of gabbronorite in an open system at high temperatures and medium pressures. Parental magmas originated from the moderately depleted mantle source, which was metasomatised prior to melting. Early mineral fractionation gave rise to the assemblage consisted of spinel, pyroxene, plagioclase and intercumulus amphibole. The rocks’ bulk chemistry, mineral crystallisation sequence, pyroxene geochemistry and myriad of high Ca-plagioclase, which coexists with igneous Ca-amphibole are all in favour of the strong subduction influence typical for mafic intrusion formed above mantle wedge in the root of an island arc at depths of 10–21 km. Herein presented geochemical and isotopic data (40Ar–39Ar: 487.1 ± 4.3 Ma and Sm–Nd: 505 Ma) go along with the existence of an intra-oceanic arc related to geodynamic events that took place in the Prototethyan oceanic realm s.l. during middle Cambrian to earliest Ordovician. These events were likely correlated with the subduction of the Quaidam(?) back-arc ocean, or alternatively, with the subduction and closure of Prototethyan branches located between microcontinental fragments of Asia. Initially, the closure of back-arc oceans led to crust fragmentation and, then, addition of non-metamorphosed mafites into the obducted sequence further from the active continental margins of Gondwana and Laurassia at the time of the formation of Pangea in the late Palaeozoic.

Ordovician mafic magmatism in an Ediacaran arc complex, Sibak, NE Iran: the eastern tip of the Rheic Ocean

Article

Jul 2018
CAN J EARTH SCI

The assembly of Gondwana in the Ediacaran was concluded by extensive arc magmatism along its northern margin. Extensional events in the early Paleozoic led to rifting and the eventual separation of terranes, which were later assimilated in different continents and orogens. The Sibak area of northeastern Iran records these events, including late Precambrian volcanic-sedimentary processes, metamorphism, and magmatism. A granite at Chahak in the Sibak Complex yields a zircon U–Pb age of 548.3 ± 1.1 Ma, whereas a spatially associated gabbro has an age of 471.1 ± 0.9 Ma. The latter corresponds to the earliest stages of rifting in the nearby Alborz domain, with the deposition of clastic sedimentary sequences, basaltic volcanism, and, as indicated by indirect evidence, coeval granitic plutonism. The Chahak gabbro is thus one of the earliest witnesses of the rifting processes that eventually led to the development of the Rheic Ocean and were indirectly linked to subduction of Iapetus at the Laurentian margin and the early development of the Appalachian orogen.

Lithium pegmatite of anatectic origin – A case study from the Austroalpine Unit Pegmatite Province (Eastern European Alps): Geological data and geochemical modeling

Article

Full-text available

Jan 2023
ORE GEOL REV

There is an ongoing debate as to whether rare element pegmatite is always related to fractional crystallization of huge fertile granite bodies or whether it can also form directly from limited portions of enriched anatectic melt. In this contribution, we present a case study from the Eastern European Alps, showing the continuous evolution from melt generation in staurolite bearing micaschist to spodumene (LiAlSi2O6) bearing pegmatite. The investigated Austroalpine Unit Pegmatite Province formed during Permian lithospheric extension and all levels of the Permian crust are now accessible in a Cretaceous nappe stack. This nappe stack is mapped in detail, subdivided lithostratigraphically and the internal tectonic structure is well understood. It is clear that the described pegmatites are neither spatially nor genetically related to large fertile granite bodies. A review of geochronological data proofs that emplacement of pegmatite and leucogranite is broadly contemporaneous with high temperature-low pressure metamorphism of the country rocks. Field observations give clear evidence of a genetic link between simple pegmatite, leucogranite, evolved pegmatite and albite-spodumene pegmatite, on the one hand, and the subsolidus or suprasolidus metasediment hosting them on the other hand. These relations are underpinned by geochemical major and trace element investigations on all types of rock and the minerals therein. As source rock an Al-rich metapelite enriched in Li (70-270 ppm) with respect to the average upper continental crust is identified. The main Li-carrier is staurolite with up to 3000 ppm Li. The pegmatite and leucogranite originate in anatectic melts that formed between 0.6-0.8 GPa and 650-750°C, corresponding 18-26 km depth. During melt formation staurolite was consumed by sillimanite forming reactions. Subsequently, the melts were enriched in Li by fractional crystallization of quartz and feldspar during their ascent to higher crustal levels. While simple pegmatite and inhomogeneous leucogranite formed in lower and intermediate levels, evolved and albite-spodumene pegmatite crystallised at high levels at conditions between 0.3-0.4 GPa and 500-570°C, corresponding to about 12 km depth. Based on these data we develop a geochemical model for showing that Li can be transferred from a metasediment into an anatectic melt if staurolite is stable or metastable at the onset of melting. Such a melt can contain between 200 and 1000 ppm Li and the melt can be further enriched with up to 5000 to 10000 ppm Li through fractional crystallization of quartz and feldspar, allowing crystallization of spodumene. Estimated fractionation degrees vary between 81 and 99%, depending on the protolith composition, the melting scenario and the partitioning coefficients. Li-Al-rich metasediments are therefore a rich source of certain rare elements when they first melt. However, the spectrum of elements contained in the melt depends on a wide variety of conditions. This anatectic model provides an alternative explanation for the formation of Li-rich pegmatite if no fertile parent granite can be identified.

U-Pb zircon (ID-TIMS and SHRIMP) evidence for the early ordovician intrusion of metagranites in the late Proterozoic Canaveilles Group of the Pyrenees and the Montagne Noire (France)

Article

Full-text available

May 2005

Geological and Tectonic Setting of Austria

Chapter

May 2022

The landforms of Austria are the direct consequence of a continuous interplay between tectonic and climatic forces that have built, destroyed and reshaped the surface of the most iconic mountain belt on Earth for almost 40 Million years. As such, landforms can only be understood with a thorough geological background. This paper gives an overview of the tectonic evolution, the geological build up and the landscape evolution in the Austrian territory. The tectonic evolution of the rocks forming the major tectonic units of Austria can be traced back to some 500 Million years when they were located at different ancient continents including Gondwana, Avalonia and Laurasia. In the late Palaeozoic, the basement rocks were affected by the Variscan tectonometamorphic event during amalgamation of the supercontinent Pangaea and by a Permian extensional event. The latter is responsible for and was followed by a long-lived phase of thermal subsidence triggering the deposition of the Mesozoic sedimentary pile of the Northern Calcareous Alps. The formation and later subduction of the Neotethys and Penninic oceans began in Triassic and Jurassic times, respectively. The Alpine orogen as we know it today is largely the consequence of the head-on collision between the Adriatic and European plates once subduction had terminated around 40 Ma. The geological build up of Austria includes the Alps and its northern foreland. The foreland is composed of Variscan gneisses in the Bohemian Massif, their Mesozoic cover and Cenozoic sediments in the Molasse Basin. The Alps are made up of tectonic units derived from the European and Adriatic continents and the Neotethys and Penninic oceans that are covered by some intramontane and marginal basins that are filled with Neogene sediments. The landscape evolution evolved since the Oligocene and is highly influenced by processes in the mantle. It involved the interplay of many kilometres of rock uplift and simultaneous erosion so that few rocks at the surface today can be traced back to this time. Nevertheless, low-temperature geochronology, a series of fossil relict surfaces and enigmatic deposits like the Augenstein Formation on the plateaus of the Northern Calcareous Alps testify of a stepwise formation of the landscape over the last 25 Million years. Current research shows that up to 500 m of surface uplift may have occurred in the last 5 Million years alone.KeywordsAustriaGeologyGeodynamicsPalaeogeographyMantle structureLandscape evolution

Opening of the West Paleo-Tethys Ocean: New insights from earliest Devonian meta-mafic rocks in the Saualpe crystalline basement, Eastern Alps

Article

Full-text available

May 2021
GONDWANA RES

The timing of the opening of the West Paleo-Tethys Ocean in Eastern Alps remains unclear. To constrain this event, we present new zircon U-Pb ages, Hf isotopic compositions, and whole-rock major- and trace-element data for the meta-mafic rocks (amphibolites) in the southern and western Saualpe crystalline basement, Eastern Alps. Zircon U-Pb dating of three samples yield crystallization ages of 418 ± 6 Ma, 417 ± 3 Ma and 415 ± 3 Ma, indicating that they formed during the earliest Devonian. Geochemically, these meta-mafic rocks have relatively low SiO2 and MgO contents and high TiO2 contents. They are enriched in light rare earth elements (LREE), particularly in Nb and Ta, and show relatively flat heavy rare-earth elements (HREE) patterns, suggesting that they have affinities with the alkaline oceanic island basalts (OIB). The geochemical characteristics, together with the positive εHf(t) values of 0.7–11.1, imply that the OIB-like meta-mafic rocks originated from partial melting of a lherzolite source including spinel and garnet. The primary magma shows complex sources involving asthenospheric, lithospheric mantle and subducted slab components, which was subsequently modified by crustal contamination. This reveals that the magma formed in a slab window environment associated with mid-ocean ridge subduction. The contemporaneous OIB-like alkaline amphibolites were also found in the Central Austroalpine basement and in Northwestern Turkey. We suggest that the Late Silurian–earliest Devonian OIB-like magmatism is related to a back-arc extension setting along the northern margin of Gondwana leading to the separation of the European Hunic terranes and hence placing age constraints on the opening of the West Paleo-Tethys Ocean.

Traçage des sédiments dans les séries syn-orogéniques du bassin d'Aquitaine

Thesis

Jun 2020

Stéphane M. Al Reda

La dynamique de formation d’une chaîne de montagne peut être reconstruite à partir de l’étude des bassins réceptacles des produits d’érosion. Les travaux présentés ont été réalisés dans la partie orientale du Bassin d’Aquitaine (Corbières), à partir de l’étude de la série de Palassou. Ces sédiments, en majorité conglomératiques, traduisent une phase d’érosion majeure des reliefs, accompagnant la continentalisation des bassins au cours de l’Yprésien et la période de raccourcissement principal de l’orogenèse pyrénéenne. Trois unités tectono-stratigraphiques ont été défini dans cette série : l’unité 1 - Yprésien supérieur-Lutétien – caractérisée par la présence de galets Méso-Cénozoïques, l’unité 2 – Bartonien – caractérisée par la présence des galets de socle et l’unité 3 – Priabonien- caractérisée par la présence à nouveau de galets Méso-Cénozoïques. L’objectif de cette thèse est de comprendre le mode de remplissage du bassin d’avant-pays nord pyrénéen et son évolution au cours de l’Éocène. Ceci permettra d’appréhender la formation des reliefs à l’intérieur de la chaîne et de caractériser les différentes sources d’apport. Trois approches ont été utilisées pour reconstruire le routage des sédiments dont la première est l’étude sédimentaire et la caractérisation des environnements de dépôts des deux premières unités. Les résultats obtenus montrent l’identification de quatre séquences de remplissage sédimentaire dans l’unité 1, dont l’essentiel s’est déposé dans le synclinal de Talairan jusqu’à son débordement au cours du dépôt de la troisième séquence. Ceci amène à interpréter le synclinal de Talairan comme un bassin en piggy back. La deuxième approche est la thermochronologie basse température appliquée sur des clastes de granites issus de l’unité 2. Les résultats de traces de fission sur apatite montrent des âges plus jeunes d’est en ouest alors que les résultats de (U-Th-Sm)/He sur apatite montrent une dispersion des âges. La modélisation thermique de ces résultats indique un réchauffement post-Bartonien, traduisant une série sédimentaire plus épaisse au moment du dépôt puis partiellement érodée. La phase d’érosion est estimée comme pré-Langhienne suite aux résultats de modélisation thermique et des contraintes stratigraphiques. La troisième approche utilisée au cours de cette thèse est la datation U/Pb sur zircon. Des échantillons de matrice de conglomérat ainsi que des galets de granite issus des trois unités ont fait l’objet d’étude par cette approche. Les résultats obtenus montrent un signal Varisque majeur. Ils ont été couplés avec des analyses Raman et des directions de paléo-courant mesurés afin de caractériser les sources des sédiments pour chaque unité. Les dépôts de l’unité 1 sont issues de la Zone Nord Pyrénéenne. Les dépôts de l’unité 2 ont comme source la Zone Axiale des Pyrénées alors que les dépôts de l’unité 3 présentent un spectre d’âges assez large dont la source est la partie orientale et centrale des Pyrénées. Ces résultats ont permis de reconstruire le cheminement des sédiments dans les Corbières au cours de l’Éocène.

Gondwana fragments in the Eastern Alps: A travel story from U/Pb zircon data

Article

Aug 2019
GONDWANA RES

We compare detrital U/Pb zircon age spectra of Carboniferous and Permian / Lower Triassic sedimentary rocks from different structural positions within the Austroalpine nappe pile with published ages of magmatic and metamorphic events in the Eastern Alps and the West Carpathians. Similarities between sink and possible sources are used to derive provenance of sediments and distinct frequency peaks in sink and source age pattern are used for paleogeographic plate tectonic reconstructions. From this, travel paths of Austroalpine and West Carpathian basement units are traced from the Late Neoproterozoic to the Jurassic. We place the ancestry of basement units on the northeastern Gondwana margin, next to Anatolia and the Iranian Luth-Tabas blocks. Late Cambrian rifting by retreat of the Cadomian Arc failed and continental slivers re-attached to Gondwana during a late Cambrian / early Ordovician orogenic event. In the Upper Ordovician crustal fragments of the Galatian superterrane rifted off Gondwana through retreat of the Rheic subduction. An Eo-Variscan orogenic event at ~390 Ma in the Austroalpine developed on the northern rim of Galatia, simultaneously with a passive margin evolution to the south of it. The climax of Variscan orogeny occurred already during a Meso-Variscan phase at ~350 Ma by double-sided subduction beneath Galatia fragments. The Neo-Variscan event at ~330 Ma was mild in eastern Austroalpine units. This orogenic phase was hot enough to deliver detrital white mica into adjacent basins but too cold to create significant volumes of magmatic or metamorphic zircon. Finally, the different zircon age spectra in today's adjacent Carboniferous to Lower Triassic sediments disprove original neighbourhood of basins. We propose lateral displacement of major Austroalpine and West-Carpathian units along transform faults transecting Apulia. The intracontinental transform system was released by opening of the Penninic Ocean and simultaneous closure of the Meliata Hallstatt Ocean as part of the Tethys.

Primordial geodynamics of Southern Carpathian-Balkan basements (Serbo-Macedonian Mass): Avalonian vs. Cadomian arc segments

Article

Full-text available

Dec 2018
P GEOLOGIST ASSOC

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

Geochronology, petrogenesis, and tectonic setting of amphibolitic rocks from the Tutak metamorphic Complex, Sanandaj-Sirjan Zone, Iran

Article

Jun 2023

Early Paleozoic mafic intraplate magmatism in the Binaloud zone, NE Iran: Implications for the long-lived mantle plume activity in the northern margin of Gondwana

Article

Apr 2023
LITHOS

Documentation of continental rifting processes such as mantle plume activity is important for understanding the nature and evolution of tectonic plates. In this study, we report detailed petrological, geochronological, geochemical, Srsingle bondNd isotope, and mineral chemical data for basalt, and coarse- and fine-grained gabbro from the Binaloud zone of the Alborz, which is the easternmost extension of the Avalonian-Cadomian Orogenic Belts and the western parts of Indo-Australia Orogenic Belt, central-east Asia. Uranium–lead zircon dating of fine- and coarse-grained gabbro indicates that they have been formed at 461.8 ± 8.2 and 435.0 ± 4.5 Ma, respectively. The basalt and gabbro have large variations in elemental and isotopic compositions, with 44.0–50.0 wt% SiO2, 124–411 ppm Sr, and εNd(t) of +0.1 to +3.3. All the rocks show OIB-like or transitional OIB−/E-MORB-like geochemical characteristics, without noticeable Nbsingle bondTi depletion, diagnostic of an intraplate affinity. Whole-rock geochemical and isotopic compositions combined with mineral compositions suggest that both basalt and gabbro have been generated by a plume/asthenospheric mantle (OIB-type) source mixed with enriched subcontinental lithospheric mantle components. Partial melting of such a source in the transitional spinel-garnet stability field was followed by different degrees of fractional crystallization of olivine, clinopyroxene, and plagioclase. Our study demonstrates that roll-back of the subducting Tornquist (Eastern Ipateous ocean) oceanic lithosphere has been followed by plume activity, continental rifting and Paleo-Tethys opening during the Silurian period.

Tracing the protoliths of the garnet amphibolitic and retrogressed eclogitic slices and a conceptual tectonic model for their emplacement onto the Central Menderes Massif, Turkey: New geochemical data and laser ablation-inductively coupled plasma-mass spectrometry U-Pb zircon and rutile ages

Article

Aug 2023
GEOL SOC AM BULL, GSA Bulletin

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.

Combined U-Pb ages and Lu-Hf systematics of detrital zircons from Early Cambrian Gondwanan siliciclastic rocks in S Turkey: Provenance and correlations with coeval successions in peri-Gondwanan terranes

Article

Apr 2022
GONDWANA RES

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.

Birth of the Alps - Siegesmund-etal-2021-IJES

Article

Full-text available

Apr 2022

Abstract New whole-rock geochemical and coupled U–Pb and Lu–Hf LA-ICP-MS zircon data of metasedimentary rocks of the Austroalpine, South Alpine and Penninic basement domains are presented, to disentangle the pre-Variscan tectonic evolution of the proto-Alps. The studied units seem to record distinct stages of protracted Late Ediacaran to Carboniferous tectonosedimentary processes prior to the Variscan collision. In the case of Austroalpine and South Alpine units, nevertheless, no major differences in terms of provenance are observed, since most detrital zircon samples are characterized by a major Pan-African peak. Their detrital zircon spectra record a provenance from the northeastern Saharan Metacraton and the Sinai basement at the northern Arabian-Nubian Shield, being thus located along the eastern Early Paleozoic northern Gondwana margin, whereas sources located further west are inferred for the Penninic Unit, which might have been placed close to the Moldanubian Unit of the Bohemian Massif. In any case, it is thus clear that the Alpine basement remained in a close position to the Gondwana mainland at least during the Early Paleozoic. The Late Ediacaran to Silurian tectonic evolution, which includes Cadomian and Cenerian tectonometamorphic and magmatic processes, seem thus to record a continuum related to a retreating-mode accretionary orogen, with diachronous back-arc basin opening and possibly discrete compressional/ transpressional pulses linked to changes in subduction zone dynamics. On the other hand, it is inferred that the Alpine basement essentially comprises Pan-African metasedimentary and subordinate metaigneous rocks, possibly with very few Early Neoproterozoic relics. This basement was significantly reworked during the protracted Paleozoic orogenic evolution, due to anatexis and/or assimilation by mantle-derived juvenile magmatism.

Geochronology and geochemistry of the Ediacaran orthogneisses from the north Shahrekord ( Sadegh‐Abad ), Sanandaj‐Sirjan Zone: Insights into magmatic evolution of the Iranian basement

Article

Mar 2022

The metamorphosed Sadegh‐Abad granite from the north Shahrekord Metamorphic Complex (NSMC) of Sanandaj‐Sirjan Zone in west Iran shows evidence of ductile deformation. The augen to banded mylonitic granite (orthogneiss) involves sharp contacts with other rock units, including high‐grade metamorphic rocks, such as eclogite, amphibolite, and garnet amphibolite as well as schists. U–Pb zircon dating reveals that the crystallization of the granitic magma occurred at 568 ± 14 Ma (Late Neoproterozoic, Ediacaran). The Sadegh‐Abad mylonitic granite comprises high SiO2 (67–78 wt.%) and Na2O (3.23–7.79 wt.%) contents and low CaO (0.73–1.61 wt.%) and variable K2O concentrations (0.08–4.6 wt.%). The chondrite‐normalized REE diagram shows enrichment in LREE relative to HREE (Ce/Yb)N = 1.90 to 6.12), a negative Eu anomaly (Eu/Eu* = 0.10–0.66), and nearly flat HREE patterns (Tb/Yb)N = 0.94–1.44). These are interpreted to have originated from a continental crustal source. This is further supported by the high concentration of the alkali elements, U, Th, Rb, and the high 87Sr/86Sr(i) isotopic ratios (0.7086 to 0.7163). The lower HREEs abundances, negative Eu anomalies, and the low contents of mafic minerals may infer that partial melting of continental crust has taken place in low‐pressure conditions within the plagioclase stability field, possibly of pre‐existing calc‐alkaline bodies in the lower continental crust. The charge of heating probably occurred via the injection of mafic magmas into the tonalitic and granodioritic continental crust. The Middle East portion of the Alpine–Himalayan orogenic belt with locations of dated Late Neoproterozoic‐Cambrian plutonic rocks, including Sadegh‐Abad orthogneisses of Iran.

Geochronology and petrogenesis of the Late Neoproterozoic granitic gneisses of Golpayegan metamorphic complex: a new respect for Cadomian crust in the Sanandaj-Sirjan zone, Iran

Article

Sep 2020
INT GEOL REV

The studied granitic gneiss bodies of the Golpayegan metamorphic complex, located in the central part of the Sanandaj Sirjan Zone (SaSZ), in western Iran. Zircon U-Pb dating of two samples shows that the crystallization of the protolith occurred at 557 ± 12 Ma in the Late Neoproterozoic (Ediacaran), broadly coeval to the Neoproterozoic-Early Palaeozoic basement in other parts of Iran. Geochemically, the protolith of the gneisses probably corresponds to differentiated I-type granites with subalkaline affinities in composition. The ratios of Y/Nb >1.2 reveal an affinity to Cordilleran I-type granites for the granitic gneisses. The high Th/U ratios (2.8 to 9), low Eu/Eu* (0.13 to 0.73), with, low contents of FeO (0.55 to 1.72 wt.%), MgO (0.07 to 0.53 wt.%) and MnO (0.01 to 0.04 wt.%) and the high 87Sr/86Sr(i) ratios (0.70693 to 0.73557), negative ƐNd(t) values (−4.4 to −1.7) and Nd model ages (TDM2 = 1.35 to 1.56 Ga) suggest that the protolith may have been derived from partial melting of a pre-existing felsic crustal source (most likely differentiated granitoids). The new results reveal that the granitic source magma has been evolved in an active continental margin tectonic regime during the southward subduction of the Proto-Tethys ocean beneath the northern margin of Gondwana, like other coeval fragments dispersed in the entire Cadomian active continental margins. Also, the Cadomian crust widely extended in western Iran and it confirms these rocks have some clear affinity with Cadomian crust in the world.

Reconstructing the Variscan Terranes in the Alpine Basement: Facts and Arguments for an Alpidic Orocline

Article

Full-text available

Jan 2022

The existence of pieces of the Variscan belt in the Alpine basement has been acknowledged for a long time but the correlation of these massifs to the litho-tectonic domains established in Western Europa outside the Alpine chain is still disputed. Due to their ubiquitous character, the abundant late Variscan migmatites and granites are useless to reconstruct the Variscan architecture in the Alpine basement. Ophiolitic sutures, high- and low-grade metamorphic units, and foreland basins provide a preliminary reconstruction of the Variscan orogen exposed in the Alpine basement. The longitudinal extension of the Armorican and Saxo-Thuringian microcontinents between Laurussia and Gondwana is proposed independently of the Intra-alpine and Galatian terranes. The litho-tectonic units of the Corsica-Sardinia segment are correlated to the Moldanubian, Armorican and Saxo-Thuringian Domains. In the Alpine Helvetic and Penninic Domains, the Chamrousse ophiolites are ascribed to the Tepla-Le Conquet suture, whereas the Lepontine, and Stubach ophiolites represent the Rheic suture. The south-directed nappe stack of the South Alpine Domain is similar to the Moldanubian French Massif Central. In the Austroalpine nappe stack, the Ritting ophiolites separate Saxo-Thuringia and Armorica continental blocks. Disentangling the Variscan belt in the Alpine basement suggests a concave-to-the-East arcuate structure called here the Variscan Alpidic orocline.

Pre-Alpine tectonic evolution of the Eastern Alps: From Prototethys to Paleotethys

Article

Jan 2022
EARTH-SCI REV

In all reconstructions published during the last two decades, the Austroalpine and the correlative Southalpine basement units of the Eastern Alps were considered to represent a uniform continental block that split off from the northern Gondwana margin during Early Paleozoic times and collided with microcontinental blocks during the Variscan orogeny in the early Late Carboniferous. Afterwards, these units formed finally the outboard part of the European Variscides adjacent to the Paleotethys Ocean. The combined Austroalpine/Southalpine basement extends to the Western Carpathians, contains Ediacaran and Early Paleozoic ophiolites and magmatic arcs and Devonian passive margin successions and represents a key region for resolving the Late Neoproterozoic to Late Paleozoic tectonic evolution of the basement in the Alpine-Mediterranean Mountain belts. The Austroalpine and Southalpine basement contains well-known fossil-rich Ordovician and Silurian rift and mainly Devonian passive margin successions summarized as the Noric and Carnic domains, which were juxtaposed to amphibolite-grade metamorphic complexes during Early Carboniferous plate collision. In the metamorphic units the following main stages of tectonic evolution are. Two distinct Ediacaran to Cambrian arc systems were recognized, correlating with subduction of the Prototethys (Ran) Ocean. The continental Wechsel Arc stopped its activity during Late Cambrian times, whereas the Silvretta-Gleinalpe Arc was reactivated at the Devonian/Carboniferous boundary during subduction of the Devonian Balkan-Carpathian Ocean. The Prototethyan oceanic crust is preserved in the ophiolitic Upper Neoproterozoic to Middle Ordovician Speik Complex, that was obducted onto the Silvretta-Gleinalpe Arc during Late Ordovician to Early Silurian times. On the other hand, the Noric domain was initially part of the northern Gondwana margin and includes a virtually continuous sedimentary section ranging from the Early Ordovician to earliest Pennsylvanian. It started with an Early to Late Ordovician rift succession with mafic and acidic volcanic rocks related to rifting of parts of the Noric domain from the northern Gondwana margin forming an oceanic basin (Rheic of previous interpretations) in between and back-arc rifting is the likely setting. In both Noric and Carnic domains, Silurian strata were deposited during a tectonically quiet period followed by onset of a second rifting period during Late Silurian times, which resulted in deposition of thick Devonian carbonates heralding the opening of the Balkan-Carpathian Ocean and separation of the Paleo-Adria microcontinent from Gondwana. Late Devonian–Carboniferous plate convergence led to subduction of this oceanic rift followed by subduction of the Paleo-Adria margin underneath the accreted Variscan convergence belt, collision and Late Carboniferous intramontane molasse deposition. However, new data argues that a third ophiolitic belt, the Plankogel ophiolitic mélange, which formed as part of the Paleotethys Ocean during the Devonian and was reactivated as trench during initial consumption of the Paleotethys Ocean during Late Permian–Triassic times. The Middle-Late Triassic plutonic and volcanic rocks of the Southern Alps are considered, in this preliminary model, to represent the magmatic arc associated with Paleotethys subduction.

Petrochronology of Monazite-Bearing Garnet Micaschists as a Tool to Decipher the Metamorphic Evolution of the Alpine Basement

Article

Full-text available

Sep 2021

Bernhard Schulz

Garnet-bearing metapelites in the Helvetic and Austroalpine pre-Mesozoic polymetamorphic basement are characterised by pressure-temperature path segments reconstructed by microstructurally controlled geothermobarometry, and the Th-U-Pb monazite age distribution pattern revealed by the electron probe microanalyser (EPMA). In the Helvetic Aiguilles Rouges Massif and the Austroalpine Oetztal-Stubai basement to the NW an Ordovician-to-Silurian high temperature event preceded a pressure-dominated Carboniferous metamorphism. In the Austroalpine basement units to the south of the TauernWindow, the maximal pressures of the Carboniferous amphibolite-facies metamorphism range from 12 to 6 kbar. The decompressional P-T path segments signal a transition to low pressure conditions. A subsequent high pressure overprint is restricted to the Prijakt Subgroup unit in the Schobergruppe and documented by Cretaceous monazite crystallisation at 88 +- 6 Ma. In the Austroalpine Saualpe basement to the SE, a distinct early Permian metamorphism which started at low pressures of ~4 kbar/500 °C and reached maximal 6 kbar/600–650 °C predated the intrusion of Permian pegmatites. Permian monazite crystallised in line with the intrusion of pegmatites. Corona microstructures around the Permian monazites indicate retrogression previous to a Cretaceous high pressure metamorphism. That way, pressure-temperature-time paths resolve the spatial and temporal evolution in the polymetamorphic Alpine basement prior to the Tertiary collision.

Hf isotopic constraints and detrital zircon ages for the Austroalpine basement evolution of Eastern Alps: Review and new data

Article

Aug 2021
EARTH-SCI REV

The Alps, as part of the Alpine-Mediterranean Mountain chain, are one of the classical localities for orogenic studies, where the Mesozoic-Cenozoic tectonic evolution is well known, and many classical models have been proposed to explain the tectonic evolution from Mesozoic rifting and breakup to Late Mesozoic-Cenozoic subduction, plate collision, and exhumation. However, the pre-Mesozoic tectonic evolution of the pre-Alpine basement remains poorly known because of the lack of sufficient age data due to complex polyphase deformation and multiple metamorphic overprints. New data from the mainly amphibolite-facies pre-Alpine basement of the Austroalpine mega-unit indicates that this basement is composed of a heterogeneous series of continental units, island arcs, ophiolites, subduction mélanges, accretionary wedges, and seamounts affected by different metamorphic grades. This study presents new results of LA-ICP-MS U-Pb dating and MC-ICP-MS Lu-Hf isotopic tracing of zircons from three key areas of Austroalpine basement, including the: i) Wechsel Gneiss and Waldbach Complexes, and Wechsel Phyllite Unit, (ii) Saualpe-Koralpe-Pohorje, and (iii) Schladming-Seckau areas. We determine the Wechsel Gneiss Complex to be a continental magmatic arc formed during 500–560 Ma in the proximity to a continental block with a ‘memory’ of Late Archean to Early Proterozoic continental crust. The Wechsel Gneiss Complex has Hf model ages of 2.1 to 2.2 Ga and 2.5 to 2.8 Ga that indicate a close relationship to northern Gondwana, with depleted mantle Hf model ages as old as 3.5 Ga. The Wechsel Phyllite Unit structurally overlying the Wechsel Gneiss Complex has partly different sources, including juvenile crust formed at ca. 530 Ma. In contrast, the Waldbach Complex constantly added new crustal material during the 490–470 Ma period and bears considerably more positive εHf(t) values than the underlying Wechsel Gneiss Complex and gives relatively young, depleted mantle model ages of 700 to 500 Ma. The Waldbach Complex is, therefore, interpreted to be part of a magmatic arc that formed during closure of the Prototethys and was metamorphosed during Variscan orogenic events at ca. 350–330 Ma. The Schladming-Seckau and Wechsel Complexes represent a Cambro-Ordovician magmatic arc system formed by Prototethys subduction processes with the associated Late Neoproterozoic to Early Ordovician ophiolitic Speik complex having formed in its back-arc basin or as Prototethyan lithosphere. The Plankogel Complex and structurally overlying micaschist and amphibolite units represent accreted ocean, ocean island, and continent-derived materials, interpreted to be an accretionary complex formed during the Permo-Triassic closure of the Paleotethys. Many granites with Permian ages (e.g., porphyric granite called Grobgneiss and other granite gneisses and associated pegmatites) were likely formed in an extensional environment that culminated in the opening of the Middle-Late Triassic Meliata oceanic rift. These granites formed by partial remelting of crust with mainly Middle Proterozoic Hf model ages. Taken all these data together, we find that the Austroalpine basement is heterogeneously composed and includes complexes of different ages, different tectonic evolutionary histories and different remolten sources representing different locations before final accretion. The composite of pre-Alpine complexes in the Austroalpine mega-unit likely assembled not earlier than Late Permian or Early Triassic.

Zircon U-Pb-Hf snapshots on the crustal growth of the Serbomacedonian massif: New insights from the Ammouliani island (Northern Greece)

Article

Full-text available

Aug 2021

Konstantinos Papapavlou

Zircon U–Pb and Lu–Hf isotope microanalysis was conducted in (meta)-igneous units of Ammouliani island to characterize crust-forming and reworking events in the Serbo-Macedonian massif. Zircon grains from an orthogneiss of the Vertiskos unit yielded a U–Pb crystallization age for the igneous precursor at 458.8 ± 11 Ma with dominantly subchondritic ϵHf values indicating reworking of Neoproterozoic basement. A weighted mean ϵHf value of 0.7 ± 2.4 from oscillatory zoned zircon grains of the Ouranoupoli granodiorite indicates juvenile crustal input at 52.1 ± 0.6 Ma. The U–Pb–Hf zircon archive records discrete stages in the crustal evolution of the Serbo-Macedonian massif.

The birth of the Alps: Ediacaran to Paleozoic accretionary processes and crustal growth along the northern Gondwana margin

Article

Full-text available

May 2021
INT J EARTH SCI

New whole-rock geochemical and coupled U–Pb and Lu–Hf LA-ICP-MS zircon data of metasedimentary rocks of the Austroalpine, South Alpine and Penninic basement domains are presented, to disentangle the pre-Variscan tectonic evolution of the proto-Alps. The studied units seem to record distinct stages of protracted Late Ediacaran to Carboniferous tectonosedimentary processes prior to the Variscan collision. In the case of Austroalpine and South Alpine units, nevertheless, no major differences in terms of provenance are observed, since most detrital zircon samples are characterized by a major Pan-African peak. Their detrital zircon spectra record a provenance from the northeastern Saharan Metacraton and the Sinai basement at the northern Arabian-Nubian Shield, being thus located along the eastern Early Paleozoic northern Gondwana margin, whereas sources located further west are inferred for the Penninic Unit, which might have been placed close to the Moldanubian Unit of the Bohemian Massif. In any case, it is thus clear that the Alpine basement remained in a close position to the Gondwana mainland at least during the Early Paleozoic. The Late Ediacaran to Silurian tectonic evolution, which includes Cadomian and Cenerian tectonometamorphic and magmatic processes, seem thus to record a continuum related to a retreating-mode accretionary orogen, with diachronous back-arc basin opening and possibly discrete compressional/transpressional pulses linked to changes in subduction zone dynamics. On the other hand, it is inferred that the Alpine basement essentially comprises Pan-African metasedimentary and subordinate metaigneous rocks, possibly with very few Early Neoproterozoic relics. This basement was significantly reworked during the protracted Paleozoic orogenic evolution, due to anatexis and/or assimilation by mantle-derived juvenile magmatism.

Geochronology, geochemistry and tectonic setting of the Cadomian (Ediacaran–Cambrian) magmatism in the Istranca (Strandja) Massif: new insights into magmatism along the northern margin of Gondwana in NW Turkey

Article

Full-text available

Mar 2021

Tracing proto-Rheic - Qaidam Ocean vestiges into the Western Tatra Mountains and implications for the Palaeozoic palaeogeography of Central Europe

Article

Full-text available

Dec 2020
GONDWANA RES

Zircon petrochronology from amphibolites and retrogressed eclogites from the basement of the Western Tatra Mountains (Central Western Carpathians) reveals a complex rock evolution. An island-arc related basaltic amphibolite from Žiarska Valley shows three distinct zircon forming events: igneous zircon growth at ca. 498 Ma (Middle/Late Cambrian) and two phases of amphibolite-facies metamorphism at ca. 470 Ma (Early Ordovician) and at ca. 344 Ma (Early Carboniferous). A retrogressed eclogite from Baranèc Mountain records two zircon forming events: metamorphic zircon growth under eclogite-facies conditions at ca. 367 Ma (Late Devonian) and amphibolite-facies metamorphism at ca. 349 Ma (Early Carboniferous). These data contribute towards understanding and correlating major tectonothermal events that shaped the eastern margin of Gondwana in the Early Palaeozoic and its subsequent Variscan evolution. The metabasites record vestiges of two completely independent oceanic domains preserved within the Central Western Carpathians: (1) An Ediacaran to Cambrian oceanic arc related to the proto-Rheic - Qaidam oceans and metamorphosed to amphibolite-facies in the Early Ordovician subduction of the proto-Rheic - Qaidam arc during the Cenerian orogeny (ca. 470 Ma) and (2) Late Devonian oceanic crust related to a back-arc basin (Pernek-type), formed by the opening of the Paleotethys and metamorphosed to eclogite-facies during Devonian subduction (ca. 367 Ma). The common Variscan and later evolution of these oceanic remnants commenced with amphibolite-facies metamorphic overprinting in the Early Carboniferous (amphibolite: ca. 344 Ma; retrogressed eclogite: ca. 349 Ma) related to an Early Variscan consolidation and the formation of Pangea. None of the investigated rocks of the Central Western Carpathians show any evidence of being chronologically or palaeogeographically related to the Rheic Ocean, therefore any prolongation of the Rheic suture from the Sudetes into the Alpine-Carpathian realm is highly problematic. Instead, the Southern and Central Alpine Cenerian orogeny can be traced into the Central Western Carpathians.

Geochronology and petrogenesis of the Late Neoproterozoic granitic gneisses of Golpayegan metamorphic complex: a new respect for Cadomian crust in the Sanandaj-Sirjan zone, Iran

Article

Sep 2020
INT GEOL REV

The studied granitic gneiss bodies of the Golpayegan metamorphic complex, located in the central part of the Sanandaj Sirjan Zone (SaSZ), in western Iran. Zircon U-Pb dating of two samples shows that the crystallization of the protolith occurred at 557 ± 12 Ma in the Late Neoproterozoic (Ediacaran), broadly coeval to the Neoproterozoic-Early Palaeozoic basement in other parts of Iran. Geochemically, the protolith of the gneisses probably corresponds to differentiated I-type granites with subalkaline affinities in composition. The ratios of Y/Nb >1.2 reveal an affinity to Cordilleran I-type granites for the granitic gneisses. The high Th/U ratios (2.8 to 9), low Eu/Eu* (0.13 to 0.73), with, low contents of FeO (0.55 to 1.72 wt.%), MgO (0.07 to 0.53 wt.%) and MnO (0.01 to 0.04 wt.%) and the high 87 Sr/ 86 Sr (i) ratios (0.70693 to 0.73557), negative ƐNd (t) values (−4.4 to −1.7) and Nd model ages (T DM2 = 1.35 to 1.56 Ga) suggest that the protolith may have been derived from partial melting of a pre-existing felsic crustal source (most likely differentiated granitoids). The new results reveal that the granitic source magma has been evolved in an active continental margin tectonic regime during the southward subduction of the Proto-Tethys ocean beneath the northern margin of Gondwana, like other coeval fragments dispersed in the entire Cadomian active continental margins. Also, the Cadomian crust widely extended in western Iran and it confirms these rocks have some clear affinity with Cadomian crust in the world.

Drainage response to Arabia-Eurasia collision: Insights from provenance examination of the Cyprian Kythrea flysch (Eastern Mediterranean Basin)

Article

Apr 2020

The Cenozoic geodynamics of the northeastern Mediterranean Basin have been dominated by the subduction of the African Plate under Eurasia. A trench‐parallel crustal‐scale thrust system (Misis–Kyrenia Thrust System) dissects the southern margin of the overriding plate and forms the structural grain and surface expression of northern Cyprus. Late Eocene to Miocene flysch of the Kythrea (Değirmenlik) Group is exposed throughout northern Cyprus, both at the hanging‐wall and foot‐wall of the thrust system, permitting access to an extensive Cenozoic sedimentary record of the basin. We report the results of a combined examination of detrital zircon and rutile U–Pb geochronology (572 concordant ages), coupled with Th/U ratios, Hf isotopic data, and quantitative assessment of grain morphology of detrital zircon from four formations (5 samples) from the Kythrea flysch. These data provide a line of independent evidence for the existence of two different sediment transportation systems that discharged detritus into the basin between the late Eocene and late Miocene. Unique characteristics of each transport system are defined and a sediment unmixing calculation is demonstrated and explained. The first system transported almost exclusively North Gondwana‐type, Precambrian‐aged detrital zircon sourced from siliciclastic rock units in southern Anatolia. A different drainage system is revealed by the middle to late Miocene flysch sequence that is dominated by Late Cretaceous – Cenozoic‐aged detrital zircon, whose age range is consistent with the magmatic episodicity of south‐east Anatolia, along the Arabia‐Eurasia suture zone. Deposition of these late Miocene strata took place thereupon closure of the Tethyan Seaway and African‐Eurasian faunal exchange, and overlap in time with a pronounced uplift of eastern Anatolia. Our analytical data indicate the onset of prominent suture‐parallel sediment transport from the collision zone of southeastern Anatolia into the Kyrenia Range of northern Cyprus, marking the drainage response to the continental collision between Arabia and Eurasia.

Neotethyan Subduction Ignited the Iran Arc and Backarc Differently

Article

Full-text available

May 2020

Most arcs show systematic temporal and spatial variations in magmatism with clear shifts in igneous rock compositions between those of the magmatic front (MF) and those in the backarc (BA). It is unclear if similar magmatic polarity is seen for extensional continental arcs. Herein, we use geochemical and isotopic characteristics coupled with zircon U‐Pb geochronology to identify the different magmatic style of the Iran convergent margin, an extensional system that evolved over 100 Myr. Our new and compiled U‐Pb ages indicate that major magmatic episodes for the NE Iran BA occurred at 110–80, 75–50, 50–35, 35–20, and 15–10 Ma. In contrast to NE Iran BA magmatic episodes, compiled data from MF display two main magmatic episodes at 95–75 and 55–5 Ma, indicating more continuous magmatism for the MF than for the BA. We show that Paleogene Iran serves as a useful example of a continental arc under extension. Our data also suggest that there is not a clear relationship between the subduction velocity of Neotethyan Ocean beneath Iran and magmatic activity in Iran. Our results imply that the isotopic compositions of Iran BA igneous rocks do not directly correspond to the changes in tectonic processes or geodynamics, but other parameters such as the composition of lithosphere and melt source(s) should be considered. In addition, changes in subduction zone dynamics and contractional versus extensional tectonic regimes influenced the composition of MF and BA magmatic rocks. These controls diminished the geochemical and isotopic variations between the magmatic front and backarc.

Origin and provenance of 2 Ma–2 Ga zircons ejected by phreatomagmatic eruptions of Pliocene basalts in southern Slovakia

Article

Oct 2019

U–Pb ages of zircons recovered from Pliocene pyroclastic deposits in northern part of the Cenozoic intra-Carpathian back-arc basin (Pannonian Basin) span the interval from Pliocene (2.2 Ma) to Paleoproterozoic (Orosirian–Rhyacian, 1850–2115 Ma). The scattered U–Pb ages reflect eruption ages of the host basaltic volcanic centres, two episodes of post-Eocene magmatic crustal growth, and the possible tectonic affiliation, provenance and age of the subjacent basement or the sedimentary basin detritus sampled by the basaltic magma. The youngest zircons define the maximum ages of phreatomagmatic eruptions during the Late Miocene–Pliocene extension. These zircons are distinguished from older zircons by Zr/Hf (40–90) and Th/U ratios (0.5–4.5) as well as super-chondritic εHf(t) values ranging from + 7 to + 14, indicating mantle-derived parental magmas. The locally increased Th/U ratios (up to 8) accompanied by Zr/Hf > 60 are diagnostic of evolved phonolite parental melt. Hence, the youngest zircons can be interpreted as antecrysts, originating from evolved melts cogenetic with the host alkali basalts. In contrast, older zircons represent xenocrysts scavenged by the uprising basalt from surrounding rocks. Subordinate Eocene–Early Oligocene (29–38 Ma) sub-group of zircon xenocrysts is coincidental with the magmatism and volcanism along the Periadriatic lineament and the middle-Hungarian zone. The Early Miocene (18 Ma) cluster is coeval with the deposition of the Bükk Mountains felsic ignimbrite correlated with the onset of the back-arc extension that triggered Miocene sedimentation within the Pannonian Basin. The Eocene–Early Oligocene zircons have been likely scavenged from pyroclastic and ash-fall deposits of the Palaeogene retroarc basin subjacent to the Miocene basin infilling. Sub-chondritic εHf(t) values between − 2.5 and − 8 in the Eocene–Early Miocene zircons attest their crystallization from subduction-related felsic-to-intermediate melts containing large amounts of recycled crustal material. Palaeozoic–Proterozoic zircons create a heterogeneous population with variable trace element abundances and εHf(t) values. The determined age clusters are reminiscent of some basement units cropping out recently in Central Western Carpathians. Zircon Hf isotope data indicate recycling of up to 3.4 Ga old mafic crust and also the presence of 2 Ga old juvenile mafic crust. These units had either underlain the northern part of the Pannonian Basin during Pliocene or had been exposed during the deposition of Miocene clastic sediments. The absence of Mesoproterozoic, Grenvillian zircons (0.9–1.8 Ga) in the pre-Cenozoic population of zircon xenocrysts is provisionally interpreted as indicating the evolution of the zircon source area within the west-African Craton.

Geochemistry of the Monte Filau orthogneiss (SW Sardinia, Italy): Insight into the geodynamic setting of Ordovician felsic magmatism in the N/NE Gondwana margin

Article

Full-text available

Feb 2019

The Mt. Filau orthogneiss is an Ordovician orthogneiss outcropping in the External zone of SW Sardinia chain. It consists of dark, biotite-rich facies, a leucocratic coarse-grained facies and a leucocratic fine-grained facies with igneous andalusite. Coarse- and fine-grained leucocratic orthogneiss have comparable major element contents, being slightly enriched in SiO2 and depleted in Fe2O3, MgO, TiO2 and CaO as compared to the biotite-bearing orthogneiss. Bt-bearing orthogneiss shows higher Sr and Ba concentrations than leucocratic ones, whereas Rb content is higher in leucocratic orthogneiss as compared to the Bt-bearing ones. Zr content shows a progressive decrease from biotite-bearing orthogneiss, coarse-grained leucocratic ones, to fine-grained orthogneiss. In the spider diagram the Mt. Filau orthogneiss shows the typical signature of calc-alkaline rocks, with negative anomalies of Ba, Nb, Sr and Ti, and positive anomalies in U, K. REE patterns of Bt-bearing and coarse-grained leucocratic orthogneisses are characterized by a moderate LREE fractionation, flat HREE and negative Eu anomaly. Fine-grained leucocratic orthogneiss shows flatter patterns, stronger Eu anomalies and slight HREE enrichment. The geochemical features suggest a clear evolution trend, from the less evolved Bt-bearing orthogneiss to the more differentiated fine-grained leucocratic orthogneisses which likely represent aplite bodies deriving from the most acidic residual melt. Selected trace and REE elements of Mt. Filau are compared with other Ordovician orthogneiss outcropping in the Axial zone of Sardinia Variscan belt. Besides, their geochemical features are also compared with metavolcanics of External and Nappe zone. The geochemical affinity of orthogneisses and metavolcanics from Variscan Sardinia, together with the geochronological data, allows to state a clear cogenetic relationship between the bodies belonging to the calc-alkaline Ordovician magmatic cycle. Our results suggest that the early Paleozoic basement of Sardinia might represents the witness of an early Paleozoic subduction-accretionary complex recording convergence along the N/NE Gondwana margin.

New Detrital Zircon Geochronology From the Cycladic Basement (Greece): Implications for the Paleozoic Accretion of Peri-Gondwanan Terranes to Laurussia

Article

Nov 2018

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.

Clastic wedge provenance in the Zemplinicum Carboniferous–Permian rocks using the U–Pb zircon age dating (Western Carpathians, Slovakia)

Article

Full-text available

Aug 2018

U–Pb (SHRIMP) detrital zircon ages from the Pennsylvanian–Permian meta-sedimentary rocks of the Zemplinicum Unit were used to characterise the provenance and the tectono-thermal evolution of the basement. The magmatic zircon ages from the contemporaneous rhyolite pyroclastics, ranging from 308 to 305 Ma, dated the Pennsylvanian sedimentary formations to the Moscovian and Kasimovian Ages. Two brakes in sedimentation within the Pennsylvanian–Permian sequence are presumed, first, flanked by Gzhelian–Asselian and second, intra-Permian. The detrital zircon age spectrum demonstrates two prominent populations: (i) Middle/Late Ordovician (age peak 459 Ma), (ii) Ediacaran–Cryogenian (age peaks 592 and 641 Ma). These, together with minor clusters from ~ 773 to 950 Ma, evidently document the Pan-African multiple magmatic events. The 1.1–1.8 Ga age gap and isolated zircons of Mesoproterozoic ages (1036–1361 Ma) are characteristic. Two populations, 1.8–2.2 Ga and 2.5–2.8 Ga, are presented within the Paleoproterozoic–Neoarchean zircons. The Zemplinicum Neoproterozoic arc crust had been affected by the extensional thermal relaxation and melting during Middle/Late Ordovician. The subsequent reworking had been connected with the Mississippian collision, followed by the Pennsylvanian/Permian extension. The presence of the Neoproterozoic detrital zircon ages including the Tonian ones permit to compare the Zemplinicum basement with the eastern peri-Gondwanan domain, which was situated at the northern margin of the Saharan Metacraton or the Arabian Nubian Shield during Neoproterozoic time.

Pre-Alpine evolution of the Seckau Complex (Austroalpine basement / Eastern Alps): Constraints from in-situ LA-ICP-MS U-Pb zircon geochronology

Article

Dec 2017
LITHOS

The Variscan European Belt is a complex orogen with its southern margin partly obscured by Alpine tectonics and metamorphism. We present a study of one of the units, the Seckau Complex, that constitute the southern part of the Variscan European Belt in the Eastern Alps in order to clarify its origin, age and lithostratigraphy. The magmatic and geochronological evolution of this Complex in the northwestern part of the Seckau Nappe (as part of the Austroalpine Silvretta-Seckau Nappe System) was investigated by zircon U–Pb dating of paragneisses and metagranitoids coupled with petrological and geochemical data. This reveals the distinction of three newly defined lithostratigraphic/lithodemic sub-units: (1) Glaneck Metamorphic Suite, (2) Hochreichart Plutonic Suite and (3) Hintertal Plutonic Suite. The Glaneck Metamorphic Suite is mainly composed of fine-grained paragneisses that yield U–Pb zircon ages in the range between 2.7 Ga and 2.0 Ga, as well as concordia ages from 572 ± 7 Ma to 559 ± 11 Ma. All of these ages are interpreted as detrital zircon ages originating from an igneous source. The paragneisses are the host rock for the large volumes of metagranitoids of the Hochreichart Plutonic Suite and the Hintertal Plutonic Suite. The Hochreichart Plutonic Suite comprises highly fractionated melts with mainly S-type characteristics and late Cambrian to Early Ordovician U–Pb zircon ages (508 ± 9 Ma to 486 ± 9 Ma), interpreted as magmatic protolith ages. The Hintertal Plutonic Suite is composed of metagranitoids with Late Devonian to early Carboniferous (365 ± 11 Ma and 331 ± 10 Ma) protolith ages, that intruded during an early phase of the Variscan tectonometamorphic event. The metagranitoids of the Hintertal Plutonic Suites define a magmatic fractionation trend, seen in variable Rb/Sr ratios. On this base they can be further subdivided into (a) the Griessstein Pluton characterized by S-type metagranitoids and (b) the Pletzen Pluton distinguished by intermediate to acidic metagranitoids with I-type affinity. The detrital zircon age spectra suggest a Neoproterozoic ancestry of the Glaneck Metamorphic Suite, which was located west of the Arabian Nubian Shield, probably next to the Trans-Saharan Belt. The early Paleozoic evolution of the recent Seckau Complex shows similarities to basement units of the Southalpine Unit, parts of the Austroalpine Unit and the Tatric and Veporic units of the Central Western Carpathians.

Zircon U‐Pb‐He Double Dating of Modern Sands From the Inn River Catchment: Assessing Resolution and Potential in a Complex Orogenic Setting

Article

Full-text available

Jan 2024

Zircon U‐Pb‐He double dating (ZDD) provides the opportunity to derive high temperature crystallization ages and low temperature cooling ages from the very same mineral grain, making it especially attractive for zircon provenance studies. We present the combination of in situ detrital zircon U‐Pb‐He double dating and Raman spectroscopy‐based heavy mineral analysis on different tributaries of the Inn river system applying a new grain embedding technique. The Inn river catchment drains a well‐studied complex nappe pile of the Eastern Alps exposing Austroalpine and Penninic crystalline basement rocks. Igneous formations of different emplacement ages, as well as various metasedimentary units, have experienced Alpine and diverse pre‐Alpine metamorphic overprints. This makes the area ideally suited for testing the sensitivity and potential of ZDD for fingerprinting various lithologically contrasting units with contrasting thermal histories. Results demonstrate that both high‐ and low‐temperature age distributions reflect the major sources and thermotectonic pulses, respectively. More specifically, the rocks of the Tauern Window with Miocene (U‐Th)/He ages as well as the Permian metagranitoids from the Tauern and the Err‐Bernina nappe in the uppermost Inn valley are recorded in the downstream Inn sample. The main mass of zircons in the lower Inn, however, derives from the Ötztal and Silvretta crystalline basement rock with Cadomian U‐Pb and Cretaceous (U‐Th)/He ages. The abundance of heavy minerals derived from metamafic formations shows no correlation to the area of such lithologies on the catchments and the different zircon fertility resulted in the overrepresentation of zircon U‐Pb ages from the Variscan igneous suites.

New Insıght ınto a Subductıon-Related Orogen: A Reappraısal of theGeotectonıc Framework and Evolutıonof the Middle and West Parts of the Southeast Anatolıan Orogenıc BELT (Türkiye)

Article

Full-text available

Aug 2023

The geotectonic framework and the evolutionary history of the Southeast Anatolian Orogenic Belt are closely related to the assemblage of eastern and western Gondwana and the subsequent events from the opening of the southern branch of the Neo-Tethys to the final collision. The first geotectonic event is the subduction of the Proto-Tethys under the northern Gondwana during the Ediacaran and accordingly the formation of igneous rocks within the lower units of Bitlis-Pütürge Massifs. The first orogeny affecting the region was the Cadomian orogeny. The southern branch of the Neo-Tethys began to open between the Arabian Plate (North of Gondwana) and today's southeastern Anatolian metamorphic massifs in the Late Triassic, and oceanic spreading continued 120 until the Late Cretaceous. The ophiolites and an intra-oceanic arc were formed during the Late Cretaceous (92 to 82Ma and 84-72 Ma respectively) in a SSZ tectonic environment formed by the northward subducting South Branch of Neo-Tethys ocean crust. The Arabian Platform entered the subduction zone and as a result ophiolites thrust on the Arabian Plate margin, the metamorphic massifs were fragmented and migrated to the South onto the ophiolites and arc magmatics in the Maastrichtian. Despite the collision, the continental subduction continued and a break-off of subducted slab was formed. A widespread marine transgression is realized onto the Arabian Platform and ophiolites from Latest Cretaceous to Early Miocene to the South of the Bitlis-Pütürge metamorphics. The remnant of the ocean continued untill Late Miocene to the North of the Bitlis-Pütürge massifs as marine basins with different depths and morphological characteristics. The magma formed by the partial melting of the mantle wedge, the rising deep asthenosphere mantle and the continental crust forms Maden arc over the ophiolites and the Bitlis-Pütürge Massifs in the Middle Eocene. Behind the Maden arc, shallow-deep marine carbonates and clastics were deposited in a back-arc basin (Kırkgeçit basin). The closure which started in the Late Eocene and ended in the Late Miocene enabled Southeast Anatolian Orogenic Belt to take its actual position.

Article no.AJOGER.103681 Bingöl and Beyarslan

Article

Aug 2023

Metabasic rocks from the Zemplinic crystalline basement (Western Carpathians, Slovakia): Metamorphic evolution and igneous protolith

Article

Full-text available

Dec 2022
GEOL CARPATH

Silurian anorogenic basic and acidic magmatism in Northwest Turkey: Implications for the opening of the Paleo-Tethys

Article

Nov 2019

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sarıcakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sarıcakaya Massif over an area of ca. 12 km by 1.5 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 ± 6 to 434 ± 7 Ma (2σ), and on those from a felsic vein an age of 319 ± 5 Ma (2σ) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial εHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of −16 to −9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the Paleo-Tethyan accretionary complexes, and (ii) the resemblance of the U\ \Pb age spectra of detrital zircons in the metaclastic sequence of the Sarıcakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the Anatolide-Tauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sarıcakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions.

Permian-Triassic granites of the Schladming Complex (Austroalpine basement): Implications for subduction of the Paleo-Tethys Ocean in the Eastern Alps

Article

Full-text available

May 2022
GONDWANA RES

Permian magmatic activity is widespread in the Austroalpine Unit stretching from Eastern Alps to the Western Carpathians and Pannonian region, the link between magmatism and the subduction of Paleo-Tethys Ocean is not well constrained up to now. Here, we report, for the first time, a Middle Triassic granite in the Austroalpine basement, which is at odds with a common opinion of the passive margin setting of this unit. The Tweng and Schladming Complexes representing a Neoproterozoic to Early Paleozoic magmatic arc were intruded by Permian and Triassic granites, related to back-arc extension triggered by the subduction of Paleo-Tethys Ocean. To reveal the tectonic affinity of these granitic rocks, we systematically analyzed their zircon geochronology and whole-rock geochemistry. The zircon U-Pb data show that the Tweng granitic gneisses and leucogranites were formed at 261 Ma and 244 Ma, respectively. The Schladming granitic gneisses were formed at 244 – 241 Ma, their εHf(t) values (-0.9 to +5.6) indicate their derivation from the lower crust and involved continent material. Geochemically, the granitic rocks from the Tweng Complexes have common features with subduction-related continental arc andesitic affinity. The granitic gneisses of Tweng and Schladming Complexes show A-type granite-affinity with high zircon crystallization temperatures of 784 – 835 ℃ and 781 – 818 ℃, respectively, whereas the Tweng leucogranites exhibit I-type granite characteristics and low zircon crystallization temperatures of 720 – 724 ℃. The geochemical features suggest that the Tweng granitic gneisses and leucogranites originated from the lower crust, while the Tweng leucogranites are explained by remelting of Tweng granitic gneisses, and interacted with subduction-related fluids. Therefore, we propose that the Permian-Triassic granitic rocks of Tweng and Schladming Complexes were formed in a back-arc setting during the subduction of the Paleo-Tethys Ocean, which finally resulted in the opening of the Meliata oceanic back-arc basin during Middle Triassic times.

First evidence for the subduction initiation and boninitic magmatism from the Armutlu Peninsula (NW Turkey): geodynamic significance for the Cadomian magmatic arc system of the Gondwanan margin

Article

Full-text available

Oct 2021
INT GEOL REV

The Cadomian Orogeny was active along the northern margin of Gondwanaland during the Late Neoproterozoic–Early Cambrian period. Remains of this orogenic activity are traced from Western Europe to the Himalayas, including some metamorphic basement rocks of Turkey. In this study, we provide new whole-rock and mineral chemistry, and zircon U–Pb age data for the metagabbro and metagranites in the Armutlu Peninsula, north of the Intra Pontide suture zone (IPSZ), which are the equivalent of the Cadomian basement of the İstanbul Zone (İZ). Geochemically, the metagabbros show an extreme depletion in Nb, Zr, Th, and Hf; low TiO2 contents; and high Mg# values exhibiting boninitic affinity, which are commonly associated with fore-arc settings. The metagranites are calc-alkaline and high-K calc-alkaline in character. They are slightly enriched in LREE and have similar features to shear-type plagiogranites. The yielded zircon U-Pb crystallization ages are 564 ± 4.4 Ma for metagabbros and 561 ± 9.5 Ma (Late Ediacaran) for metagranites. In this study, we provide additional information for the Cadomian basement of the İZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products.

Article

Full-text available

Mar 2021

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.

Tectonic evolution of Proto- and Paleo-Tethyan in the East Alps

Article

Full-text available

Jan 2020

Tethyan geodynamics

Article

Jan 2020

Tectonic Exhumation of the Central Alps Recorded by Detrital Zircon in the Molasse Basin, Switzerland

Preprint

Full-text available

Apr 2020

Abstract. Eocene to Miocene sedimentary strata of the Northern Alpine Molasse Basin in Switzerland are well studied, yet they lack robust geochronologic and geochemical analysis of detrital zircon for provenance tracing purposes. Here, we present detrital zircon U-Pb ages coupled with rare earth and trace element geochemistry (petrochronology) to provide insights into the sedimentary provenance and to elucidate the tectonic activity of the central Alpine Orogen from the late Eocene to mid Miocene. Between 35–22.5 ± 1 Ma, the detrital zircon U-Pb age signatures were dominated by age groups of 300–370 Ma, 370–490 Ma, and 490–710 Ma, with minor Proterozoic age contributions. In contrast, from 21.5 ± 1 Ma to ~ 13.5 Ma (youngest preserved sediments), the detrital zircon U-Pb age signatures were dominated by a 252–300 Ma age group, with a secondary abundance of the 370–490 Ma age group, and only minor contributions of the 490–710 Ma age group. The Eo-Oligocene provenance signatures are consistent with interpretations that initial basin deposition primarily recorded exhumation and erosion of the Austroalpine orogenic cover and minor contributions from underlying Penninic units, containing reworked detritus from Variscan, Caledonian, and Cadomian orogenic cycles. The dominant 252–300 age group from the younger Miocene deposits is associated with the exhumation of Variscan-aged crystalline rocks of upper-Penninic basement units. Noticeable is the lack of Alpine-aged detrital zircon in all samples with the exception of one late Eocene sample, which reflects Alpine volcanism associated with incipient continent-continent collision. In addition, the rare earth and trace element data from the detrital zircon, coupled with zircon morphology and U/Th ratios, point to primarily igneous and rare metamorphic sources of zircon. The observed change in detrital input from Austroalpine to Penninic provenance in the Molasse Basin at ~ 22 Ma appears to be correlated with the onset of synorogenic extension of the Central Alps. Synorogenic extension accommodated by slip along the Simplon fault zone promoted updoming and exhumation the Penninic crystalline core of the Alpine Orogen. The lack of Alpine detrital zircon U-Pb ages in all Oligo-Miocene strata also shows that the Molasse Basin drainage network was not accessing the prominent Alpine age intrusions and metamorphic complexes located in the southern portion of the Central Alps.

Silurian anorogenic basic and acidic magmatism in Northwest Turkey: Implications for the opening of the Paleo-Tethys

Article

Nov 2019
LITHOS

The Sakarya Zone (northern Turkey) is a Gondwana-derived continental block accreted to northern Laurussia during the Carboniferous, and is regarded as the eastward extension of Armorica. Timing of its detachment from the northern margin of Gondwana, thus opening of the Paleo-Tethys, is poorly known. Here, we report on metagranite and amphibolite with Silurian igneous crystallization ages from the Early Carboniferous high-temperature/middle to low-pressure amphibolite-facies metamorphic rocks of the Sarıcakaya Massif within the Sakarya Zone (NW Turkey). The metagranite-amphibolite complex is exposed mainly along the southern margin of the Sarıcakaya Massif over an area of ca. 12 km by 1.5 km. The metagranite contains preserved domains of porphyric texture, indicative of derivation from a former granite porphyry. The amphibolite is devoid of any relict igneous texture. Both the metagranite and amphibolite are crosscut by late up to 50 cm thick felsic veins. Uranium-Pb dating on igneous zircons from both metagranite and amphibolite yielded Silurian ages of ca. 419 ± 6 to 434 ± 7 Ma (2σ), and on those from a felsic vein an age of 319 ± 5 Ma (2σ) (Late Carboniferous). Geochemically, amphibolite displays anorogenic transitional tholeiitic to alkaline signatures. Initial εHf values of the igneous zircons from both metagranite and amphibolite show a large variation with medial values of −16 to −9 and + 3 to +6, respectively. Thus, the protoliths of amphibolite were derived from melts of depleted mantle, and those of the metagranite, on the other hand, from melts of reworked crustal material. We suggest that the Silurian anorogenic magmatism is related to a rifting event at the northern margin of Gondwana leading to the detachment of the Sakarya Zone and hence placing an age on the initial opening of the Paleo-Tethys. This interpretation is based on (i) the presence of Late Silurian to Devonian deep-sea sedimentary blocks in the Paleo-Tethyan accretionary complexes, and (ii) the resemblance of the UPb age spectra of detrital zircons in the metaclastic sequence of the Sarıcakaya Massif to those of Cambro-Ordovician sandstones in Jordan (Gondwana), and (iii) the local occurrence of anorogenic A-type granites of Late Ordovician-Silurian age in the Anatolide-Tauride Block, a continental block which rifted from Gondwana during the Early Triassic. Wholly anorogenic nature of the Late Ordovician to Silurian igneous rocks in the Sarıcakaya Massif and reported in literature does not support the opening of the Paleo-Tethys as back-arc ocean, as suggested in most paleogeographic reconstructions.

Variscan Cycle

Chapter

Aug 2019

J. F. Simancas

This chapter summarizes the classical and recent ideas together with the geodynamic hypotheses regarding the Variscan Cycle in Iberia, as an introduction to the more extensive presentations developed in the following chapters. Thus, the review focuses on the following issues: (i) uncertainties about the onset and end of the Variscan cycle; (ii) putative continents and terranes involved in the Variscan puzzle; (iii) main stages of the Variscan evolution in Iberia; (iv) deep crustal features of the Iberian Variscides; and (v) arc-shaped geometry. A brief reference to the particular problems of the Variscan basement in the Iberian Alpine orogens is also made. The attempt has been made to display a broad and rather eclectic state-of-the-art, though the author’s preferences have not been totally avoided.

Variscan orogeny in the Eastern Alps and Bohemian Massif: how do these units correlate?

Article

Full-text available

Jan 1999

A review of geochronological data from the Eastern Alps

Article

Full-text available

Jan 1999

Martin Thöni

Within both of the major tectonostratigraphic units of the Eastern Alps (the Penninic and the Austroalpine complexes) the oldest ages (U-Pb on zircon) have been determined from intermediate or mafic meta-igneous rocks that indicate crystallisation of various magmatic protoliths during the Latest Proterozoic (650-600 Ma). In the Austroalpines, intense magmatic activity is constrained by U-Pb, Sm-Nd and Rb-Sr ages for the time span of 610-420 Ma. The magmas were emplaced into metasediments with a Middle Proterozoic (c. 1.6 Ga) mean crustal residence age. These Late Proterozoic-Early Palaeozoic rock-forming processes are related to rifting, as well as collisional-orogenic events. The "Zentralgneise" of the Hohe Tauern represent Carboniferous intrusions (336-308 Ma). The medium- to high-grade mineral parageneses and correlated structures of major parts of the Austroalpine " Altkristallin " (e.g. Ulten, Otztal, Schladming subunits) are also Variscan in age. An early, c. 350 (+/- 10) Ma old HP event is preserved in metabasites of the central Otztal area. In the same basement unit, the thermal peak in Grt - St - Ky +/- Sil +/- And gneisses was reached at 330 +/- 10 Ma. Regional cooling (below 500 degrees C) began at about 310 (+/- 10) Ma. Permo-Triassic rift-related events were recently confirmed by ages from various igneous assemblages (c. 290-240 Ma). This magmatic activity is related to extensional processes, mantle upwelling and initial rifting in the southeastern Austroalpine realm, which was probably accompanied by a metamorphism of low-P type (andalusite) in the continental crust. Alpine subduction, metamorphism and deformation of the basement probably commenced during the Jurassic and culminated in the internal Austroalpines during Middle Late Cretaceous times (c. 100 +/- 10 Ma), with peak PT conditions of 20 kbar and 600-700 degrees C, followed by rapid, near-isothermal decompression and exhumation, nappe thrusting and cooling (90-65 Ma). Following Austroalpine nappe imbrication and NW-directed thrusting, subduction of the southern Penninics below the Austroalpines reaches eclogite facies conditions during NS compression, at 20 kbar / 600 degrees C. However, a Late Cretaceous vs Eocene age for this subduction-related high-P metamorphism is still under discussion. Maximum temperatures in deeper tectonic levels of the Tauern window were attained during the late stages of Penninic nappe imbrication and continental collision, i.e. during exhumation, some 30 +/- 5 Ma ago. Mica cooling and apatite fission track ages in these areas are in the range of 30-15 and 10-5 Ma, respectively. In the Austroalpines, the post-Cretaceous metamorphic imprint is only local and weak. Cooling below 300 degrees C was mostly accomplished by Paleocene limes. Tertiary (mainly Oligocene) intrusions and dykes are almost unaffected by metamorphism.

New data on the age of deposition of the South-Alpine phyllitic basement in the Eastern Alps

Article

Full-text available

Dec 1984
Neues Jahrbuch Geol Palaontol Monatsh

Lower Ordovician migmatisation in the Ötztal crystalline basement (Eastern Alps, Austria): Linking U-Pb and Pb-Pb dating with zircon morphology

Article

Full-text available

Jan 1997

Partial anatexis of bio-plag-paragneisses is known from several sites within the Ötztal crystalline complex, a polymetamorphic basement unit of the Eastern Alps in Austria. One of these migmatite areas, the "Winnebach"-migmatite, has been investigated by single zircon Pb-Pb evaporation and conventional U-Pb zircon analysis in order to establish the time of the migmatisation. To be able to distinguish the anatectic event from other pre-Variscan metamorphic events, the zircon populations of the migmatite were compared to those of the adjacent paragneisses. Except for one zircon type, all populations exhibit polyphase crystal growth and do not show any specific mode of occurrence. Measured by single grain evaporation these zircon populations document three metamorphic events with mean 207Pb/206Pb ages of 484 ± 6 Ma, ∼ 560 Ma, and ∼ 635 Ma. However, since these ages are found both within the migmatite and the paragneiss, none of them can be directly assigned to the migmatisation. One population of spheroidal, clear and colourless specimens is found to be characteristic for the migmatite only. These anatectically grown zircons yield a concordant U-Pb age of 490 ± 9 Ma, thus proving the Early Ordovician event to have caused the anatexis. The minimum age of some of the inherited zircon cores can be established around 2440 Ma using both methods, thus providing evidence for the assimilation of zircons derived from earliest Proterozoic and/or Archaean sources.

The making and becoming of Apulia

Article

Full-text available

Jan 1999

Alpine metamorphism in the Eastern Alps

Article

Full-text available

Jan 1999

The metamorphic overprint of the Eastern Alps during Alpine times shows significant differences between the two main tectonic units, the Penninic and the Austroalpine, in terms of pressure, temperature, time and tectonic evolution. The Penninic units are characterized by mainly oceanic rocks and fragments of continental polymetamorphic basement and metasedimentary cover which underwent high-pressure metamorphism of low geothermal gradients between c. 7-13 °C/km typical for a subduction zone. This metamorphism caused eclogite formation at maximum crustal depths of about 70 to 85 km (18 to 25 kbar at 600 °C) which is restricted to the Tauern Window and subsequently the formation of blueschists at 10 to 15 kbar and 400 to 450 °C in the Tauern Window and 6 to 8 kbar at ~ 350 °C in the Engadine and Rechnitz Windows. The dominant rock-forming mineral assemblages however are due to a subsequent greenschist to amphibolite facies overprint. In the Engadine and Rechnitz Window only lower greenschist facies conditions of ~ 350-450 °C at ~ 2-4 kbar are recorded whereas in the Tauern Window a concentric metamorphic zonation reaching a maximum of 7 kbar at ~ 550-600 °C in the centre is observed. For the Tauern Window the geothermobarometric results indicate a discontinuous two-stage PT-loop. The age of this metamorphic evolution of the Penninic realm is well known for the late greenschist to amphibolite facies event which took place shortly after 30 Ma and is recorded by cooling ages and fission track studies. The exact age of the high-pressure event is still unknown. The oldest calculated age for the onset of Alpine metamorphism in the Tauern Window however is 62 Ma (Christensen et al., 1994) which is older than the proposed age of eclogite formation in the Central Alps reported by Gebauer et al. (1992) but coincides with Eocene Ar/Ar-ages reported by Zimmermann et al. (1994) for the Tauern Window. The Lower Austroalpine unit, the paleogeographic link between the Penninic units and the Austroalpine continental plate shows a metamorphic evolution similar to that of the Penninic realm. In the Lower Austroalpine units adjacent to the western Tauern Window a high-pressure event in the range of ~ 10 kbar and ~ 350 °C was overprinted by greenschist facies conditions of ~ 4 kbar and 400 °C during Eocene times, whereas east of the Tauern Window thorough PT-estimates are still missing. In the Lower Austroalpine units at the eastern end of the Alps a different metamorphic evolution is recorded with greenschist- to amphibolite facies conditions of 8-9 kbar and 500-550 °C, reflecting higher geothermal gradients than in the Penninic high-pressure event, and characterized by Cretaceous mineral ages of ≤ 80 Ma. Cretaceous ages have also been recorded for the Middle Austroalpine units that represent the polymetamorphic basement and sedimentary cover of the continental plate below which the Penninic units were subducted. The Alpine metamorphic overprint increases from north towards the south from lower greenschist to amphibolite facies. Locally preserved relic eclogite facies conditions of 12 kbar and 550 °C in the west (Otztal Alps) and 18-20 kbar and 700 °C in the east (Koralpe) represent geothermal gradients of around 20 °C/km. The subsequent amphibolite facies overprint is interpreted as due to uplift and exhumation after a collisional episode in a subduction regime. The reason for this could be a continent-continent collision at the western end of the Tethys in the late Cretaceous due to the closure of the Hallstatt-Meliatta ocean basin about 100-90 Ma in age, predating the sedimentation of the late Cretaceous Gosau group sediments. The Upper Austroalpine and Southalpine sediments of the Alpine sedimentation cycle starting in the late Carboniferous/Permian however are slightly effected by very low- to low-grade metamorphism with decreasing intensity from north to south, due to internal thrusting in the course of a collisional tectonic environment at the western end of the Tethys during Jurassic/Cretaceous times.

Cadomian magmatism in the Alps recorded in Late Ordovician sandstones of the Carnic Alps: Preliminary results from zircon Pb/Pb evaporation dating

Article

Full-text available

Jan 2001

207Pb/206Pb evaporation age dating of euhedral detrital zircons from the Late Ordovician Uggwa Formation, eastern Carnic Alps, yields two age groups, including (1) a group with a pooled age of 650 ± 24 Ma and (2) a bad constrained age group of 518 ± 76 to 533 ± 106 Ma. The younger age group is similar to acidic orthogneisses of the Austroalpine basement complex. The older ages coincide with 40 Ar/39 Ar ages of detrital white mica from the same stratigraphic level, and suggest together with mica ages, therefore, the presence of a Cadomian metamorphic/magmatic orogenic belt. We interpret the new zircon ages to record two stages of magmatism related to Late Cadomian tectonic events. Ages of inherited zircon cores include apparent minimum ages ranging from c. 2.0 Ga to c. 900 Ma displaying possible close paleogeographic relationships with Gondwanan and/or Baltic tectonic elements.

A Cambrian island arc in the Silvretta nappe: Constraints from geochemistry and geochronology

Article

Full-text available

Jan 1997

Mafic, intermediate and felsic polymetamorphic gneisses in the Austroalpine Silvretta nappe are traditionally called "Older Orthogneisses "; investigation of their geochemical and Nd isotopic characteristics as well as age determinations by the U-Pb zircon method revealed that this unit is heterogeneous in terms of origin, geodynamic setting and age. A dioritic protolith was emplaced in an arc-type setting 609 ± 3 Ma ago. A flasergabbro, a metagabbro with preserved magmatic textures and a melatonalite yielded U-Pb ages of 523 ± 3,522 ± 6 and 524 ± 5 Ma, respectively. They intruded into a basement consisting of metasediments typical for active continental margin deposits and interlayered with intrusive/extrusive metabasites from a T- to P-type MORB source, but, on the other hand, occur together with coeval ophiolitic rocks. Metagabbros and metatonalites are proposed to have been formed in an island arc, either in the vicinity of an active continental margin or in a back-arc setting. The heterogeneous rock suite was subsequently involved in orogenic processes during Ordovician times and again intruded by gabbroic melts 475 Ma ago. The studied rocks reveal the existence of an oceanic domain between Gondwana and Laurasia continental blocks prevailing over a period of more than 150 myr in the Late Proterozoic, Cambrian and Ordovician.

The Intra-Alpine terrain: A Paleotethyan remnant in the Alpine Variscides

Article

Full-text available

Jan 1996
Eclogae Geol Helv

Gérard Maurice Stampfli

A Cordilleran type evolution is proposed for the Variscan orogen of middle Europe. This orogenesis is regarded as mainly evolving through terrain accretion and subsequent collapse of the overthickened crust. A major terrain accretion took place between late Devonian and early Carboniferous when the Intra-Alpine terrain collided with the Ligerian-Moldanubian active margin. This terrain is regarded as being a segment of the northern margin of Paleotethys. Oblique subduction of Paleotethys under the newly accreted terrain is responsible for the voluminous calc-alkaline magmatism in late Carboniferous. The Paleotethys subduction has generated a lateral displacement of the eastern part of the Intra-Alpine terrain inducing a duplication of its western end. The late Carboniferous closure of Paleotethys in middle Europe is not found eastward where this closure happened only in early-Triassic times, following the simultaneous opening of the Neotethys ocean and the Meliata back-arc. Palinspastic models of the western Tethyan realm are proposed from the Carboniferous to early Jurassic.

Tectonothermal evolution of the internal Alps and Carpathians: Evidence from40Ar/39Ar mineral and whole-rock data

Article

Full-text available

Jan 1996
Eclogae Geol Helv

40Ar/39Ar dating within the internal Eastern Alps, Western Carpathians, Southern Carpathians, and Apuseni Mountains has been carried out in order to constrain and compare (1) ages of tectonothermal overprint within basement units; (2) the extent of Alpine metamorphic overprint on Permian to Mesozoic cover sequences and (3) the sequence of Alpine tectonothermal events. Stratigraphic controls suggest that all these sections were affected by Cretaceous ("early Alpine") orogenic events during Alpine evolution. Pre-Alpine tectonothermal events range from Early Cadomian to Late Variscan within the area considered. 40Ar/39Ar ages of detrital muscovite of Ordovician-Silurian sandstones within the Eastern Alps suggest a linkage to Cadomian sources (640-580 Ma). Comparison of geochronological data from pre-Alpine Austroalpine basement complexes within the Eastern Alps, the Western Carpathians and the Apuseni Mountains indicates that these represent units which have been affected by contrasting and/or diachronous tectonometamorphic events. As indicated by new mineral age data, their tectonothermal evolution ranges from Early (e.g., c. 420-380 Ma) to Late Variscan (330-300 Ma). By contrast, preliminary amphibole and muscovite data from various basement units within Southern Carpathians argue for uniform Late Variscan cooling after medium grade metamorphism. It appears that the Eastern Alps, Western Carpathians and Apuseni Mts. represent a composite of basement units with variables ages of accretion during early to late Paleozoic orogenic events along northern margins of Gondwana. The uniform Late Variscan cooling ages within Southern Carpathian basement units are interpreted to represent cooling within rift shoulders during ongoing extension and break-up within the future Tethys realm. This interpretation is confirmed by the presence of distinct mylonite zones within the Southern Carpathians and Eastern Alps where white mica ages suggest Early Permian tectonothermal activity with cooling and extension. Based on stratigraphic and 40Ar/39Ar mineral age control on mylonites and penetratively ductilely deformed cover and basement rocks we distinguish three major Alpine tectonic events: (1) blueschist facies metamorphism in the West Carpathian Meliata unit associated with subduction of oceanic crust during the Late Jurassic (40Ar/39Ar phengite ages: 150-160 Ma); (2) varying tectonothermal overprint during continent-continent collision during the Middle and early Late Cretaceous ("pre-Gosau" deformation event) between c. 120 Ma and c. 86 Ma. The age of deformation decreases from hangingwall to footwall units in all investigated sections. This event apparently includes an early short-lived eclogite facies metamorphism (only in the Alps) associated with A-subduction of continental crust (with amphibole cooling ages indicating subsequent exhumation and cooling between c. 136 and 108 Ma); (3) Late Cretaceous ("intra-Gosaouian") cooling and associated activity of detachment faulting in higher tectonic levels and contemporaneous low-temperature tectonic stacking in deeper structural levels between c. 86 Ma and 65 Ma. This feature is interpreted to represent extension in an overall contractional setting. Furthermore, there is no apparent thermal overprint within the Austroalpine nappe stack in connection with the piggy-back emplacement of the entire Cretaceous nappe complex onto the stable European foreland during Tertiary continent-continent collision.

High-pressure metamorphism of phengite gneisses in the Lower Austro-Alpine nappe unit, Eastern Alps: Mineral equilibria, P-T parameters, and age

Article

Full-text available

Nov 1998

Mineral assemblages and the composition of minerals were studied in ortho- and paragneisses of the Lower Austro-Alpine Unit (Wechsel and Grobgneis complexes) and the overlying Permian-Triassic metasandstone in the Eastern Alps. The mineral assemblages of these rocks and the compositions of minerals coexisting in them (muscovite-phengite, chlorite, garnet, biotite, tourmaline, albite, and potassium feldspar) are similar and point to metamorphic conditions of the garnet subfacies of the greenschist facies with the Grt + Chl + Phn + Qtz critical assemblage, T = 470-500"C (Grt-Chl and Grt-Bt thermorneters), P - 10 kbar (Phn-Bt-Kfs-Qlz barometer). The fact that the zoning of the garnet and tourmaline is always prograde and the rocks bear no higher temperature minerals points to the prograde character of metamorphism. This is at variance with preexisting concepts of the retrograde character of metamorphism in the Wechsel and Grobgneis complexes and the occurrence of an older stage of amphibolite metamorphism in them. The U-Pb zircon age of the orthogneisses (metagranites) from the Wechsel Complex, which are metamorphosed to the same grade as the host rocks, indicates that the magmatic crystallization (protolith) age of the parent granite is approximately 603 Ma (Cadomian cycle), and the age of metamorphism under garnet subfacies conditions is 109 Ma (Early Alpine cycle). This explains the similar metamorphic parameters and mineral equilibria in rocks of the Wechsel and Grobgneis complexes and those of the Permian-Triassic cover. Given the general prograde character of the Early Alpine metamorphism, the temperature of the possible pre-Alpine (603 -109 Ma) metamorphic events in the Wechsel and Grobgneis complexes could not be higher than that of the garnet subfacies.

The evolution of pre-Variscan eclogites of the Tauern Window (Eastern Alps): A Sm/Nd-, conventional and Laser ICP-MS zircon U-Pb study

Article

Full-text available

Jan 1997

en): Quadt, Albrecht von / Günther, Detlef / Frischknecht, Rolf Objekttyp: Article Zeitschrift: Schweizerische mineralogische und petrographische Mitteilungen Band(Jahr): 77(1997) Heft 3 Persistenter Link: http://dx.doi.org/10.5169/seals-58484 Erstellt am: Dec 4, 2013 Nutzungsbedingungen Mit dem Zugriff auf den vorliegenden Inhalt gelten die Nutzungsbedingungen als akzeptiert. Die angebotenen Dokumente stehen für nicht-kommerzielle Zwecke in Lehre, Forschung und für die private Nutzung frei zur Verfügung. Einzelne Dateien oder Ausdrucke aus diesem Angebot können zusammen mit diesen Nutzungsbedingungen und unter deren Einhaltung weitergegeben werden. Die Speicherung von Teilen des elektronischen Angebots auf anderen Servern ist nur mit vorheriger schriftlicher Genehmigung möglich. Die Rechte für diese und andere Nutzungsarten der Inhalte liegen beim Herausgeber bzw. beim Verlag. Abstract Geochronological and geochemical analyses were carried out in order to charactenze the geological evolution of the pre-Vanscan basement of the Tauern Window (Eastern Alps) The Penninic units of the Lower Schist Cover from the central part of the Tauern Window host meta-basalts, ortho-and paragneisses and subordinate quartzites and graphite schists These units were intruded by several granitoid plutons in Variscan time A chronology and isotopic signatures for the Lower Schist Cover (LSC) evolution and magmatism was estab¬ lished dating various eclogitic amphibolites by conventional and laser ablation microprobe (LAM-ICP-MS) U-Pb zircon techniques and Sm-Nd mineral analyses Zircons of the eclogitic amphibolites yielded an age of 488 ± 12 Ma interpreted as the igneous protolith emplacement age similar to those from the northern part of the Lower Schist Cover Ages of 418 ± 18 Ma (U-Pb-zircon), 415 ± 18 Ma (LAM ICP-MS, zircon) and 422 ± 16 Ma (Sm-Nd) are the first evidence of a Silurian metamorphic overprint within the Eastern Alps The new LAM-ICP-MS technique results in concordant U/Pb zircon ages in contrast to the discordant conventional U/Pb zircon age Analysed zircons did not include an old lead component, an episodic Pb-loss of Variscan and Alpme age causes the discordance of the zircon fractions The high-pressure metamorphism converted these mafic rocks into eclogites during the Silurian subduc¬ tion Sm-Nd whole rock analyses define a reference line at 845 ± 26 Ma with an initial e-Nd value of +5 3 Such old protolith ages are known from other parts of the Alps, but in this case no geological significance is attributed to this age No old intrusion ages are detectable by U-Pb zircon techniques Thus, the e-Nd T-500 signatures along with dif¬ ferent REE pattern and trace element discrimination diagrams are interpreted to reflect a shghtly enriched mantle source A detailed Sm-Nd whole rock study within one eclogite body demonstrates that the Nd systematics were dis¬ turbed after the Cambrian intrusion and partly re-homogemzed during the Variscan and/or Alpine metamorphism

Oceanic vs Continental Origin of the Paleozoic Habach Formation in the Vicinity of the Felbertal Scheelite Deposit (Hohe Tauern, Austria) A geochemical Approach

Article

Full-text available

Ozeanische vs kontinentale Entstehung der paläozoischen Habach-Formation in der Nachbarschaft der Scheelitlagerstätte Felbertal (Hohe Tauern, Österreich) Eine geochemische Studie Zusammenfassung Die Habachformation des Unterfahrungsstollens der Scheelitlagerstätte Felbertal (Salzburg/Österreich) besteht aus verschiedenen Magmatiten und Sedimenten, die bei der alpinen Metamorphose in Grünschieferfazies bzw. in Amphibolitfazies umgeprägt wurden. Aufgrund des weitgehenden Fehlens urspünglicher Relikte basiert die vorliegende Studie vorwiegend auf geochemischen Untersuchungen. Zwei magmatische Abfolgen konnten unterschieden werden. Die tiefere, Untere Magmatitabfolge -sie besteht im wesentlichen aus feinkörnigen Amphiboliten und untergeordnet interme-diären Schiefern und Gneisen sowie aus Hornblenditen -wird als subvulkanischerTeil der ozeanischen Kruste eines "marginal basins" (sheeted dike) interpretiert, mit Intrusionen intermediärer und saurer Zusammensetzung, die aus einem kontinentalen Inselbogenmagmatismus herzuleiten sind. Authors' address: Ao. 79 Die vorwiegend vulkanogene Obere Magmatitabfolge, bestehend aus verschiedenen basischen bis sauren Metavulkaniten mit geringen Metasedi-mentzwischenlagen, kann als Produkt eines kontinentalen Inselbogens angesehen werden. Im Hangendbereich der Oberen Magmatitabfolge, der sogenannten Habachentwicklung, treten neben dominierenden Metasedimenten einzelne Amphibolite mit Intraplattencharakteristik auf. Folgendes Entwicklungsmodell wird vorgeschlagen: Im Bereich eines älteren Inselbogens kommt es zur Bildung eines "marginal basins" als dessen Teil die Untere Magmatitabfolge angesehen wird. Eine spätere Schließung des Beckens führt zu einer teilweisen Obduktion der ozeanischen Kruste und zu einem Zergleiten des Krustenpakets. Auf den "sheeted dike" Komplex der Unteren Magmatitabfolge werden in der Folge kalkalkalische (z.T. shoshonitische) Vulkanite des kontinentalen Inselbogens der Oberen Magmatitabfolge abgelagert. Gleichzeitig intrudieren kalkalkalische Schmelzen die Untere Magmatitabfolge. Das Ende der Subduktion führt einerseits zum Ausklingen des Vulkanismus, andererseits zur verstärkten Ablagerung von tonigen Sedimenten (Habachphyllitentwicklung) und zum Auftreten eines basischen Intraplattenvulkanismus. Abstract The Habach Formation exposed in the "Unterfahrungsstollen" of the Felbertal scheelite deposit (Salzburg/Austria) consists of several types of former magmatic and sedimentary rocks metamorphosed into greenschist to amphibolite facies during the Alpine orogeny. Due to the lack of primary features the following interpretation is based mainly on a geochemical investigation. Two different magmatic sequences can be distinguished. The Lower Magmatic Sequence (LMS) is essentially made up of fine-grained amphibolites. In addition, different types of intermediate to acidic schists and gneisses and, restricted to the basal sections, hornblendites occur. The LMS is interpreted as sheeted dike-complex originating from an oceanic marginal basin. However, the intermediate to acidic intercalations are considered to be intrusive and related to a continental island arc magmatism. The Upper Magmatic Sequence (UMS) with predominant metavolcaniclastic rocks intercalated by minor metasediments has been formed in a contin-ental island arc setting. On top of the UMS metasediments ("Habachphyllitentwicklung") prevail over metavolcanic rocks. Rare amphibolites indicate a final within-plate magmatism. The following geological model is proposed: A marginal basin is established in the area of an older island arc. The LMS is considered to be a remnant of this basin. Subsequent closure of the basin led to obduction and splitting up of the oceanic crust. Calc-alkalineto shoshonitic volcaniclastics (UMS) were deposited on the sheeted dike-complex (LMS). Contemporary calc-alkaline dikes feeding the UMS were found intruding the LMS. The decrease in island arc volcanism was associated with an increase in argillaceous sedimentation and with a basic within-plate magmatism.

Early Paleozoic Back-Arc and Island-Arc Settings in Greenstone Sequences of the Central Tauern Window (Eastern Alps)

Article

Full-text available

Jan 1987

Zusammenfassung Im zentralen Teil des Tauernfensters wurden Grünsteinfol-gen (hauptsächlich niedriggradige Amphibolite) petrographisch und geochemisch untersucht. Ihr vermutetes Alter, das in einem Fall auch radiometrisch belegt ist, ist frühpaläozoisch. Der Basisamphibolitkomplex enthält ultramafische Gesteine (z. B. Stubachtal) und metagabbroische und metabasaltische Amphibolite. Die alpidische Metamorphose hat bereichsweise vermutlich die Grenze zur Amphibolitfazies überschritten. Der geochemische Charakter der Metabasite wird einem Bildungs-milieu im Backarc-Bereich hinter einem Inselbogen zuge-schrieben. Es gibt auffallende Ähnlichkeiten zur Geotimes-Ein-heit in Oman. Der Weinbühel-und der Tauernkogelamphibolit, die beide der Habachformation angehören (der Tauernkogelamphibolit ist Teil der Riffldecke), zeigen mit ihren zoniert gebauten Pla-gioklasen und Amphibolen prograde Metamorphose bis in die höhere Grünschieferfazies an. Die Ausgangsgesteine waren hauptsächlich Andesite mit low-K-Charakter, doch gibt es auch Basalte und Dazite. Aufgrund ihrer geochemischen Zusam-mensetzung können die Gesteine als typische primitive Insel-bogenfolge klassifiziert werden. Stark deformierte und rekri-stallisierte Gesteine enthalten infolge passiver Anreicherung erhöhte Konzentrationen von immobilen Spurenelementen. Ihr sekundäres Spurenelementmuster ähnelt daher jenem al-kalischer Gesteine. Metasedimentgesteine sind großteils vul-kano-detritischen Ursprungs. .) Authors' addresses: Univ.-Prof. Dr. WOLFGANGFRISCH, Insti-tut für Geologie und Paläontologie, Universität Tübingen, Sig-wartstraße 10, 0-7400 Tübingen; DIETER RAAB, Institut für Ge-wässerschutz und Wassertechnologie der ETH, Überland-straße 133, CH-8600 Dübendorf. Die Amphibolite der Scheelitlagerstätte Felbertal gehören der Habachformation an (Fortsetzung des Weinbühelamphibo-lits), weisen aber geochemische Charakteristika auf, die an die Backarc-Sequenz des Basisamphibolits erinnern. Möglicher-weise repräsentieren sie ein Übergangsstadium zwischen der Bildung des Backarc-Beckens und des Inselbogens der Hab-achformation, die auf der Backarc-Kruste aufsetzt. Die Amphibolitfolgen werden von variszischen Granitoiden intrudiert oder tektonisch unterlagert, die durch die alpidische Gebirgsbildung zu den meist längsgestreckten Zentralgneis-körpern umgeformt wurden. Die Situation erinnert an archai-sche Granit-Grünstein-Gürtel, für deren Bildung verschiedent-tlich ein Backarc-Milieu gefordert wurde. Summary In the central part of the Tauern Window, greenstone se-quences (mainly low grade amphibolites) of an inferred and, in one case, proven, early Paleozic age were investigated petro-graphically and geochemically. The Basis Amphibolite Complex contains ultramafic rocks (Stubachtal Body) and metagabbroic and metabasaltic am-phibolites. Alpine metamorphism is suggested to have reached the medium-grade level in places. The geochemical character of the metabasic rocks is interpreted in terms of a back-arc geotectonic setting behind an island arc. There are striking similarities to the Geotimes unit in Oman. The Weinbühel and Tauernkogel Amphibolites, which belong to the Habach Formation (the Tauernkogel Amphibolite is part of the Riffl Nappe), show prograde metamorphism up to the upper greenschist facies on the base of zonation of plagio-clase and amphibole. The source rocks are mainly andesites of low-K character but there are also basalts and dacites. From their geochemistry the rocks can be classified as a typi-cal primitve island arc sequence. Strongly deformed and re-545 crystallised rocks contain elevated levels of immobile trace elements due to passive enrichment. They therefore attained a secondary trace element pattern similar to that of alkaline rocks. Metasedimentary rocks are mainly of volcano-detrital origin. The amphibolites of the Felbertal scheelite mine belong to the Habach Formation (continuation of the Weinbühel Am-phibolite) but show a geochemical pattern reminiscent of the back-arc sequence of the Basis Amphibolite. They possibly represent a transitional stage between the formation of the back-arc basin and the island arc of the Habach Formation which formed on top of the back-arc crust. Variscan granitoids are found as intrusions in the amphibo-lite sequence or underlie the sequences with tectonic contacts. These granitoids were altered to the generally elongate Zen-tralgneis bodies during Alpidic times. The overall situation re-sembles Archaean granite-greenstone belts, for which a back-arc setting has been proposed by several authors.

The Phanerozoic Time Scale

Article

Full-text available

Mar 1996
EPISODES

Ordovician plate tectonic reconstruction

Chapter

Full-text available

Mar 1991

1991.06

Des granophyres du Cambrien terminal dans le Mont Pourri (Vanoise, zone briançonnaise): première datation U-Pb sur zircon d'un socle des zones internes des Alpes françaises.

Article

Full-text available

Jan 1991

High-Pressure Metamorphism of Phengite Gneisses in the Lower Austro-Alpine Nappe Unit, Eastern Alps: Mineral Equilibria, P–T Parameters, and Age

Article

Full-text available

Nov 1998

Mineral assemblages and the composition of minerals were studied in ortho- and paragneisses of the Lower Austro-Alpine unit (Wechsel and Grobgneis complexes) and the overlying Permian-Triassic metasandstone in the Eastern Alps. The mineral assemblages of these rocks and the compositions of minerals coexisting in them (muscovite-phengite, chlorite, garnet, biotite, tourmaline, albite, and potassium feldspar) are similar and point to metamorphic conditions of the garnet subfacies of the greenschist facies with the Grt + Chl + Phn + Qtz critical assemblage, T = 470-500 degrees C (Grt-Chl and Grt-Bt thermometers), P similar to 10 kbar (Phn-Bt-Kfs-Qtz barometer). The fact that the zoning of the garnet and tourmaline is always prograde and the rocks bear no higher temperature minerals points to the prograde character of metamorphism. This is at variance with preexisting concepts of the retrograde character of metamorphism in the Wechsel and Grobgneis complexes and the occurrence of an older stage of amphibolite metamorphism in them. The U-Pb zircon age of the orthogneisses (metagranites) from the Wechsel Complex, which are metamorphosed to the same grade as the host rocks, indicates that the magmatic crystallization (protolith) age of the parent granite is approximately 603 Ma (Cadomian cycle), and the age of metamorphism under garnet subfacies conditions is similar to 109 Ma (Early Alpine cycle). This explains the similar metamorphic parameters and mineral equilibria in rocks of the Wechsel and Grobgneis complexes and those of the Permian-Triassic cover. Given the general prograde character of the Early Alpine metamorphism, the temperature of the possible pre-alpine (603-109 Ma) metamorphic events in the Wechsel and Grobgneis complexes could not be higher than that of the garnet subfacies.

The Paleozoic metamorphic evolution of the Alpine External Massifs

Article

Full-text available

Jan 1999

The pre-Mesozoic metamorphic pattern of the External Massifs, composed of subunits of different metamorphic histories, resulted from the telescoping of Variscan, Ordovician and older metamorphic and structural textures and formations. During an early period, the future External Massifs were part of a peri-Gondwanian microplate evolving as an active margin. Precambrian to lower Palaeozoic igneous and sedimentary protoliths were reworked during an Ordovician subduction cycle (eclogites, granulites) preceding Ordovician anatexis and intrusion of Ordovician granitoids. Little is known about the time period when the microcontinent containing the future External Massifs followed a migration path leading to collision with Laurussia. Corresponding rock-series have not been identified. This might be because they have been eroded or transformed by migmatisation or because they remain hidden in the monocyclic areas. Besides the transformations which originated during the Ordovician subduction cycle, strong metamorphic transformations resulted from Variscan collision when many areas underwent amphibolite facies transformations and migmatisation. The different subunits composing the External Massifs and their corresponding P-T evolution are the expression of different levels in a nappe pile, which may have formed before Visean erosion and cooling. The presence of durbachitic magmatic rocks may be the expression of a large scale Early Variscan upwelling line which formed after Variscan lithospheric subduction. Late Variscan wrench fault tectonics and crustal thinning accompanied by high thermal gradients triggered several pulses of granite intrusions.

Geochemistry of the metabasites in the Habach formation (Salzburg, Hohe Tauern, Austria). A preliminary report.

Article

Jan 1985

The Habach formation is part of the Palaeozoic basement of the Penninic zone of the Eastern Alps, exposed in the Tauern window. Together with metasediments of partly continental-nearshore origin it consists mainly of metamorphic/magmatic (ophiolitic?) rocks such as serpentinites with rodingites, metagabbros, metabasalts, meta-andesites and metarhyolites. Field and major-element geochemical evidence suggest the presence of two groups of metabasites: Group I are metabasites which are, in places, connected with ultrabasic and gabbroic rocks. They show an iron-enrichment trend in the AFM triangle. Group II metabasites occur spatially with andesites and rhyolites. They follow a calc-alkaline trend. In trace-element geochemistry, group I shows some affinities to island arc, ocean floor or within-plate basalts, with varying TiO2 up to 2.6% and high Zr/Y ratio as well as high Ti/Cr at high Ni. Group II shows more pronounced island-arc characteristics (e.g. low TiO2). Rock/MORB patterns for the two groups allow further subdivision. Group I contains MORB-like as well as island-arc basalts, but with a varying, and sometimes significant, within-plate component. Group II basalts can be interpreted, in a similar way, as island-arc basalts with a certain within-plate component. A back-arc basin, capable of generating a large variety of magmas and probably situated close to an early Palaeozoic continent, is the proposed geological model. (Authors' abstract)-A.W.H.

Die habachformation der typlokalitat zwischen ausserem habachtal und untersulzbachtal (Pinzgau/Salzburg)

Article

Jan 1983

Hans Steyrer

Explanatory note to the international stratigraphic chart

Article

Jan 2000

J. Remane

Notice explicative, carte géol

Article

Kinematics of the Alpine-West Carpathian orogen and palaeogeographic implications

Article

Jan 2001

We present the Euler rotations of the plates involved in the Alpine-West Carpathian orogen. The rotations are defined to a large extent by the magnetic anomalies of the Atlantic Ocean. A few extra rotations occurred during two collisions and a Mid-Cretaceous event. At variance with earlier reconstructions, we additionally control the rotations by the orientation of palaeomagnetic declinations. The plate rotations are integrated into a model illustrated by palaeogeographical maps. Special features of the model are: (1) subdivision of the northern margin of Adria into the two plates, Pelso and Austroalpine-West Carpathia, on the basis of palaeomagnetic data; (2) Eohellenic obduction of Meliata units onto the eastern margins of Pelso and Austroalpine-West Carpathia from the Tethys side; (3) first (Eoalpine) collision of the marginal plates of Adria with Tisza far off the West European plate margin; (4) a 80-90 degrees rotation of Austroalpine-West Carpathia during the Eoalpine collision; (5) subdivision of the: Neoalpine collision into a Palaeogene stage of predominantly strong SE-NW shortening and a Neogene stage of predominantly lateral extrusion westward and eastward. In principle. the maps show quantitative ocean spreading, subduction, and plate rotations. However, possible modifications of the model discussed in this paper limit the quantitative evaluation.

Late Cambrian Mt Pourri granophyres, first dating by U-Pb on zircon of a basement in the internal French Alps (Penninic Alps, Brianconnaise Zone, Vanoise

Article

Jan 1991

The dating of zircons from a granophyric pluton intrusive in the monocyclic pre-Permian series of the Vanoise has given a Cambrian upper intercept age of 507±9 Ma. Petrological data and zircon morphology preclude any heritage. Alpine metamorphic imprints induced an important lead loss in zircon, giving rise to a lower intercept at 49±12 Ma. Lack of evidence for any Hercynian events throws doubts on an omnipresent amphibolite facies metamorphism in the pre-Namurian rocks of the Alpine Inner zones. The Cambrian age measured here allows some correlations with the basement of the Alpine Outer zone. There is an abridged English version. -English summary

Lithostratigraphy and geochemical composition of the Mt. Pourri volcanic basement, Middle Penninic W-Alpine zone, France

Article

Jan 1993

The Mt. Pourri (or Northern Vanoise) massif belongs to the Briancon zone, an internal and metamorphic part of the Alpine belt. The pre-Permian, kilometer-thick sequence is composed of bimodal metavolcanites overlain by carbonaceous black schists containing mafic sills. The abundance of quartz in the felsic rocks points to some degree of alteration especially in the uppermost bimodal layers. The REE-profiles are flat, and the chemical compositions indicate an extensional tectonic setting. In the black schists a felsic-sodic, volcanic-derived component prevails. Towards the top of the bimodal sequence a subvolcanic porphyroblastic granophyre body, dated by the U-Pb method on zircon as Late Cambrian, allows to propose ages for the whole series; Cambrian (bimodal volcanism), Ordovician-Silurian (-? Dinantian) (black schist deposition) and Ordovician to Devonian (-? Dinantian) (sill intrusion) -from Authors

Age constraints on the Cadomian evolution of the Tepl?? Barrandian unit (Bohemian Massif) through electron microprobe dating of metamorphic monazite

Article

Jan 1999

Late Proterozoic and Early Paleozoic Tectonothermal Evolution of the Eastern Alps

Chapter

Jan 1991

Franz Neubauer

The nature and age of the Alpine basement has been a controversial topic of the Alpine geology (e. g. von Raumer 1988). The fossil record begins in the Late Ordovician (for a review, see Schönlaub 1979) except for scarce sporomorphs and acritarchs in metamorphic areas (Giorgi et al. 1979; Reitz and Höll 1988; Sassi et al. 1984) which are not related to continuous Late Ordovician to Carboniferous sections. These data suggest the existence of a distinct late Proterozoic to Early Ordovician sedimentary cycle separated from the later one. Geochronological data from crystalline complexes structurally removed from low-grade sediments favour the presence of a basement metamorphosed and cooled during Early Paleozoic times (for a recent review, see Ebner et al. 1987; Sassi et al. 1987). The relationship between weakly metamorphosed fossiliferous Late Ordovician to Carboniferous strata and crystalline complexes is reviewed in this chapter.

Pre-Alpine evolution in the Southern Carpathians and adjacent areas

Article

Jan 1993

H.G. Krautner

Different associations of pre-Alpine metamorphic rocks were conserved in the main Alpine tectonic units of the Southern Carpathians: Supragetic, Getic, Danubian. Prior to the Alpine cycle they were joined by Variscan napping and by pre-Variscan tectonic transport on the deep-seated ductile shear zone. Thus, the Alpine units include fragments of the Variscan continental crust with different geological evolution in the Paleozoic and in the pre-Cambrian. -Author

Evolution of the Penninic Basement of the Eastern Alps

Chapter

Jan 1993

Penninic basement is exposed in the Venediger nappe system of the Tauern window. Three lithostratigraphic units are distinguished: (1) the ophiolitic Stubach group which consists of splinters derived from back-arc oceanic crust, (2) the Habach-Storz group which is dominated by volcanic protoliths and represents remnants of an island arc probably formed on top of the back-arc oceanic crust, and (3) the Zentralgneis group which is composed of large volumes of Variscan granitoids. The island arc experienced maturation during its evolution in the Late Proterozoic and Early Palaeozoic. Carboniferous high-grade metamorphism and granitoid formation reflect a collisional event and collision- and subduction-related magma generation. S-type, originally cordieritebearing, high-K granitoids, I-type high-K granitoids, and I-type medium-K granitoids form a sequence of decreasing age. Permian magmatism with a tendency to the A-type indicates an intraplate setting and signalizes the end of the Variscan orogenic cycle. The evolution of the basement in the Tauern window shows the progressive buildup of continental crust by long-lived subduction activity, starting in an intra-oceanic environment. The overall picture is reminiscent of granite-greenstone belts.

The Pre-Alpine Evolution of the Continental Crust of the Central Alps — An Overview

Chapter

Jan 1993

D. Gebauer

As for the European Variscides, the continental crust of the Central Alps is part of Gondwana. Geochronologically, this is manifested by a characteristic sequence of geological events presently found in the Brasilian shield or in Africa. However, in contrast to the latter shield areas, the Central Alpine and Variscan crusts consist, in their present erosion level, almost exclusively of recycled Gondwana crust, being geochronologically distinct from continental crust of the other supercontinent, Laurasia. Major Precambrian crust-forming events, as detected by ion-probe dating of detrital zircons from a paragneiss of the Gotthard Massif and a recent river sand from the Po delta, date back to 3.43 Ga and are concentrated around 2.6, 2.1, 1.0 and 0.65 Ga. Precambrian igneous rocks are, as notorious for the European Variscides, very rare in the Central Alps and geochronologically difficult to date. Often they are mafic rocks extracted from a suboceanic mantle, as for example 870-Ma-old gabbros of the Gotthard Massif, metamorphosed to eclogites in the Ordovician (468 Ma). Similar rocks are known from the Berisal complex (Simplon area), the Siviez-Mischabel unit (Valais) and from the southern part of the Penninic nappes. However, their ‘ages’ of ca. 1 Ga still need to be substantiated by further geochronological work, which is also the case for intermediate and felsic orthogneisses of the Upper Austro-Alpine Silvretta nappe.

U-Pb single zircon study of gabbroic and granitic rocks of Val Barlas-ch (Silvretta nappe, Switzerland)

Article

Jan 1997

U. Poller

In Val Barlas-ch, one of the Engadine valleys in the area of the Austroalpine Silvretta nappe, 14 gabbroic samples were investigated by geochemical and geochronological methods. The gabbroic rocks can be divided into fine grained metagabbros, blue quartz bearing "metagabbros" and xenolithic "metagabbros". The country rock of the xenoliths is the Mönchalpgneiss, a former S-type granitoid. The blue quartz bearing "metagabbros" are inferred to be the result of assimilation between a gabbroic intrusion and the Mönchalpgneiss. U-Pb single zircon analyses yielded crystallisation ages around 470 Ma for the fine grained metagabbros and around 528 Ma for the Mönchalpgneiss. The blue quartz bearing "metagabbros" show different zircon types and both ages. Thus the co-existence of a gabbroic and a granitic magma in the late Cambrian is inferred.

The Austro-Alpine Metamorphic Basement East of the Tauern Window

Chapter

Jan 1993

The Austro-Alpine metamorphic basement east of the Tauern window contains various tectono-stratigraphic units which are highly diverse with respect to protolith and metamorphic ages and also geodynamic environment of formation. Early Precambrian elements are represented in certain units, by detrital minerals or possible magmatic rocks. The continuous history started with Late Proterozoic to Cambrian island arc and ophiolite sequences, which were accreted during Late Cambrian and Ordovician tectono-thermal events. These are overlain by fossiliferous Silurian-Devonian shelf sequences. The shelf sequence is contrasted by the Silurian to Devonian active continental margin with partly S-type granite magmatism. Final collision of all units occurred during the Early Carboniferous, involving deep-crustal thrusting, metamorphism, collisional-type magmatism, and subsequent uplift. Sedimentary overstep sequences were deposited at different times from the Early Carboniferous to the Permian, and indicate the progradation of the deformation front within the internal Variscan belt.

Evidence for Lower Paleozoic magmatism in the Eastern Southalpine basement: Zircon geochronology from Comelico porphyroids

Article

Jan 2001

Multigrain conventional U/Pb and single grain 207Pb*/206Pb* evaporation data on zircons are presented for two samples of acidic metavolcanic rocks from the Eastern Southalpine basement (Comelico, North-Eastern Italy). Three zircon populations have been distinguished in each sample, reflecting different contributions in the metavolcanics. Clear, colourless, elongated crystals are thought to be single stage magmatic products, whilst zircons belonging to other populations contain inherited cores mantled by magmatic overgrowths. Elongated crystals yielded concordant U/Pb ages (479 ± 8 and 485 ± 8 Ma), whereas other zircon populations were discordant; the inherited components have poorly constrained Archean apparent ages. Evaporation measurements performed on a core-bearing crystal yielded ages ranging from 646 to 715 Ma, which are interpreted as discordant ages of the core; Th/U zoning also points to a magmatic signature of the inherited cores. The conventional U/Pb data represent the first radiometric age determinations of the pre-Variscan acidic volcanism in the Southalpine domain, and the concordant ages constrain the acidic volcanic activity in the Eastern Southalpine basement within the Arenig. The new isotopic ages are consistent with the biostratigraphy and lithostratigraphy of a nearby basement outcrop (Agordo), which has been correlated to Comelico. Moreover, it is also possible to correlate the Southalpine Ordovician volcanism with a volcanic event in the Austroalpine domain (Eisenerz), for which a comparable age has been inferred by means of biostratigraphy.

Pre-Variscan volcanic activity in the Eastern Alps: The Southalpine porphyroids

Article

Jan 1998

Sandro Meli

Acidic metavolcanics ('porphyroids') are widespread in the eastern Southalpine basement, occurring as thick levels interlayered with Paleozoic phyllites; they often preserve remnants of the original magmatic features not completely annealed by the Variscan metamorphism. More than 200 rock samples coming from six different areas were investigated by XRF and ICP-MS techniques, to detect chemical parameters insensitive to the late- to post-magmatic element mobilization. All the porphyroids are silica-rich and have a peraluminous character. Alkalies and, to a lesser extent, alkali-earth elements, Pb, Zn and Cu, were found to be affected by mobilization, making their use as geochemical tracers somewhat difficult. The major element composition, together with the low contents of Zr, Nb, Hf, Ta, Ni, Co, Cr, V, the negative correlations of Nb, Ta, Zr, Hf vs SiO2, and the high Ba concentrations, suggest a crustal origin for the volcanic protoliths of the porphyroids. The REE patterns are consistent with this interpretation, suggesting that melts have formed by vapour-absent reactions involving metapelites, leaving a granulite-like assemblage in the restite. Some major element trends indicate that the separation between magma and residuum was not always complete. The tectonic discriminant diagrams for acidic rocks do not give straightforward indications, even if a late-to post-orogenic scenario seems most likely, taking into account also the occurrence of cogenetic granitoids in the Austroalpine domain.

Metamorphosed Precambrian mafic rocks from the South Carpathians: Island arc remnants? A geochemical characterization of amphibolites from the Fǎgǎras Mountains, Romania

Article

Jan 1997

This work describes general geochemical features of the Precambrian mafic rocks, mainly amphibolites which occur extensively in two metamorphic formations of the Cumpǎna Group, an important tectonic block incorporated in the Carpathian Belt. Direct and inverse approaches relate the behavior of major and 29 minor, incompatible and compatible elements with the geological environment. The statistical regression of the major element concentrations confirmed the two models according to which most of the amphibolites have originated from basaltic magmas, but at the same time a part of them were derived from mechanical mixtures of a similar igneous component and crustal sediments.The compositions of the possible parental liquids of the least fractionated sample, corrected for olivine crystallization, were in equilibrium with mantle between 15 and 22kb. The REE modeling requires around 5% partial melting of a depleted mantle, initiated in the garnet stability field, possible to exist in hydrous conditions. Furthermore, 20-90% fractional crystallization of a clinopyroxene rich solid and its partial remelting can determine the observed REE abundances and chondrite normalized patterns. The HFSE elemental ratios are characteristic of tholeiitic basalts. On the average, the amphibolites are depleted in Nb and Zr, which is a geochemical feature of continental or island arc tectonic settings. The distribution of transition metal abundances is consistent with the assumption that some parts of the stratigraphic sequence are potential hosts for terrigenous mixing processes. The strato-volcanic structure identified in the lithostratigraphic Group of Cumpǎna can be related with the presence of an incipient island arc.

Central-Western Europe: Major Stages of Development During Precambrian and Paleozoic Times

Chapter

Jan 1991

Christian Pin

The pre-Mesozoic basement of central-western (CW) Europe is exposed in several scattered massifs (Fig. 1). This is because of covering by post-hercynian sedimentary basins, superimposition of the Alpine fold belt, and disruption by the opening of the Bay of Biscay and the Mediterranean system.

The M??nchalpgneiss - Geochemical characteristics and Sm-Nd data of a polymetamorphic S-type granitoid (Silvretta nappe/Switzerland)

Article

Mar 1997
EUR J MINERAL

This paper presents trace element and Sm-Nd isotope data on the Mönchalpgneiss in order to compare the geochemistry of the two polymetamorphic igneous suites that comprise over 30% of the Austro-alpine Silvretta nappe. The first are the so-called "Younger Orthogneisses" of the "Flüelagranitic Association" and the second are the "Older Orthogneisses" including the Mönchalpgneiss which are associated with metagabbros, metadiorites, metatonalites and metagranitoids. U-Pb zircon results from the Mönchalpgneiss are indicative of anatectic processes in late Cambrian to Ordovician times. A volcanic-arc (VA) tectonic environment during intrusion explains the direct association of gabbroic and metagranitoid rocks in the Engadine area. This model is in line with the distribution of major, trace and rare earth elements in these anatectic rocks. However, the significance of the geochemical results remains ambiguous, since the average continental crust and paragneisses of the Silvretta also show VA-type signatures in the respective diagrams. Nd model ages on four Mönchalpgneiss whole-rock samples from the type locality are closely grouped around 1.70 Ga, which is a commonly obtained value for European continental crust. This age is interpreted to be the result of a homogeneous mixture of different crustal components.

K-Ar and U-Pb dating of the metamorphic formations and the associated igneous bodies of the Central South Carpathians

Article

Jan 1983

Variscan events in the basement of the Danubian nappes (South Carpathians)

Article

Jan 1994

The Alpine Basement — Linkage Between Variscides and East-Mediterranean Mountain Belts

Chapter

Jan 1993

The basement of eastern Mediterranean Alpine mountain belts and the extra-Alpine Variscides forms a collage of various tectonostratigraphic units which have been accreted and consolidated during the Variscan orogenic cycle. In consequence, most basement units of the entire Alpine-Mediterranean mountain belts, part of the southern, south-directed segment of the central to west European Variscan collisional belt, have an extension in extra-Alpine Variscides. The evolution of this segment of Variscides reflects processes of an active continental margin since late Precambrian time with both subduction and formation of back-arc basins, and accretion of suspected terranes along the northern Gondwanian margin. Final transpressional collision between crustal pieces of distinct Early Palaeozoic evolution occurred during Early to Late Carboniferous and is followed by molasse-like red bed sedimentation. Subsequent transgression of the Tethyan Sea along the southern margin of Variscides in Late Carboniferous to Permian was associated with dextral transtensive megashearing between Gondwana and Laurussia.

SHRIMP and IDTIMS U-Pb zircon ages of the pre-Alpine basement in the Internal Western Alps (Savoy and Piemont)

Article

Jan 2000

Conventional and SHRIMP II U-Pb age determinations are reported for orthogneiss zircons from four basement units of the Internal Western Alps, and for detrital zircons from the Belledonne External Crystalline Massif (ECM). The results lead to a reappraisal of the geotectonic evolution of the Penninic basements (Brianconnais and Piemont) and their pre-Alpine origin. Except for the emplacement of the Cogne granodiorite (Valle d'Aosta) dated at 357 ± 24 Ma (conventional IDTIMS analyses) and 356 ± 3 Ma (SHRIMP analyses), little evidence has been found for a Variscan imprint. However, results from the Peclet orthogneiss (482 ± 5 Ma - SHRIMP) and Modane metagranite (452 ± 5 Ma - SHRIMP) in the Sapey gneiss unit, and the Ambin metarhyolite (500 ± 8 Ma - SHRIMP) from the Ambin massif, show that a major plutonic and tectonic event occurred at 450-500 Ma. Evidence has also been found for a major plutonic event of Permian age (269 ± 6 Ma SHRIMP age from the Gran Paradiso orthogneiss) which suggests important Paleotethyan activity at least in the Piemont basement. SHRIMP dating of detrital zircons from a metasediment of the Belledonne massif (ECM) and zircon cores and xenocrysts found in most of the analysed magmatic rocks show a large Pan-African age component (590-630 Ma) in both the External and Internal Alps. This suggests that there is little difference in the composition of the basement between (1) the ECM, which show a clear continuity with Variscan Europe, (2) the Penninic basements, which may represent allochthonous Alpine terranes, and (3) the Southern Alpine and Austro-Alpine domains, classically attributed to an "African" indenter. They all belong to Gondwana but differ strongly in their Variscan and Alpine history.

Time constraints on the pre-Variscan magmatic/metamorphic evolution of the Gotthard and Tavetsch units derived from single-zircon U-Pb results

Article

Jan 1994

Polymetamorphic mafic-ultramafic rock associations preserving relic HP-HT mineralogy represent the oldest igneous remnants so far identified in the pre-Variscan Helvetic basement of the Central Swiss Alps. In order to establish time constraints on the origin of these important tracers of early basement evolution, three eclogitic metagabbro samples of island-arc affinity (Gotthard and Tavetsch units) and one basaltic eclogite of MORB affinity (Gotthard unit) have been dated by conventional high-resolution single-zircon U-Pb isotope techniques. -from Authors

Pre-Alpine geochronology of the Central, Western and Southern Alps

Article

Jan 1999

Geochronology plays a crucial role in unravelling the complex and polyphase evolutionary history of the Alpine basement. In this review, mostly recent data will be used to set up an 'orogenic timetable' for the pre-Alpine evolution, starting with Archean information hidden in zircon cores and finishing with widespread metasomatic alterations of Triassic/Liassic age, detected best in the Southalpine domain. The evolution of the Alpine basement confined by these age limits comprises post-Panafrican clastic sedimentation on the Gondwana shelf, the Cambrian - Early Ordovician oceanic period, Devonian mafic and felsic magmatism, orogenic cycles in the Ordovician and Permo-Carboniferous and voluminous magmatism at different moments during this evolution.

The Habach-Formation and the Zentralgneis — A Key in Understanding the Palaeozoic Evolution of the Tauern Window (Eastern Alps)

Chapter

Jan 1993

Volker Hoeck

The pre-Permian Habach formation is a complicated metamorphosed sequence of magmatic and sedimentary rocks within the Tauern window. It can be separated into three subunits: 1. Ophiolites including the Basisamphibolit; 2. An island arc volcanic sequence; 3. The Eiser sequence (Biotitporphyroblastenschiefer). The ophiolites consist of metamorphosed ultramafic and mafic plutonics as well as volcanics. Their chemistry resembles that of basalts from a marginal basin with some MORB characteristics. The island arc sequence consists of basaltic to rhyolitic rocks overlain by sediments. The volcanics display a geochemical pattern consistent with an island arc volcanic series formed on continental crust. The Eiser sequence comprises pelitic and psammitic metasediments interlayered by basic to acidic metavolcanics. The few analyses available indicate a possible oceanic island arc sequence. Age data from all subunits of the Habach formation based on radiometric data and scarce fossil findings range from the Upper Proterozoic to the Carboniferous. The evolution of the Habach formation despite the uncertainty of the age dating fits a model of a long-lasting active continental margin on which different terranes were accreted during the Upper Proterozoic to the Palaeozoic.

Archean and Proterozoic ancestry in late Precambrian to early Paleozoic crustal elements of southern Turkey as revealed by single- zircon dating

Article

Jan 1990
GEOLOGY

Detrital zircon ages and paleontology limit the age of the oldest known metasedimentary rocks in the Menderes-Taurus block of southwestern Turkey to between 657 ± 5 Ma and Middle Cambrian (ca. 533 Ma). A mylonitic granite, also part of the basement, yielded a date of intrusion of 543 ± 7 Ma. The scatter of both detrital and xenocryst zircon ages between 612 ± 6 and 3140 ± 2 Ma virtually precludes northeastern Africa and Arabia as their provenance, but is compatible with a source in the Angara craton of Siberia. These results suggest that the Pan-African evolution in the Middle East may have ended by Angara's collision with Gondwana in the Early Cambrian. -Authors

Jungproterozoische Mikrofossilien aus der Habachformation in den mittlern Hohen Tauem und dem nor-dostbayerischen Grundgebirge

Article

Jan 1988

Zusammenfassung Für Teile der Habachformation in den Hohen Tauern wird erstmals eine biostratigraphische Altersbestimmung vorgelegt. Sie stützt sich auf Mikrofossilvorkommen in Phylliten ("Ha-bachphylliten") des Habachtals und in gebänderten Metasedi-menten (Muskovit-Chlorit-Biotit-Albit-Schiefer und Graphit-Quarzite) aus der Basisschieferfolge am Osthang des Felber-tals westlich vom Brentling. Die Habachphyllite enthalten Acritarchen, die für den Zeit-raum Oberriphäikum bis Untervendium bezeichnend sind. Die Basischieferfolge hat nur Reste von coccoiden Cyanobakte-rien geliefert. Diese erlauben keine genaue s!ratigraphische Einordnung, denn Cyanobakterien dieses Typs sind im ge-samten Porterozoikum weit verbreitet. Ähnliche Spektren wie in den Habachphylliten haben sich in Phylliten aus der Prasinit-Phyllit-Serie am Südrand der Münchberger Gneismasse gefunden, dort mit Acritarchen des unteren Vendiums.

Ordovician Plate Tectonic Reconstructions

Technical Report

Mar 1990

1990.07 Superseded by: Scotese, C.R. and McKerrow, W.S., 1991. Ordovician plate tectonic reconstructions, in Advances in Ordovician Geology, C.R. Barnes & S.H. Williams (editors), Fifth International Symposium on the Ordovician, Geological Survey of Canada Paper 90-9, p.271-282

1.57-Ga Magmatism in the South Carpathians: Implications for the Pre-Alpine Basement and Evolution of the Mantle under the European Continent

Article

Mar 1999

Chemical and isotopic analyses of amphibolites and gneisses from the oldest lithostratigraphic group in the South Carpathians produce new insights regarding the chronology and evolution of the mobile Proterozoic crust in central-eastern Europe. These results date an episode of magmatism related to oceanic crust consumption, reveal a period of continental stabilization, and put constraints on the underlying mantle composition. Amphibolites from the Cumpana Group have their origin in basalts, chemically similar to island arc tholeiites. A whole-rock isochron age of 1.57 ± 0.09 Ga records the oldest magmatic event found in the Carpathians. It corresponds to the development of a primitive island arc and reflects the most recent isotopic equilibrium, achieved during magmatic crystallization and solidification in pre-Grenvillian time. The depleted source, implied by an initial value of ε(Nd) = +6.4 at 1.57 Ga, is comparable to that of the 0.8 Ga Dragsan metatuffs, located approximately 100 km to the southwest of the Cumpana Group. It is assumed that a Dalslandian event could have isolated these structures in the Precambrian. A period of almost 800 m.yr. accounts for the homogeneity of a dynamic and depleted mantle, which was probably enriched around 800 Ma, precluding a stable pre-Variscan central-eastern European continent. The Sm-Nd mineral isochron ages, between 323 and 358 Ma, show Variscan recrystallization ages of the metatholeiites from the Cumpana Group. Their present whole-rock 87Sr/86Sr values vary widely between 0.7039 and 0.7079 without any isochron trend, suggesting Rb mobilization. The Rb-Sr mineral isochrons show partial isotopic equilibration during younger tectonothermal events, probably reflecting the Alpine orogeny. The K-Ar mineral ages of amphibolites are also Variscan, with some exceptions due to Ar loss caused by early Alpine events. We therefore recommend a reevaluation of the Precambrian cores from the Carpathians on the basis of Nd radiometric methods, which are able to overcome the problems of isotopic partial reequilibration during multiple metamorphisms of the original rocks.

Notice Explicative, Carte géol. France (1/50 000), Feuille Domène (773)

Book

Jan 1998

Evolution of late Neoproterozoic to early Paleozoic tectonic elements in Central and Southeast European Alpine mountain belts: Review and synthesis

Abstract

No full-text available

Recommended publications

Synchronous formation of the metamorphic sole and igneous crust of the Semail ophiolite: New constra...

Evidence for ophiolite obduction, terrane accretion and polyorogenic evolution of the north Scandina...

Orogeny can be very short

Some Like It Cold: The “Conundrum of Samail” Revisited