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The Grenvillian and Pan-African orogens: World's largest orogenies through geologic time, and their implications on the origin of superplume
Abstract
The Neoproterozoic Earth was shaped largely by the Grenvillian and Pan-African orogenies. Out of these, the Grenvillian orogeny has long been regarded to be of minor nature in terms of global-scale orogenic episodes, whereas the Pan-African orogeny has been widely recognized in many continental fragments, although not in major parts of Asia. Based on chronological information in zircons from major river mouths across several important terrains of the globe, we show here that the Grenvillian orogeny contributed significantly to the formation of the continental crust. The time period between 0.6 Ga and 0.8 Ga marked the climax at the dawn of the Pan-African orogeny. Continental crust formed in this period is concentrated in the Pan-African orogenic belts widely across the globe. These regions were widespread over the half hemisphere of the globe, and were subsequently reduced in size after they moved to form Laurasia. The normalized frequency distribution of zircon ages from river-mouth sand over the world clearly demonstrates that Neoproterozoic and (0.9–0.6 Ga) and Grenvillian (1.3–1.0 Ga) peaks define the largest population. This means that extensive subduction, and hence active plate tectonics, might have operated through these periods. The zircon study has also brought to light new regions of the Grenvillian orogenic belts, particularly in the continents which are now covered by thick Phanerozoic sedimentary basins. Based on the new locations of Grenvillian orogens identified in this study, and using the distribution patterns as a marker bed, we propose revised paleogeographic configurations of the Rodinia and Gondwana supercontinents.
... The occurrence of these grains in fluvial deposits with palaeo-current flow towards the west and northwest (Eriksson, 1979(Eriksson, , 1981(Eriksson, , 1986 supports the argument for a distinct source terrain in the east. For example, this source could have been the "Eastern Highlands" (Ryan & Whitfield, 1979) and the western Antarctic Haag Nunataks terrain that was likely situated to the southeast of the basin (Jacobs et al., 2008;Jordan et al., 2020;Rino et al., 2008). Finally, the occurrence of rare mafic volcanic lithic fragments in the uppermost Clarens Formation at Talon (Figure 6c) may indicate the incorporation of primary volcanic material, further supporting the idea of an earlier onset of basaltic volcanism in the southern part of the Clarens basin relative to the north (see below and Bordy et al., 2021;Moulin et al., 2017). ...
... (Pan-African) age fraction that can be linked to the Damara and Saldania belts during the formation of Gondwana (Figure 12; Foster et al., 2015;Frimmel et al., 2013;Rino et al., 2008). The Damara Belt consist of basal coarse clastic sedimentary rocks of the Nosib Group, which is overlain by meta-turbidites and other metasedimentary successions of the Swakop Group (Foster et al., 2015) with a zircon age fraction of 600-900 Ma, specifically in the northern part. ...
... A Tonian to Stenian (Grenvillian) age fraction is the second most abundant, and sedimentary source terranes with this age range can be attributed to the genesis of the Namaqua-Natal Mobile Belt (Figure 12; Bial et al., 2015: 1350-1100 and the western Sierras Pampeanas (Rapela et al., 2010: 1330-1030. These metasedimentary sequences are part of the Grenvillian orogen of western Gondwana, with a prominent age peak between 1.0 and 1.2 Ga (Figure 12; Casquet et al., 2006Casquet et al., , 2008Rino et al., 2008;Rapela et al., 2010). ...
The Clarens Formation is a widespread aeolianite deposited over southern
Gondwana and represents the final phase of erg evolution in the main Karoo Basin
during the Early Jurassic. Previous age assessments of the formation hinge on limited
detrital zircon data, supplemented by relative ages from the biostratigraphy
and geochronology of the adjacent Karoo units. This study refines the depositional
history of the Clarens Formation, including its sediment source dynamics as well
as basin-wide
geochronological framework, based on U–Pb dating of detrital zircon
grains, together with petrographic and sedimentological characterization. The
abundant presence of heavy minerals like zircon, tourmaline and rutile suggests
large-scale
detritus recycling, while the uniform sandstone composition on a regional
scale is an indication of sediment homogenisation across the basin. Based
on the prominent detrital zircon age fractions, the sediments are interpreted as
having been reworked from pre-existing
rocks of the Karoo Supergroup (Permian),
the Damara and Saldania Orogenic belts (650–490 Ma), whereas minor sources
can be assigned to the Namaqua-Natal
Mobile Belt (1.35–1.1 Ga) and the western
Sierras Pampeanas (1.30–1.33 Ga). Unstable minerals (hornblende, garnet, titanite,
feldspar) provide evidence for a nearby granitic source east and southeast of the
basin, related to likely Grenvillian rocks (1.0–1.3 Ga). An Early Jurassic zircon age
fraction is linked to volcanic activity in the Chon Aike Magmatic Province that, at
the time, was situated south and southwest of the study area. Maximum depositional
ages derived from these detrital zircon dates suggest that the sedimentation
of the Clarens Formation spanned an interval of ~10 Ma during the Pliensbachian
and early Toarcian. More specifically, the lower part of the formation is of early
Pliensbachian age or younger (~191–192), while the upper part is of early Toarcian
age or younger (~181–183 Ma). These age patterns are particularly prominent in the
south of the basin that was situated closer to the volcanic source.
... Consequently, whereas some paleomagnetic reconstructions of the past two decades are supportive of the supercontinent (e.g., Dalziel, 1997Dalziel, , 2013Meert and Lieberman, 2004;Scotese, 2017) (Figs. 2a, c, f), others are equivocal (e.g., Cordani et al., 2003;Rino et al., 2008;Robert et al., 2018) (Figs. 2b, d), and yet others refute its existence (e.g., Li et al., 2008;Merdith et al., 2017Merdith et al., , 2021Zhao et al., 2018;Wen et al., 2020;Robert et al., 2020Robert et al., , 2021Evans, 2021) (Figs. ...
... The timing of the collisional orogenesis of assembly spans the broad interval ca. 700-500 Ma, with peaks at ca. 650-600 Ma and 570-530 Ma, based on the ages of associated magmatism and metamorphism (e.g., Meert, 2003;Kröner and Stern, 2004;Oriolo et al., 2017;Schmitt et al., 2018), and inferred from the age spectra of detrital zircon and monazite in modern river systems (e.g., Rino et al., 2008;Itano et al., 2016). ...
... 580 Ma (Meert and Lieberman, 2004), (d) ca. 540 Ma (Rino et al., 2008), (e) ca. 600 Ma ), (f) ca. ...
Following a decade during which its presence was widely accepted, the existence of the putative Ediacaran supercontinent Pannotia has come into question since the turn of the millenium, largely due to the geochro-nology of Ediacaran-Cambrian orogens, which suggests that the supposed landmass had begun to break up well before it was fully assembled. Paleomagnetic data from this time interval have been used to both support and refute the existence of Pannotia, but are notoriously equivocal. Proxy signals for Ediacaran-Cambrian super-continent assembly and breakup, although collectively compelling, can be individually challenged, and efforts to detect the mantle legacy expected of supercontinent amalgamation, while promising, are inconclusive. Yet the existence of Pannotia is central to the nature, duration and evolution of the supercontinent cycle, and dictates the cycle's geodynamic pathway from the breakup of Rodinia to the assembly of Pangea. Hence, the question of Pannotia's existence, like that of Hamlet, is one of fundamental importance and demands far more attention than it has hitherto received.
... The Neoproterozoic Pan-African orogeny (Fig. 1a) is the most extensive orogenic system preserved on the Earth and triggered the major continental crust formation during the Neoproterozoic era (Grantham et al., 2003;Rino et al., 2008). The Pan-African orogens formed during the continental amalgamation of the Pannotia/Greater Gondwana supercontinents (Rino et al., 2008;Torsvik & Cocks, 2013;Nance & Murphy, 2019). ...
... The Neoproterozoic Pan-African orogeny (Fig. 1a) is the most extensive orogenic system preserved on the Earth and triggered the major continental crust formation during the Neoproterozoic era (Grantham et al., 2003;Rino et al., 2008). The Pan-African orogens formed during the continental amalgamation of the Pannotia/Greater Gondwana supercontinents (Rino et al., 2008;Torsvik & Cocks, 2013;Nance & Murphy, 2019). Pan-African orogens are hot: typically characterized by voluminous orthogneiss, migmatite, and granite with some granulites and minor eclogites. ...
... The EAO has a sequence of rocks with an age span of 950-450 Ma (Kröner, 1984). The oldest Pan-African continental collision has been tracked to ∼800 Ma, but its major accretionary/collisional cycle is dated as 650-500 Ma (Kröner et al., 1990;da Silva et al., 2005;Rino et al., 2008). ...
In collision-type orogens, where high-pressure and ultrahigh-pressure (HP–UHP) metamorphism usually occurs, deeply subducted continental slabs with eclogitized mafic rocks often undergo recrystallization/overprinting with various geothermal gradients after the peak conditions at lower-to-middle-crustal levels. During the crustal stabilization, the transition from eclogite- to granulite-facies is common. We conducted metamorphic petrology and zircon geochronology on (1) bimineralic and (2) partially granulitized eclogites from the Neoproterozoic Ufipa Terrane (Southwestern Tanzania). Microtextural relationships and mineral chemistry define three metamorphic stages: eclogite metamorphism (M1), HP granulite-facies overprinting (M2), and amphibolite-facies retrogression (M3).
The bimineralic eclogite has a basaltic composition and lacks M2 minerals. In contrast, the kyanite eclogite is characterized by a gabbro-dioritic whole-rock composition and contains inherited magmatic zircon. Although the matrix is highly granulitized, garnet and kyanite contain eclogite-facies mineral inclusions. Phase equilibria modeling revealed P–T conditions of ~2.1–2.6 GPa and ~650–860°C for the M1 stage, and ~1.4–1.6 GPa and ~750–940°C for the M2 stage. Zircon with eclogite-facies mineral inclusions from the bimineralic eclogite lack Eu anomaly in the REE patterns and yielded the M1 eclogite metamorphic age of 588 ± 3 Ma. Zircon overgrowths surrounding the inherited Paleoproterozoic magmatic cores in kyanite eclogite yielded 562 ± 3 Ma. A weak negative Eu anomaly in the REE patterns and the absence of eclogitic mineral inclusions suggest the zircon growths at the M2 HP granulite-facies metamorphic stage. These new data indicate an eclogite- to granulite-facies transition time of 26 ± 4 million years (Myr), suggesting a rate of HP rock exhumation toward a lower crustal level of ~0.7–1.5 mm/yr. Furthermore, the density evolution model indicates that buoyant host orthogneiss with low-density gabbro-dioritic eclogite, plays an important role in carrying high-density basaltic eclogite. Our 2D thermomechanical modeling also suggests that a slab break-off with a lower angle subduction of <~20° triggers the exhumation of the HP slab sliver with ~20–30 Myr eclogite-to-granulite transition time of large HP–UHP terranes in major collision zones.
... The Río Paraná extends for nearly 5000 km and has a drainage basin of 2.5*10 5 km 2 that includes both southern Brazil and the Eastern Cordillera of the Central Andes. Bedrock in the basin is highly variable but basement rocks consist primarily of Pan-African age units (Rino et al., 2008). Modern river sediments reflect this with dominant detrital zircon populations of Pan-African age ( Fig. 3; Rino et al., 2008). ...
... Bedrock in the basin is highly variable but basement rocks consist primarily of Pan-African age units (Rino et al., 2008). Modern river sediments reflect this with dominant detrital zircon populations of Pan-African age ( Fig. 3; Rino et al., 2008). Although the data are associated with a relatively small n (25), roughly 75% of detrital zircons in the Río Paraná have ages between 500 and 700 Ma. ...
The Pampas of Argentina contain a broad distribution of Pleistocene to Holocene loessic sediments and eolian dune deposits. Models describing the sediment provenance of this eolian system have, at times, conflicted. We address the provenance of these deposits through U-Pb detrital-zircon geochronology. Our results indicate broad similarity in age distributions between samples, with a dominant Permian-Triassic mode, and widespread but lesser Cenozoic, Devonian-Mississippian, Ediacaran-Cambrian, and Mesoproterozoic modes. These data are inconsistent with a large contribution of detritus from Patagonia as previously suggested. These data are consistent with very limited contribution of first cycle volcanogenic zircon to the Pampean eolian system, but abundances of older Neogene zircon indicate proto-sources in the Andes. The ríos Desaguadero, Colorado, and Negro contain populations that were likely within the dust production pathways of most of the loess, paleosol, and eolian dune deposits, but the derivation of the zircon ages in these sediments cannot be explained solely by these river systems. One statistical outlier, a loess sample from the Atlantic coast of the Pampa region, indicates quantitative similarity to the age spectra from the ríos Colorado and Negro, consistent with derivation from these subparallel rivers systems during subaerial exposure of the continental shelf under high global ice-volume. Another statistical outlier, a paleosol sample from the Río Paraná delta region, has zircon ages more closely associated with sediments in the Paraná region than in rivers south of the Pampa region. Collectively, these data point to the complexity of the Pampean eolian system and substantial spatial-temporal variation in this Pleistocene−Holocene eolian system.
... The Río Paraná extends for nearly 5000 km and has a drainage basin of 2.5*10 5 km 2 that includes both southern Brazil and the Eastern Cordillera of the Central Andes. Bedrock in the basin is highly variable but basement rocks consist primarily of Pan-African age units (Rino et al., 2008). Modern river sediments reflect this with dominant detrital zircon populations of Pan-African age ( Fig. 3; Rino et al., 2008). ...
... Bedrock in the basin is highly variable but basement rocks consist primarily of Pan-African age units (Rino et al., 2008). Modern river sediments reflect this with dominant detrital zircon populations of Pan-African age ( Fig. 3; Rino et al., 2008). Although the data are associated with a relatively small n (25), roughly 75% of detrital zircons in the Río Paraná have ages between 500 and 700 Ma. ...
... The western Gondwanan margin of present-day Argentina consists of an assemblage of accreted terranes (Pampia, Cuyania, and Chilenia), igneous intrusions, and subsequent metamorphosed units (Ramos, 1988;Pankhurst et al., 1998;Ramos et al., 1998Ramos et al., , 2015Rapela et al., 1998Rapela et al., , 2007Rapalini, 2005;Dahlquist et al., 2010). The Pampia terrane, also known as the Sierras Pampeanas, accreted to the Gondwanan margin during the Neoproterozoic to Cambrian (Rapela et al., , 2007Rino et al., 2008;Ramos et al., 2015). The Sierras Pampeanas are subdivided into two regions: (1) Eastern Sierras Pampeanas, (2) Western Sierras Pampeanas (see discussion below). ...
The Late Paleozoic Ice Age (LPIA) was a principal control of sedimentation across Gondwana from the late Devonian through early Permian. We assess the hypothesis that glacial to interglacial transitions in western Argentina were the primary control influencing sediment routing patterns among the various Carboniferous-Permian basins in western Argentina. The Carboniferous Ansilta Formation consists of glaciomarine, nearshore, and fluvial systems deposited during the LPIA along the eastern margin of the Calingasta-Uspallata Basin in Argentina. The lower, glacially influenced succession of the Ansilta Formation records at least five glacial advances; the upper succession of consists of progradational shallow marine, deltaic, and fluvial strata. We combine 1225 new U–Pb zircon ages from six samples of the Carboniferous Ansilta Formation in the Calingasta-Uspallata Basin with 5864 U–Pb ages from 147 published samples in the detritalPy-mix forward mixture model to characterize provenance shifts. For the glacially influenced lower Ansilta Formation, sediment was derived locally from the Protoprecordillera, which was a prominent highland with alpine glaciers flowing west and east into the Calingasta-
Uspallata and Paganzo basins, respectively. Thus, there was little or no connection between these two basins during Serpukhovian-Bashkirian glaciation. The fluvial/deltaic upper Ansilta had distal sediment sources in the Sierras Pampeanas. Furthermore, our results support the collapse of the Protoprecordillera topographic
barrier, enabling drainage patterns connecting the Paganzo and Calingasta Uspallata basins by late Pennsylvanian-early Permian time.
... These orogenic systems are usually grouped into the Brasiliano/Pan-African Tectonic Cycle (e.g. Brito Neves et al. 1999;Rino et al. 2008) and are mostly located in South America, Africa and southern India (e.g. Schmitt et al. 2018). ...
... By contrast, using the relative age of oceanic crust, Murphy and Nance (2003) identified Gondwana (or Pannotia) to have formed by extroversion from Rodinia, that is, by preferential subduction of the Mirovoi Ocean exterior to Rodinia, with Pangaea forming by introversion, that is, by subduction of the oceans (Iapetus, Rheic) that formed due to the breakup of Pannotia. The ambiguity in the definition of interior and exterior oceans has led to Columbia, Rodinia and Gondwana being described as forming by extroversion and introversion by different workers (Hoffman 1991;Murphy and Nance 2003;Rogers and Santosh 2003;Rino et al. 2008;Oriolo et al. 2017;Li et al. 2019Li et al. , 2023. ...
Supercontinent amalgamation is described by the end-member kinematic processes of introversion - closure of interior oceans; extroversion - closure of exterior oceans; or orthoversion - amalgamation 90° from the centroid of the previous supercontinent. However, supercontinent formations are often ascribed to contradictory mechanisms; for example, Pangea has been argued to have formed by introversion from Pannotia/Gondwana, and extroversion from Rodinia. Conflicting interpretations arise partly from attempting to define oceans as interior or exterior based on paleogeography, or the age of the oceanic lithosphere relative to the time of supercontinent breakup. We define interior and exterior oceans relative to the external subduction ring, and associated accretionary orogens that surround amalgamated supercontinents. All oceans within the continental dominated cell and internal to the subduction ring are interior oceans. The exterior ocean is separated from the interior oceans by the subduction ring and bordered by external accretionary orogens. Wilson cycle tectonics dominate the interior continental cell, conversely, subduction of the exterior ocean is doubly vergent and lacks continent-continent collision. For the exterior ocean to close, the subduction ring must collapse upon itself, leading to the collision of external accretionary orogens. Employing this definition, Rodinia formed by extroversion, but all other supercontinents formed by introversion.
... However, there is a debate about whether it came from the northern margin of India or Australia. Since the beginning of this century and Rino et al., 2008). Ind, India; Au, Australia; Ant, Antarctic; Kal, Kalahari; SF, San Francisco; Con, Congo; Lau, Laurentia; Rio, Rio de la Plata; Amz, Amazonia; Ba, Baltica; W.Af, West Africa; Sib, Siberia; ANS, Arabian-Nubian Shield; AFB, Albany-Fraser orogen; EGB, Eastern Ghats orogen; KB-IB, Kibaran and Irumide orogens; G, Greenville orogen. ...
The composition and geological evolution of pre-Cryogenian material in the Tibetan Plateau and its surrounding areas have played an important role in studying the formation and evolution of early supercontinents on Earth. This paper systematically summarizes the characteristics of pre-Cryogenian sedimentation, paleontology, magmatism, and metamorphism in the Tibetan Plateau and its surrounding areas. Based on existing data, the records of pre-Cryogenian sedimentation and paleontology are mainly concentrated in the Meso–Neoproterozoic, with relatively few records from the Paleoproterozoic or earlier. The oldest geological record is the Hadean detrital zircons in the metamorphosed sedimentary rocks of the Himalaya and Qamdo areas (ca. 4.0 Ga). The Tibetan Plateau and surrounding areas preserve records related to the formation and evolution of the Kenor supercraton, and the Columbia, Rodinia, and Gondwana supercontinents. Pre-Cryogenian basements can be divided into three types: Tarim-, Yangtze-, and Lhasa-type. The Tarim-type basement has a paleogeographic affinity with the northern margins of the Australian and Indian continents and lacks detrital zircon age peaks and magmatic-metamorphic records related to the Rodinia assembly (ca. 1.3–0.9 Ga). The Yangtze-type basement records volcanic activity related to global cooling in the latest pre-Cryogenian period and contains Meso–Neoproterozoic stromatolite and micropaleoflora fossils, as well as magmatic-metamorphic records related to Rodinia assembly (ca. 1.1–1.0 Ga). The Lhasa-type basement is characterized by Neoproterozoic rift-related sediment records (ca. 900 Ma) and high-pressure metamorphic events (ca. 650 Ma), with a prominent peak of detrital zircon ages of ca. 1.2–1.1 Ga. It is likely to have a paleogeographic affinity with the African continent.
... The exact cause of initiation of the compressive deformation cannot be inferred with full conBdence either. However, the terminal stage of the Mesoproterozoic coincides well with the Grenvillian amalgamation (Deb 2003;Saha and Chaudhuri 2003) related to the formation of the Rodinia supercontinent (HoAman 1991;Mloores 1991;Torsvik et al. 1996;Dalziel et al. 2000;Meert and Torsvik 2003;Rino et al. 2008). The eAect of this compressive event may have manifested in the deformed Chanda Limestone as the far-Beld eAect of the Grenvillian orogeny, characterised by mapscale folds and mesoscopic compressive structures such as thrusts and folds of varying tightness and attitudes. ...
The Mesoproterozoic Penganga Group of Pranhita–Godavari valley basin in south India comprises a succession that starts with a coarse sandstone–conglomerate unit at the base and is successively followed by sandstone, limestone and shale in the order of younging. The complete succession, without any hiatus, is believed to have accumulated during a transgression caused by the progressive deepening of the basin floor as a result of continuous rifting. However, the finding of some stromatolitic limestone at the top of the sequence contradicts the idea of a continuous deepening of the basin. The present study, on the contrary, proves that a phase of deformation induced regression in parts of the basin interjected the regional transgressive phase. The deformational episode caused an uplift of the basin floor and consequent reversal of the basinal slope towards the southwest, which was syn-kinematic to sedimentation. This deformation event triggered sub-marine erosion of the sediments in and around the zone of deformation, while away from it, there is a record of uninterrupted sedimentation. The stromatolitic limestone, deposited on top of the pre-inversion-eroded sediments, is now considered the youngest formation of the Penganga Group.
... Ga old Eburnean orogeny (Zhao et al., 2002). The Grenville event formed the Rodinia supercontinent in Mesoproterozoic (Rino et al., 2008) that resulted in the recent Kibaran orogeny along the Pharusian and Oubanguides Mobile Belts (Tack et al., 2008). In Central Africa, orogens associated with the Rodinia construction were formed by the convergence of the Congo Craton with the Kalahari, Bangweulu, Tanzania, Uganda, and West-Nilian cratonic blocks. ...
We use seismic surveys (853 stations and 79 seismic profiles) to compile a new continental Moho model of the African continent of which 90% is formed by the Precambrian crust. The result reveals considerable Moho depth variations, with values ranging from 14-20 km for the Afar Triple Junction and Turkana Lake to 46 km beneath the Rif Mountains, parts of the Ethiopian Plateaus, and the Namaqua-Natal Belt. A localized Moho deepening (∼44 km) is found beneath the western and eastern blocks of the Congo Craton, the central part of Victoria Lake, the Rehoboth Province, the eastern part of the Kaapvaal Craton, and the Irumide Belt. A shallow Moho depth is detected beneath wide areas in North, Central, and East Africa, particularly along the North Africa coast (24-30 km), the Mauritanian Belt (26-30 km), the West and Central African Rift System (30-32 km), the Benue Trough (24-28 km), and beneath the Rwenzori Mountains (26-30 km) and the southern part of Somali Plate (22-26 km). At many locations, a Moho relief is characterized by significant changes across different tectonic provinces; from the Afar Triple Junction, Turkana Depression, and the Somali Plate to the Main Ethiopian Rift, between the Rwenzori region, from the Gabon-Cameroon Shield to the Benue Trough, and from the western border of the West African Craton to the Mauritanian Belt. According to our estimates, an average Moho depth beneath the African continent is 36.1 km. Comparison of our result with selected global, continental, and regional Moho models shows large differences that locally even exceed ±15 km.
... (5) Teya granite-gneiss dome. (b) Configuration of the core of Rodinia and foldbelts of Grenville orogeny during its stabilization (blue, modified after Rino et al., 2008. Setting of the Siberian craton is according to (Metelkin et al., 2012). ...
Abstract—The paper provides evidence that collisional magmatism related to the Neoproterozoic (880−860 Ma) orogenic event occurred in the southwest of the Siberian Craton. Newly obtained data are presented on the major-component and trace-element composition, U−Pb (SHRIMP II) zircon age, and Sm−Nd isotope composition for rocks of the Gusyanka granitoid massif in the Yenisei fault zone of the Yenisei Ridge. The concordant U−Pb zircon age of the Gusyanka massif is 871 ± 11 Ma indicates that its rocks were formed in the mid-Early Neoproterozoic, simultaneously with the rocks of the Kalama and Eruda massifs in the Tatarka−Ishimba fault system, during the same stage of the collisional events at approximately 880–860 Ma. The calc-alkaline granites, granodiorites, and leucogranites of the Gusyanka massif are classified, on the basis of their high alumina content and trace element composition, as S-type and were derived from a metapelitic source. Many trace-element parameters of rocks of the Kalama and Eruda massifs correspond to those of low-potassium I-type granites, which were most likely derived from mafic rocks and tonalites. The granitoids of the Gusyanka massif, on the one hand, and the Kalama and Middle Tyrada massifs,
on the other, differ contrastingly in Nd isotope composition. The source of the former was either metapelites of the Tungusik Group or metasedimentary rocks of the Sukhoi Pit Group, with the involvement of juvenile material. The melts of granites of the Kalama and Middle Tyrada massifs might have been derived from a source with the involvement of an older, possibly Paleoproterozoic, crustal material and a juvenile mafic source. Thus, the orogenic events at 880−860 Ma led to the generation of melts at different levels of the Paleo- to Mesoproterozoic crust of the trans-Angara region of the Yenisei Ridge. The geodynamic history of the region is correlated with the synchronous successions and similar style of tectono-thermal events along
the peripheries of the large Precambrian cratons of Laurentia and Baltica, and this is consistent with paleocontinental reconstructions of the close spatiotemporal relations between these cratons, Siberia, and their incorporation into Rodinia.
... Various models that deal with the progressive assembly of Gondwana have been proposed [2][3][4][5][6]22,23 . Recently, coeval Neoproterozoic orogenic activity was identified in the Tarim craton 24 and the Lhasa Terrane hinting at possible links to orogenic events in eastern Gondwana 25 . ...
The serpentine orogenic belts that formed during the Neoproterozoic assembly of Gondwana resulted in geodynamic changes on the planet in advance of the Cambrian radiation. The details of Gondwana assembly associated with the closure of the Mozambique Ocean are enigmatic. We compile published geological and paleomagnetic data to argue that the Tarim block was associated with the Azania and Afif-Abas-Lhasa terranes and they were the locus of long-lived Andean-type subduction during the~900-650 Ma interval. Our model suggests a subduction system reorganization between 750-720 Ma, which resulted in two distinct phases of Mozambique ocean evolution. Between 870-750 Ma, a N-S oriented subduction system marks the locus of ocean crust consumption driven by the extension of the Mozambique Ocean. Beginning~720 Ma, a newly developed~E-W oriented subduction system began to consume the Mozambique Ocean and led to the assembly of eastern Gondwana. Our new reconstruction uses true polar wander to constrain the relative paleo-longitude of Tarim, South China and West Africa. In this scenario, the closure of the Mozambique Ocean and formation of Gondwana was orthogonal to the preceding super-continent Rodinia.
... Therefore, from different tectonic discrimination diagrams, it is evident that the Borjuri diorites were emplaced in a post-collisional environment. Kennedy (1964) first introduced the term Pan-African to explain major tectono-thermal events at approximately 500 Ma, which resulted in the structural differentiation of Africa (Rino et al. 2008). Later studies showed that the Pan-African orogeny has widely contributed to the crust formation and reworking during the reconstruction of Gondwana supercontinent (Kroner and Stern 2004). ...
The Assam-Meghalaya Gneissic Complex (AMGC) of northeast India contains numerous Pan-African granitic bodies that have been attributed to post-collisional rift-related magmatism. The present study is concerned with the first appraisal of intermediate magmatism (diorite, monzonite, and monzodiorite) found in the Borjuri Pluton of Mikir Massif, which is the eastern extension of AMGC. The diorites are strongly metaluminous and exhibit enriched LREE ([La/Yb] N = 1.63-7.37) with respect to HREE ([Gd/Yb] N = 1.95-2.27). The studied rocks do not show any mineralogical or textural indication of metamorphism. Tectonic discrimination diagrams indicate that these rocks originated in a within-plate tectonic setting. The lower Mg# (33.49-38.69), low Cr (below detection limit), and Ni (27-41 ppm) contents along with elemental ratios such as Rb/Sr (0.32-0.95), La/Nb (0.49-4.21), and Nb/Ce (0.11-0.64) suggest a crustal source for the diorites. Discrimination diagrams coupled with elemental ratios suggest that these rocks originated due to partial melting of mafic components in the crust with possible contribution from mantle materials. The P-T conditions of diorite emplace-ment (7.4 kbar, 688°C) were calculated using the amphi-bole-plagioclase geothermobarometer. Geochemical and geochronological data of the Pan-African felsic plutons reported from the AMGC indicate that these rocks were emplaced in a post-collisional extensional regime. The Borjuri Pluton is in close proximity with the Kathalguri Pluton, which has been reported as a product of Pan-African magmatism. In view of the numerous extensional Pan-African felsic magmatism reported from the AMGC and based on the close vicinity of the Borjuri diorites with the Kathalguri granites, we speculate that the Borjuri diorites are products of the Pan-African post-collisional magmatism.
... Цифры в квадратах 1-4 -интрузивы: 1 -Ерудинский, 2 -Каламинский, 3 -Среднетырадинский, 4 -Гусянковский; 5 -Тейский гранитогнейсовый купол. (б) Конфигурация ядра Родинии и расположение подвижных поясов гренвильской складчатости показаны голубым цветом по Rino et al., 2008c модификацией (Ernst et al., 2008 характерно наличие крупных изометричных зерен кварца, развитых в основной массе породы как в форме отдельных выделений, так и в ассоциации с мелкозернистым агрегатом гранулированного кварца. Кварцевые сиениты отличаются от гранитов пониженным содержанием кварца и повышенным -овоидных выделений калишпата. ...
Обосновывается проявление коллизионного гранитоидного магматизма, связанного с неопротерозойским (880-860 млн лет) орогеническим событием на юго-западе Сибирского кратона. Приведены новые данные по составу, U-Pb (SHRIMP II) возрасту циркона и Sm-Nd изотопным параметрам пород Гусянковского гранитоидного массива, расположенного в Приенисейской зоне разломов Енисейского кряжа. Конкордатный U-Pb возраст циркона равен 865 ± 9 млн лет и указывает на формирование гранитоидов Гусянковского массива в середине раннего неопротерозоя, вместе с гранитоидами Каламинского и Ерудинского массивов, расположенных в Татарско-Ишимбинской системе разломов, на одном и том же этапе коллизионных событий около 880-860 млн лет. Известково-щелочные граниты, гранодиориты и лейкограниты Гусянковского массива на основании высокой глиноземистости и редкоэлементного состава отнесены к S-типу и формировались из метапелитового источника. Породы Каламинского и Ерудинского массивов по совокупности геохимических параметров отвечают низкокалиевым I-гранитам, наиболее вероятные источники которых это мафические породы и тоналиты. Гранитоиды Гусянковского массива, с одной стороны, Каламинского и Среднетырадинского, с другой, контрастно различаются по изотопному Nd составу. Источником первых были либо метапелиты тунгусикской серии, либо метаосадочные породы сухопитской серии при участии ювенильного материала. Для гранитов Каламинского и Среднетырадинского массивов допускается вклад более древней, возможно, палеопротерозойской коры и ювенильного мафического источника. Таким образом орогенные события 880-860 млн лет назад привели к генерации расплавов на различных уровнях палео-мезопротерозойской коры Заангарья Енисейского кряжа. Геодинамическая история региона сопоставляется с синхронной последовательностью и схожим стилем тектоно-термальных событий по периферии крупных докембрийских кратонов Лаврентии и Балтики, что подтверждает палеоконтинентальные реконструкции о тесных пространственно-временных связях между этими кратонами, Сибирью и их вхождении в состав Родинии.
... The assembly of Gondwana over 800 -550 Ma (Meert and Van Der Voo 1997) coincides with a crucial time in the evolution of Earth systems. Neoproterozoic lithologies provide evidence for the emergence of complex multicellular life (Shen et al. 2008), global glaciation (Shields-Zhou et al. 2016), and an important period of continental crust production in the Pan-African orogeny (Rino et al. 2008). Key to understanding these interrelated processes are paleotectonic reconstructions, which give constraints on the timing, duration, and style of magmatism. ...
The Johnston Complex represents a rare inlier of the Neoproterozoic basement of southern Britain and offers a window into the tectonomagmatic regime of East Avalonia during the assembly of Gondwana. This work presents in-situ zircon (U-Pb, Lu-Hf), apatite (U-Pb), and trace element chemistry for both minerals from the Complex. Zircon and apatite yield a coeval crystallisation age of 570 ± 3 Ma, and a minor antecrystic zircon core component is identified at 615 ± 11 Ma. Zircon Lu-Hf data imply a broadly chondritic source, comparable to Nd data from East Avalonia, and T DM ² model ages of ca. 1.5 Ga indicate source extraction during the Mesoproterozoic. Zircon trace element chemistry is consistent with an ensialic calc-alkaline continental arc setting and demonstrates that magmatism was ongoing prior to terrane dispersal at 570 Ma. Apatite trace element chemistry implies a sedimentary component within the melt consistent with voluminous S-type granite production during the formation of Gondwana. The similarity of ɛHf and geochemistry between both zircon age populations suggest derivation from a uniform source that did not undergo significant modification between 615 – 570 Ma. Time-constrained apatite-zircon chemistry addresses complexities in dating S-type granitoids (zircon inheritance) and permits inferences on post-magmatic thermal histories.
Supplementary material: https://doi.org/10.6084/m9.figshare.c.6484464
... Ga S-type zircons are probably associated with the S-type magmatism of the Grenvillian orogeny (Watt, 2001;Zhu et al., 2020;Rivers, 2021). These S-type zircons would therefore constitute a recycled component, like the recycled 480-620 Ma zircons, deposited in the Ediacaran to Ordovician strata of the South China Block and South Qinling Belt, located along the northern margin of east Gondwana (Rino et al., 2008;Cawood et al., 2007Cawood et al., , 2018. The 1.0-1.1 Ga basalts and andesites of the Shennongjia region were interpreted as part of the Grenvillian orogenic belt (Fig. 10;Qiu et al., 2011), and thus have the potential of providing unannealed-type zircons. ...
... All the terranes listed above include some zircon grains from the early Neoproterozoic ($1000 Ma), which corresponds to the global Grenvillian tectonothermal event (Rino et al., 2008). Similar ages have also been reported for zircon from the late Neoproterozoic-Ordovician sandstones of the Cathaysia block and the Cambrian-Devonian sandstones of the eastern margin of the Indochina block (central Vietnam;Fig. ...
Devonian–Carboniferous strata in the Hida Gaien belt, Southwest Japan, are characterized by a change in the dominant lithology from clastic rocks and limestones to volcanic rocks. The sandstone compositions and detrital zircon U–Pb ages indicate that the Devonian sedimentary rocks were derived from various basement rocks, including granite and basalt, that were uplifted, exposed, and eroded during the Early–Middle Devonian (398–383 Ma). The source of sediment to these strata changed to basalts and rhyolites in the early Carboniferous (∼346 Ma). Early Carboniferous bimodal volcanic rocks are present in the Hida Gaien and South Kitakami belts, the southeastern margin of the South China block (Hainan), and the Jilin area (NE China) of the eastern Central Asian Orogenic Belt (CAOB). The Cambrian–Silurian zircon grains (540–480 Ma and 460–420 Ma) in the Hida Gaien belt were derived from arc basement of a similar age to the South Kitakami and Kurosegawa belts, the Jiamusi–Khanka–Bureya (NE China and the Russian Far East) and Songliao–Xilinhot (Inner Mongolia) blocks in the eastern CAOB, and the eastern South China and Indochina blocks. The Devonian strata also contain Precambrian zircon grains derived from Mesoarchean basement (∼3000 Ma) and the Grenvillian tectonothermal event (∼1000 Ma), suggesting sediment supply from NE Gondwana (the Thomson and Lachlan orogens of eastern Australia) or related continental remnants. Detrital zircon U–Pb age spectra similar to those of the Devonian strata of the Hida Gaien belt are also observed in Silurian–Devonian metasedimentary rocks in the Jilin area. During the early Paleozoic, the Hida Gaien belt, the eastern margin of the South China block, and the magmatic arcs and microcontinents in the eastern CAOB were located close to NE Gondwana along the western margin of the Paleo-Pacific Ocean.
... The Pan-African Orogeny includes all the orogens which developed following the final Grenvillian thermotectonic events up until the creation of Gondwana. It was a global, long-term orogenic cycle (1,000-550Ma) and one of the most important periods of crustal maturation in Earth's history, including the diachronic opening and closing of large ocean realms and the accretion and collision of buoyant crustal blocks (Abdelsalam et al., 2002;Bento dos Santos et al., 2015;Collins and Pisarevsky, 2005;Ennih and Liégeois, 2008;Kroner and Stern, 2004;Murphy et al., 2013;Rino et al., 2008). ...
This work assessed the age distribution of Cadomian/Pan-African orogenic events (550-590 and 605-790Ma, respectively) in several zones of Iberian Massif by means of detrital and inherited zircon analysis compilation. Detrital zircon age spectra show that throughout the late Neoproterozoic-to-Early Ordovician era (~120Ma sedimentary record), the main systematic peak occurs at ~610Ma, followed by peaks at typical Cadomian ages (~590-550Ma). Inherited zircons incorporated in Cambrian-to-Lower Ordovician igneous rocks show typical Cadomian ages (~590-550Ma) but, once again, a remarkably consistent Pan-African ~610Ma peak occurs.
In accordance with compiled zircon data and taking into account the evidence of North African peri-cratonic inliers, Ediacaran (~610Ma) zircons incorporated in Paleozoic magmas provide indirect evidence of Pan-African magmatism, suggesting that these magmas and synorogenic sediments are likely to constitute the cryptic stratigraphic infrastructure of most of the Iberian Massif. The main source of ~610Ma inherited zircons may be the lateral chrono-equivalents of the Saghro and Bou Salda-M`Gouna Groups (Anti-Atlas, Morocco) and/or coeval igneous rocks from West African Craton or Trans-Sahara Belt, emplaced at a stratigraphic level below the late Ediacaran sediments of the Ossa Morena Zone and the Central Iberian Zone.
Assuming that the Iberian crust is a fragment of the Pan-African orogen, a relative paleoposition situated between the West African Craton and the Trans-Saharan Belt during the Late Neoproterozoic is proposed. The closed-system behaviour of Stenian-Tonian detrital zircon ages in the Trans-Sahara Belt suggests that this mega-cordillera acted as a barrier, in paleogeographic terms, to separating the Sahara Metacraton from Iberia. In Iberia, the opening of the system to Stenian-Tonian detrital zircon during the Ordovician indicates that, at that time, the Trans-Saharan Belt had already become a vast peneplain, which favoured a large drainage system with a long-distance transport mechanism that fed the passive continental margins.
... The late Neoproterozoic-Cambrian is a pivotal time interval in Earth's evolution characterized by global-scale orogenesis, rapid continental growth, profound changes in the chemistry of the oceans and atmosphere, rapid and dramatic climate swings, and an explosion in biological activity (e.g., Nance et al., 1988;Dalziel 1991Dalziel , 1997Hoffman 1991;Murphy and Nance 1991;Hoffman et al. 1998;Maruyama and Santosh 2008;Narbonne 2010;Knoll 2013;Mitchell et al., 2021;Nance, 2022). Orogenic activity involved a succession of continental collisions spanning more than 100 million years that culminated in the amalgamation of Gondwana (e.g., de Wit et al., 1988, 2008Collins and Pisarevsky, 2005;Rino et al., 2008;Abu-Alam et al. 2013), and the development of peripheral orogens that reflect arc magmatism and accretionary tectonic processes as subduction zones re-located to Gondwana's margins (e.g., Murphy and Nance, 1991;Cawood et al., 2021). ...
The late Neoproterozoic-Cambrian interval is characterized by global-scale orogenesis, rapid continental growth, and profound changes in Earth systems. Orogenic activity involved continental collisions spanning more than 100 million years, culminating in Gondwana amalgamation. Avalonia is an example of arc magmatism and accretionary tectonics as subduction zones re-located to Gondwana's periphery in the aftermath of those collisions, and its evolution provides significant constraints for global reconstructions. Comprising late Neoproterozoic (ca. 650-570 Ma) arc-related magmatic and metasedimentary rocks, Avalonia is defined as a composite terrane by its latest Ediacaran-Ordovician overstep sequence; a distinctive, siliciclastic-dominated cover bearing “Acado-Baltic” fauna. This definition implies Neoproterozoic Avalonia may consist of several terranes, and so precise paleomagnetic or provenance determination in one locality need not apply to all. On the basis of detrital zircon and Nd isotopic data, Avalonia and other lithotectonically-related terranes such as Cadomia, have long been thought to have resided along the Amazonian-West African margin of Gondwana between ∼650-500 Ma, Avalonia connected to Amazonia, and Cadomia to West Africa. These interpretations have constrained Paleozoic reconstructions; many imply the departure of several peri-Gondwanan terranes led to the Early Paleozoic development of the Rheic Ocean whose subsequent demise in the late Paleozoic led to Pangea amalgamation. Since these ideas were proposed, several new lines of evidence have challenged the Amazonian affinity of Avalonia. First, there is evidence that some Avalonian terranes may have been “peri-Baltican” during the Neoproterozoic. Baltica was originally excluded as a potential source for Avalonia because, unlike Amazonia, arc-related Neoproterozoic rocks were not documented. However, subsequent recognition of Ediacaran arc-related sequences in the Timanides of northeastern Baltica invalidates this assumption. Second, detailed paleontological and lithostratigraphic studies have been interpreted to reflect an insular Avalonia, well removed from either Gondwana or Baltica during the Ediacaran and early Cambrian. Third, recent paleomagnetic data have raised the possibility of an ocean (Clymene Ocean) between Amazonia and West Africa in the late Neoproterozoic, thereby challenging conventional reconstructions that show the “peri-Gondwanan” terranes as a contiguous belt straddling the suture zone between these cratons. In this contribution, we critically re-evaluate the provenance of the so-called “peri-Gondwanan” terranes, the contiguity of the so-called “Avalonian-Cadomian” belt, and the validity of the various plate tectonic models based on the traditional interpretation of these terranes. In addition, we draw attention to critical uncertainties and the challenges that lie ahead.
... The detrital zircon age spectra of the Chivillas Formation show three main age populations: Meso-Neoproterozoic, Carboniferous-Triassic, and Early Cretaceous ( Figure 6) The Meso-Neoproterozoic population (1400-910 Ma) is present in all studied samples and is characteristic of the Grenville Orogeny (e.g. Rino et al. 2008;Dickinson and Gehrels 2009a). Most zircon grains in this age range indeed have metamorphic features and could have been derived from the high-grade metamorphic rocks of the Oaxacan Complex (e.g. ...
Sandstone petrography, zircon and apatite U-Pb geochronology, and apatite geochemistry of Early Cretaceous siliciclastic turbidites interbedded with basalt (Chivillas Formation) in the southern Sierra Madre Oriental, Mexico, indicate local provenance from westerly basement sources. Three main detrital populations were observed in both the zircon and apatite geochronology: Meso–Neoproterozoic, Carboniferous–Permian, and Early Cretaceous. Apatite Sr/Y vs light rare earth element discrimination diagrams indicate that most Precambrian grains have affinity with high-grade metamorphic rocks and most Phanerozoic grains with igneous rocks. These results are consistent with derivation from exposed crystalline sources within the Acatlán-Oaxacan block including the Grenvillian Oaxacan Complex, the East Mexico Arc, and the Early Cretaceous continental arc. The compositional disparities observed in individual samples reflect differences in source of individual turbiditic flows comprising the Chivillas Formation. We surmise that various rivers from the northern and southern Acatlán-Oaxacan block drained into the basin during the Early Cretaceous. Furthermore, detrital apatite fission-track analyses of Chivillas sandstones yielded mostly 42–40 Ma ages (Eocene) that post-date the shortening of the Mexican orogen in the southern Sierra Madre Oriental. Thermal models calculated based on track lengths indicate rapid exhumation of Chivillas rocks at 46–36 Ma, which is the time of the development of the Tehuacán Valley and reactivation of the Oaxaca Fault System as a normal fault.
... Gravelotte emeralds have been shown to have geochemical signatures consistent with an S-type granite protolith (Alonso-Perez and Day, 2021). Their association with the Pan-African metamorphic belt and other emeralds with similar compositions in Zambia and Madagascar may indicate that they date to only ∼900 to 600 Ma (Rino et al., 2008). To determine if Gravelotte emeralds are indeed Archean in age, we report Rb-Sr isotope systematics and trace element abundances for them, as well as for the younger Muzo deposit in Colombia. ...
New 87Rb-87Sr data are reported for emeralds from Gravelotte, South Africa and Muzo, Colombia, the first such data in 30 years. The Gravelotte deposit is inferred to be the world's oldest emerald deposit from the ∼2.97 Ga U-Pb age of the associated pegmatite. The majority of Gravelotte emeralds plot on an 87Rb-87Sr errorchron with an age of 2883 ± 131 Ma, close to the pegmatite age, demonstrating that the emeralds are Mesoarchean in age. The Muzo emerald data, when combined with data from nearby Colombian emerald deposits, define an age of ∼48 Ma, younger than muscovite Ar-Ar ages (65-62 Ma), likely reflecting the resetting of 87Rb-87Sr in some emeralds. The initial Sr isotopic composition for Gravelotte emeralds is radiogenic (87Sr/86Sri = 0.841), and their trace element signatures support their formation from a mature, high Rb/Sr, felsic continental crustal protolith in the Mesoarchean. Direct 87Rb-87Sr dating of emeralds holds promise for offering constraints on both mineralisation ages and source compositions. © 2022 European Association of Geochemistry. All rights reserved.
... Положение Сибирского кратона, по [Zhao et al., 2004]. б -конфигурация ядра Родинии и расположение подвижных поясов гренвильской складчатости показаны голубым цветом, по [Rino et al., 2008] [Dalziel, 1997;Torsvik, 2003]; Акитканского (Сибирь) и Телон-Талсон (Лаврентия) магматических поясов (голубым цветом), по [Pisarevsky et al., 2008]. ...
... Considering the consistent distribution of coeval arc-derived magmatic formations along the southern margin of the Mongol-Okhotsk Belt, the oceanic basin was closed in a relatively simultaneous manner. The growth of the continental crust has represented one of the most exciting debates in the Earth Sciences for at least the last three decades (e.g., Belousova et al., 2010;Ganbat, Tsujimori, Boniface, et al., 2021;Jahn et al., 2000;Kemp et al., 2007;Kröner et al., 2014Kröner et al., , 2017Rino et al., 2008;Taylor & McLennan, 1985). Pioneering research pointed out that the formation of continental crust was episodical and most of its volume formed in the Precambrian (e.g., Armstrong, 1981). ...
The Mongol–Okhotsk Belt, the youngest segment of Central Asian Orogenic Belt, was formed by the evolution and closure of the Mongol–Okhotsk Ocean. The oceanic closure formed two volcanoplutonic belts: Selenge Belt in the north and the Middle Gobi Belt in the south (in present day coordinates). However, the origin and tectonic evolution of the Mongol–Okhotsk Belt in general, and the origin and formation age of the Middle Gobi Belt in particular, remain enigmatic. To better understand the history of the magmatic activity in the Middle Gobi Belt, we conducted geochemical, U–Pb geochronological, zircon Hf, and whole‐rock Nd isotopic analyses of samples from the Mandalgovi volcanoplutonic suite, the major component of the Middle Gobi Belt. Our results show that the plutonic rock consists of ~285 Ma gabbro, ~265 Ma biotite‐granite; ~250 Ma hornblende‐granodiorite. The volcanic counterpart is represented by a Permian Sahalyn gol rhyolite and ~ 247 Ma Ikh khad andesite. The geochemical compositions of biotite‐granite and hornblende‐granodiorite indicate that their precursors were metagraywacke and amphibolite, respectively. They are characterized by positive whole‐rock εNd(t) and zircon εHf(t) values, indicating juvenile protoliths. The gabbro was derived by partial melting of a metasomatized lithospheric mantle source in a supra‐subduction setting. The biotite‐granite and Sahalyn gol rhyolite are formed by remelting of sediments in an inter‐arc extension setting. Later the hornblende‐granite and Ikh khad volcanic were emplaced at a volcanic arc formed by the subduction of the Mongol–Okhotsk Ocean. We conclude that the magmatic rocks of the Middle Gobi Belt formed in an active continental margin setting. Considering the consistent distribution of coeval arc‐derived magmatic formations along the southern margin of the Mongol–Okhotsk Belt, the oceanic basin was closed in a relatively simultaneous manner.
... This process involved several orogenic events and is known as the protracted Pan-African/ Brasiliano Orogeny, which extended up to the Cambrian (e.g. Kröner 1984;Rino et al. 2008). From a global perspective, the late Neoproterozoic to Cambrian assembly of Gondwana was the result of the convergence that followed the early Neoproterozoic Rodinia break-up (e.g. ...
Some recent models challenge the position and extension of the assumed oceanic basins formed through the break-up of Rodinia, and the tectonic processes involved in the Gondwana assembly, making the investigation of the Early Neoproterozoic
record of great relevance. Within the South-American Atlantic margin, the Punta del Este Terrane (PET) of the Dom Feliciano Belt (DFB) comprises a unique Tonian to Ediacaran record, and has a strategic position to reconstruct spatio-temporal relationships with the southern African orogenic belts. Novel zircon U–Pb and Lu–Hf data from the PET orthogneissic basement display Tonian magmatic ages (805–760 Ma) and Hf isotopic signatures indicative of mainly crustal/metasedimentary sources, (Nd TDM ages: 2.2–1.9 Ga, and εHf(t): − 12 to − 4). The basement paragneisses yielded late Paleoproterozoic to Neoproterozoic U–Pb ages, but dominantly positive εHf(t) values. The presented results confirm the correlation of the PET with the Coastal Terrane of the Kaoko Belt, and discard the idea of the Nico Pérez Terrane as a source. Detrital zircon U–Pb and Lu–Hf data from the Rocha Formation yielded a main peak at ca. 660 Ma, with the Neoproterozoic grains showing a εHf(t) between + 1 and + 14. The deposition age of the Rocha Formation is constrained by the youngest detrital zircon age peak (660 Ma), and the beginning of the deposition of the Sierra de Aguirre Formation (580 Ma). The data indicate common sources with the Marmora Terrane, and it is thus proposed that the Rocha Formation belongs to the Gariep Belt, and it was juxtaposed during the late Ediacaran to the DFB.
... Between 1140 and 900 Ma, the EEC was incorporated into the Rodinia supercontinent, marked by the Sveconorwegian orogeny (Bogdanova et al., 2008). On the other hand, the crustal blocks of the southern and western parts of Europe include terranes that were formed on the northern margin of the supercontinent Gondwana, which originated as a result of the dispersal of Rodinia and associated Late Neoproterozoic collisional events that culminated at ca. 800-600 Ma in the Pan-African Orogeny (Rino et al., 2008). ...
With the aim of testing the representativity of detrital zircon U-Pb datasets, we combine new and published data from 31 large river systems in Europe and compare this information with the well-known geology of the continent. Detrital zircon ages range from Archean to Cenozoic and age clusters can be linked to different orogenic cycles and the formation of supercontinents thus representing all relevant geological events in Europe at the continental scale. The Variscan Orogen is the largest episode of crustal reworking in Europe and consequently Variscan detrital zircons occur in all rivers. Other important age clusters are the Alpine 40–25 Ma, post-Alpine 10–0.2 Ma, the Caledonian 490–400 Ma, and the Avalonian-Cadomian 650–540 Ma. Detrital zircons of 1170–930 Ma and 1700–1400 Ma are significant in Scandinavia, as well as 2900–2500 Ma and ca. 1850 Ma in east Europe.
Although the observed distribution of U-Pb detrital zircon ages is qualitatively representative of the geology of Europe at the continental scale, it is not always the case at the basin scale. Importantly, quantitative representativity for both, basin and continental scales, is not achieved. Variable zircon fertility and the sand generation potential of different lithologies highly bias the U-Pb age distributions. For instance, the magma poor Alpine orogen is relevant in minor age clusters in the Po and Danube rivers, but not in rivers draining to the west and north of the Alps, such as the Rhone and Rhine. Similarly, detrital zircons in the range of 10–0.2 Ma occur only in sediments from the Garonne and Loire rivers, although the Cenozoic igneous provinces are widespread in Europe. Detrital zircons from the post-Variscan Permian rocks were mostly found in the Po and Glomma rivers, where Permian granitoids are more abundant than volcanics of this age. Other natural causes of bias, such as transport and recycling can be identified base on the analyses of size and shape of detrital zircons. In the case of west Europe, our data shows that U-Pb detrital zircon patterns and zircon shape are mainly affected by recycling. Moreover, we tested corrections to the U-Pb age distribution for each river basin based on simple geomorphological parameters obtained from Digital Elevation Models. This attempt to overcome the overrepresentation of certain source regions resulted in a considerable change in age peak proportions towards a better quantitative representativity. However, full representativity seems unachievable, even in studies of modern sedimentary systems with known geology.
... Paleozoic metasedimentary rocks exposed in the Pyrenees record complex geochronological signatures inherited from Gondwanan margin tectonics, which are reflected by (1) Neoproterozoic Pan-African (>850-600 Ma) ages initially derived from rock assemblages associated with Trans-Saharan Belt granites and metamorphic rocks formed during the closure of the Mozambique Ocean and East African Orogeny (Abdeen & Greiling, 2005;Rino et al., 2008). (2) Basement rocks in the Axial Zone preserve metamorphic and magmatic geochronologic signatures from the Ediacaran to Cambrian Cadomian orogeny (600-520 Ma) that are related to the subduction of the Iapetus Oceanic crust below Gondwana, which drove continental magmatism and subsequent metamorphism associated with shortening (Álvaro et al., 2008;Linnemann et al., 2008). ...
The Pyrenees Mountains are a classic example of a doubly‐verging collisional orogenic system with flanking retro‐ and pro‐foreland basin systems. Previous bedrock and detrital geo‐/thermochronologic studies have observed magmatic and exhumational related ages that reflect a complex thermo‐tectonic evolution of the European and Iberian plate margins related to break‐up and assembly of the Gondwana, Pangea, and Pyrenean‐Alpine orogenic cycles. This study integrates detrital zircon, rutile, and apatite U‐Pb dating and, detrital zircon and apatite (U‐Th)/He dating from modern river sands from the northern and southern Pyrenees, with PECUBE thermokinematic modeling of bedrock cooling ages to simulate detrital age distributions in order to evaluate: (1) regional patterns in long‐term crustal processes associated with pre‐Pyrenean crustal shortening, crustal thinning, and magmatism along the Iberian and European plate margin; (2) timing of regional cooling and inferred erosion related to Pyrenean orogenesis; and (3) the exhumation processes associated with post‐orogenic decay and erosion. Modern river multi‐mineral detrital geo‐/thermochronometry results are consistent with previous bedrock thermal history models and records punctuated Variscan and Pyrenean cooling events in the pro‐wedge that contrasts with protracted Permian to Pliocene thermal history preserved in the retro‐wedge. Detrital age distributions from PECUBE modeling predict the Pyrenean age component in both detrital apatite and zircon (U‐Th)/He age distributions, indicating the modeled exhumation patterns in the Axial Zone and Northern Pyrenean Zone can predict observed Pyrenean thermochronology ages. The presence of strong Pyrenean age peaks among the modern river sand and modeled detrital cooling age distributions suggest retro‐wedge deformation and exhumation remained active during the main phase of pro‐wedge activity and experienced significant orogenic decay. Isolated Miocene apatite He ages from the North Pyrenees modern river record post‐orogenic cooling, due to tectonic mode switch to extension and (or) climate driven enhanced exhumation.
... The Pan-African orogeny has been divided into two parts, namely ca. 900-630 Ma which is characterized by terrane accretion as seen in the Arabian-Nubian shield, and 630-540 Ma which shows collision and escape-tectonics in many parts of East African orogen (Rogers and Santosh, 2002;Kroner and Stern, 2005;Rino et al., 2008). ...
The Aravalli-Delhi Mobile Belt (ADMB) in the northwestern part of the Indian Shield represents the final stage of a complex tectonic evolution witnessed by the recognition of three distinct orogenies that have resulted in northwestward accretion of the terranes belonging to Archaean to Neoproterozoic ages. In this contribution, a review of the deformation structures of different terranes is discussed with their tectonic implications and global correlation with other supercontinent assemblies. In the west, the NE-SW trending Neoproterozoic South Delhi terrane is marked by coaxial folding between DF1 and DF2 along the NE-SW axis and cross folded by DF3 folds in the NW-SE axis. Several meso- to large-scale DF2 thrusts and DF4 fractures occur in the belt, that acted as channels for the exhumation of granulite and basement gneisses. Excess shortening led to orogen parallel extension and lateral escape of the material that reactivated the DF2 thrusts as strike-slip faults. Based on the ages of syn-DF1 granite gneisses -DF4 fractures, the South Delhi orogeny has been constrained between 0.87 and 0.6 Ga. The Paleoproterozoic North Delhi Terrane is marked by a coaxial folding between NF1 and NF2 folds and later cross-folded by NW-SE trending NF3 folds, producing dome- and- basin structures. Age of syntectonic granite and late-stage metamorphism constrain the north Delhi orogeny between 1.8 and 0.96 Ga. The Paleoproterozoic Aravalli Terrane is divided into a shallow-marine eastern and deeper marine western part by the Rakhabdev suture zone. The entire assemblages were folded by NE-SW isoclinal and recumbent AF1 folds which, with progressive deformation were reoriented to E-W axial trend. The AF2 is upright and NE-SW trending. The AF3 folds are E-W to NW-SE trending and have produced type 1 and type 2 interference patterns, with AF2 and AF1 respectively. Age of syn-AF1 migmatisation in the northern part and syn- AF3 granites in the south constrain the Aravalli orogeny between 1.7 and 0.96 Ga, coeval with the North Delhi orogeny. The granulite and charnockite were tectonically emplaced within Sandmata Complex during the Aravalli orogeny. The Archean Bhilwara terrane produced from Bhilwara orogeny marks the stabilisation of the crust in NW India by the intrusion of Berach and equivalent granites at 2.6 Ga. The terrane is divided into Sandmata and Mangalwar complexes that consist of migmatite gneisses with greenstone slivers. Several Neoarchean to Paleoproterozoic volcano-sedimentary schist belts were tectonically interleaved within Mangalwar Complex. The migmatitic rocks of the terrane show flow folding in various directions while the schist belts are characterized by extremely appressed NE-SW trending reclined folds (BF1 and BF2), inverted BF2 folds, E-W open BF3 folds, and multiple strike-slip shear zones and thrusts. The ADMB exhibits a syntaxial bend in the eastern part attributed to indentation tectonics by Berach granite during syn- South Delhi orogeny. The Aravalli orogeny is correlatable with Nuna and South Delhi with Pan- African orogeny that gave rise to Columbia and Gondwanaland Supercontinent assembly respectively. The Grenville orogeny has thermal rejuvenation in Aravalli and Bhilwara terranes.
... The formation of felsic and buoyant continental crust is particular to Earth in the solar system (Christensen and Mooney, 1995;Cawood et al., 2013), otherwise, the planet would have become an insipid globe enveloped by a dense basaltic crust and covered by a global ocean with no chemically evolved continental crust (Patchett and Bridgwater, 1984;Arndt, 2013). The study of the processes through and rates at which continental crust has grown through time is a fundamental focus of earth science research (e.g., Rino et al., 2004Rino et al., , 2008Stern, 2008Stern, , 2011Condie and Aster, 2010;Hawkesworth et al., 2010;Nance et al., 2014;Spencer et al., 2017). The preserved crustal record is dependent on the balance between the volume of new crust extracted from the mantle by magmatic processes and the volume recycled back into the mantle by tectonic erosion and lower-crustal delamination (Spencer et al., 2017). ...
The crustal growth and reworking processes of accretionary orogen such as the Central Asian Orogenic Belt (CAOB) have been a controversial issue. Here, we present in situ zircon U–Pb and Lu–Hf isotopic data for granitoids from a microcontinent (the Songnen Massif) and an arc terrane (the Duobaoshan arc terrane), which generally represent two main crustal components in the eastern CAOB to establish a crustal growth model for an accretionary orogen and to trace the influence of the assembly and breakup of supercontinents on crustal evolution in an accretionary orogen. Neoproterozoic–Mesozoic granitoids distributed in the Songnen Massif show a step-like crustal growth pattern over time with three major periods of development: Paleoproterozoic crustal growth at 2.2–1.8 Ga, Mesoproterozoic growth at 1.6–1.0 Ga, and a third pulse of growth at 0.85–0.6 Ga, along with two short pauses at 1.8–1.6 Ga and 1.0–0.85 Ga. The assembly and collision phases of supercontinents corresponded to the enhanced and degressive crustal growth rates of the Songnen Massif, respectively, suggesting that the supercontinent cycles are responsible for the episodic crustal growth pattern in the region. Crustal reworking of the Songnen Massif occurred during 1000–180 Ma, with a fluctuation at 800–600 Ma, which provided a major contribution to the isotopic heterogeneity of lower continental crust. Isotopic compositions of granitoids from the Duobaoshan arc terrane located between the Xing'an and Songnen massifs, together with those of granitoids from other microcontinents, suggest that most of the continental crust beneath the microcontinents in the eastern CAOB generated during the Precambrian, whereas a significant amount of lateral crustal accretion occurred in continental arc settings during orogenies and amalgamation of microcontinents during the Phanerozoic.
... Reconstructing their provenance is often done analysing the age spectra of detrital zircon grains. Recently, the number of such studies increased significantly in Namibia and adjacent areas (Gärtner et al. 2014;Garzanti et al. 2014aGarzanti et al. , b, 2017aIizuka et al. 2013;Klama 2008;Rino et al. 2008;van der Westhuizen 2012;Vermeesch and Garzanti 2015;Vermeesch et al. 2010). However, most of the studies are restricted to the Orange River system and coastal deposits, while only a minor number of samples were taken from other rivers or dunes (Gärtner et al. 2014;Garzanti et al. 2017b;Vermeesch et al. 2010). ...
Extensive morphological and age studies on more than 4600 detrital zircon grains recovered from modern sands of Namibia reveal complex mechanisms of sediment transport. These data are further supplemented by a zircon age database containing more than 100,000 single grain analyses from the entire southern Africa and allow for hypothesising of a large Southern Namibian Sediment Vortex located between the Damara Orogen and the Orange River in southern Namibia. The results of this study also allow assuming a modified model of the Orange River sand highway, whose origin is likely located further south than previously expected. Moreover, studied samples from other parts of Namibia give first insights into sediment movements towards the interior of the continent and highlight the potential impact of very little spatial variations of erosion rates. Finally, this study points out the huge potential of detrital zircon morphology and large geo-databases as an easy-to-use additional tool for provenance analysis.
... The Neoproterozoic Era witnessed global continental reorganization, resulting in the two major supercontinental assemblies of Rodinia ( Fig. 1a; through the Grenvillian Orogeny) and Gondwana (Fig. 1b; through the Pan-African Orogeny) (Collins & Pisarevsky, 2005;Li et al. 2008;Rino et al. 2008;Bradley, 2011;Cawood et al. 2013;Arora et al. 2020). Meso-to Neoproterozoic amalgamation of Rodinia took place between 1100 and 900 Ma (Kröner & Cordani, 2003;Li et al. 2008;Gregory et al. 2009;Cawood et al. 2013;Jing et al. 2020), and it eventually broke apart during 750-720 Ma (Fig. 1a) (Gregory et al. 2009;Jing et al. 2020). ...
Fragmentation and amalgamation of supercontinents play an important role in shaping our planet. The break-up of such a widely studied supercontinent, Rodinia, has been well documented from several parts of India, especially the northwestern and eastern sector. Interestingly, being located very close to the Proterozoic tectonic margin, northeastern India is expected to have had a significant role in Neoproterozoic geodynamics, but this aspect has still not been thoroughly studied. We therefore investigate a poorly studied NE–SW-trending Shillong Basin of Meghalaya from NE India, which preserves the stratigraphic record and structural evolution spanning the Neoproterozoic Era. The low-grade metasedimentary rocks of Shillong Basin unconformably overlie the high-grade Archean–Proterozoic basement and comprise a c. 4000-m-thick platform sedimentary rock succession. In this study, we divide this succession into three formations: lower Tarso, middle Ingsaw and upper Umlapher. A NW–SE-aligned compression event later caused the thrusting of these sedimentary rocks over the basement with a tectonic contact in the western margin, resulting in NE–SW-trending fold belts. The rift-controlled Shillong Basin shows a comparable Neoproterozoic evolution with the equivalent basins of peninsular India and eastern Gondwana. The recorded Neoproterozoic rift tectonics are likely associated with Rodinia’s break-up and continent dispersion, which finally ended with the oblique collision of India with Australia and the intrusion of Cambrian granitoids during the Pan-African Orogeny, contributing to the assembly of Gondwana. This contribution is the first to present a complete litho-structural evolution of the Shillong Basin in relation to regional and global geodynamic settings.
... The Rodinia supercontinent was amalgamated in the Neoproterozoic due to amalgamation of various continents at ca.1 Ga, and fragmented at ca. 800-700 Ma (Pisarevsky et al., 2003;Wingate and Giddings, 2000) into northern and southern segments (Fig. 17a-b). The breakup of Rodinia ultimately led to assembly of Gondwana at ca. 650-530 Ma (Rino et al., 2008) along the northern edge of which the peri-Gondwanan terranes were distributed into two main segments (Murphy et al., 2004). The first comprises terranes with juvenile sources and Nd model ages of 1.3 to 1.0 Ga that include the west and east Avalonia, Carolinia, Moravia, Silesia, Oaxaqiua, and Curtis blocks. ...
Late Neoproterozoic–Early Paleozoic basement in Iran mainly comprises granites and mafic rocks locally affected by high-grade metamorphism. In this contribution, we collate whole rock chemical data for more than 600 samples; Sr–Nd isotope data for 200 samples; and zircon U-Pb ages of > 2500 grains. On the basis of zircon U-Pb ages, Iranian basement spans 570–530 Ma. The mafic rocks are tholeiitic and the felsic (granitic) rocks show affinities for predominantly I-and S-type granite with minor A-type granite. Sr-Nd isotope ratios show two discrete sources for the basement rocks. The mafic rocks yield younger Nd model ages (TDM < 1.0 Ga) and lack old zircon grains (mainly less than 800 Ma) confirming a juvenile mantle source. Conversely, the felsic rocks have older TDM ages (2.5 to 1.6 Ga) similar to inherited zircon ²³⁸U-²⁰⁶Pb ages (2.5 Ga to 650 Ma), which reflects recycling of old (Late Archean-Early Proterozoic) continental crust in the generation of felsic melts in the Late Neoproterozoic. Based in part on a recent study of Late Neoproterozoic Gondwana evolution, long-lived Proto-Tethys subduction beneath northern Gondwana (Hun terranes) may have caused: (1) Proto-Tethys slab avalanche in the lower mantle; (2) subsequent triggering of mantle plume emplacement; and (3) the calving off of a ribbon of Hun terranes from northern Gondwana. That Iran was far from the Cadomian orogeny is supported by the fact that ‘Cadomian’ terranes of Iran show evidence of having formed in an extensional tectonic regime as opposed to that of a subduction zone as for Cadomian basement in Europe. Hence, the common-use of Cadomian basement to explain Ediacaran–Cambrian magmatism in Iran is a misinterpretation. This misconception stems largely from an erroneous correlation of Iran with North America and Europe, as opposed to correlation with Central and Eastern Asia such as microcontinents in the Tibetan Plateau.
... The Homrit Akarem granitic intrusion (HAGI) outcrops in the southern part of the Eastern Desert of Egypt, the northwestern corner of the Arabian-Nubian Shield (ANS). The ANS is a large tract of juvenile continental crust (Meert, 2003;Johnson, 2003;Stoeser and Frost, 2006;Ali et al., 2010) that formed in Neoproterozoic time (850-590 Ma) upon collision between East and West Gondwana during the extensive Pan-African orogeny (Stern, 1994;Rino et al., 2008). The ANS formed mostly by accretion of oceanic island-arc terranes that developed within or on the margins of the Mozambique Ocean between ~1000 and 640 Ma (Hargrove et al., 2006;Be'eri-Shlevin et al., 2009Liégeois and Stern, 2010;Ali et al., 2010;Johnson et al., 2013), followed by extensive and voluminous intrusion and eruption of post-collisional magmatic series. ...
The Homrit Akarem granitic intrusion (HAGI) outcrops near the western edge of the south Eastern Desert basement exposure in Egypt. It is a composite of two cogenetic intrusive bodies: an early albite granite phase shallowly emplaced at the apex of a magmatic cupola, and a later subjacent pink granite phase with a marginal zone of muscovite granite and better preservation of magmatic features. Mineral chemistry of primary biotite and garnet, together with whole-rock chemistry, identify the HAGI as a highly fractionated A-type peraluminous intrusion. The chemistry of F-dominant, Li-bearing, Fe³⁺-rich primary magmatic mica in the pink granite resembles that typically found in highly evolved Nb-Y-F pegmatites. The HAGI is the evolved product of a primary magma generated by partial melting of juvenile crust of the Arabian-Nubian Shield (ANS), emplaced along a regional strike-slip fault system that promoted its ascent. The main emplacement mechanism and evolutionary sequence of the HAGI was magmatic, although secondary minerals and textures resulting from hydrothermal fluid interactions are observed, especially at its margins. Primary columbite-(Mn) crystallized from melt and was partly replaced by secondary fluorcalciomicrolite. The high fluorine content of magmatic fluids exsolved from the intrusion is indicated by quartz-fluorite veins, greisenization, albitization, and F-bearing secondary oxide minerals. The magmatic derivation of this fluid is demonstrated by the F-dominant primary mica, a siderophyllite-polylithionite solid solution commonly known as zinnwaldite. The chemistry of zinnwaldite constrains the F/OH activity ratio and oxygen fugacity of its parental melt and thereby resolves the ambiguity between pressure and the effects of F in controlling the normative quartz content of rare-metal granites. The HAGI is less mineralized than the post-collisional rare-metal granites found further east in the south Eastern Desert, replicating a trend observed previously in the central Eastern Desert and suggesting that east-west zoning in rare metal enrichment is a persistent feature across latitudes at the western edge of the ANS.
... The Eppawala carbonatites in Sri Lanka occur within the Pan-African orogenic belt (Rino et al., 2008) and have several unique features that distinguish them from similar bodies elsewhere in the world. They are not associated with alkaline silicate igneous rocks but do contain appreciable quantities of apatite-bound chlorine and spinel, whereas pyrochlore is absent (e.g. ...
Although mantle origin of carbonatites has long been advocated, a few carbonatite bodies with crustal fingerprints have been identified. The Eppawala carbonatites in Sri Lanka are more similar to orogenic carbonatites than those formed in stable cratons and within plate rifts. They occur within the Pan-African orogenic belt and have a formation age of ca. 475 Ma newly obtained in this study with no contemporary mantle-related magmatism. These carbonatites have higher (87Sr/86Sr)i ratios (0.70479 to 0.70524) and more enriched Nd and Hf isotopic compositions than carbonatites reported in other parts of the world. Model ages (1.3 to 2.0 Ga) of both Nd and Hf isotopes (apatite ɛNd(t) = -9.2 to -4.7; rutile εHf(t) = -22.0 to -8.02) are in the age range of metamorphic basement in Sri Lanka, and the carbon and oxygen isotopic compositions (δ13CPDB = -2.36 to -1.71; δ18OSMOW = 13.91 to 15.13) lie between those of mantle-derived carbonatites and marble. These crustal signatures are compatible with the chemistry of accessory minerals in the carbonatites, such as Ni-free olivine and Al- and Cr-poor rutile. Modeling results demonstrate that the Eppawala carbonatite magmas originated from a mixture of basement gneisses and marbles, likely during regional metamorphism. This interpretation is supported by the occurrence of the carbonatites along, or near, the axes of synforms and antiforms where granitic gneiss and marble are exposed. Therefore, we propose that the Eppawala carbonatites constitute another rare example of a carbonatitic magma that was derived from melting a sedimentary carbonate protolith. Our findings suggest that other orogenic carbonatites with similar features should be reexamined to reevaluate their origin.
Studies of the geological history of the Yenisei Ridge are important not only for understanding the tectonic evolution of mobile belts at the boundaries of ancient cratons but also for problem solving whether the Siberian craton was a part of the Rodinia supercontinent. The mineralogical-petrological, geochemical and isotope-geochronological studies yielded new data on the petrogeochemical composition, petrogenesis features, U-Pb age of zircon, and Sr and ¹⁴⁷ Sm- ¹⁴³ Nd isotopic parameters for the rocks of the Ryazanovsky granitoid massif located near the Yenisei fault zone of the Yenisei Ridge. These rocks are represented by high-ferruginous peraluminous varieties and are comparable to A-granites or highly differentiated I-granites. Their composition evolves from normal to subalkaline granites and leucogranites, characterized by increased concentrations of highly charged and radioactive elements. Isotopic (Sr, Nd) characteristics of the rocks indicate generation from an ancient crustal substrate, the average age of which corresponds to the Paleoproterozoic. The formation of these granites at the Meso-Neoproterozoic boundary (1013±9.9 Ma) corresponds to the early stage of the Grenville orogeny and the formation time of the structure of the Rodinia supercontinent. This episode of regional crustal evolution is correlated with the synchronous successions and similar style of tectonothermal events on the periphery of large Precambrian cratons (Laurentia and Baltica), thus confirming the reliability of the proposed paleocontinental reconstructions of incorporation of the Siberian craton into the Rodinia.
The gneisses of the Sarwar-Junia Fault Zone (SJFZ), in the Mangalwar Gneissic Complex, a part of the Banded Gneissic Complex (BGC-II) of northwest India recorded two phases of metamorphism. The pelitic gneiss from SJFZ mainly consists of biotite, sillimanite, garnet, quartz, K-feldspar and plagioclase. On the other hand, the granitic gneiss from SJFZ mainly consists of quartz, plagioclase, K-feldspar and biotite. From zircon and monazite geochronology, the protolith of pelitic gneiss was deposited on basement granitic gneiss and the metamorphism occurred at ca. 950 Ma affecting both the granitic gneiss and the pelitic gneiss. Estimation of the P-T conditions of metamorphism and pseudosection modelling of the pelitic gneiss revealed that the peak stage metamorphic condition of M2 culminated at ~850°C and ~7 kbar pressure followed by a near-isobaric cooling. Large garnet porphyroblasts in contact with retrograde biotite shows Fe-Mg resetting close to the core region, which implies a slow cooling. Therefore, the possible exhumation during the subduction-collision tectonics was very slow, if not completely ceased, at ca. 950 Ma. The shared tectonothermal history of the Sandmata Metamorphic Complex and Mangalwar Metamorphic Complex in the BGC-II is now evident from the present study of the SJFZ, and confirms the presence of Grenvillian-aged tectonothermal events in the eastern part of BGC-II. The abovementioned near-isobarically cooled and hydrated crust of the SJFZ records subsequent event(s) of shallow crustal brittle faulting as evident by the presence of pseudotachylyte veins and cataclastic fabric observed in the studied gneisses. Brittle faulting possibly occurred between ca. 905 Ma and ca. 750 Ma, as interpreted from the present geochronological data.
New detrital zircon ages from biostratigraphically well-controlled Ordovician sandstones in southeast Australia are compared with published counterparts in southern Zealandia. During Rodinia supercontinent assembly (RA), Australia and Zealandia age patterns are similar, everywhere with ubiquitous late Mesoproterozoic magmatic zircon sources. However, during earliest Gondwana supercontinent assembly (GA), the age patterns have different sediment sources: (1) those of late Neoproterozoic age are more strongly represented in Zealandia but of uncertain location, but (2) those of late Cambrian-Ordovician age are more prominent in eastern Australia, having probable origins in the Ross-Delamerian Orogen. In particular, a distinctive zircon component, ca. 600–650 Ma, is ubiquitous in Zealandia but rare in Australia. Early Paleoproterozoic and Archean (Nuna, NU) zircon sources (2000–3200 Ma) become important (and locally up to 25% total) in Zealandia but not in Australia. It is difficult to reconcile all these sediment source requirements within disparate and distant Australian-Antarctic Precambrian complexes. Instead, it is proposed that, through the early Palaeozoic, Zealandia had only local sediment sources in a discrete Rodinia basement continental block outcropping in South Zealandia that was formerly adjacent to South China.
Understanding the tectonic evolution of the Yenisei Range offers important clues not only for the tectonic evolution of orogenic belts at margins of ancient cratons but also for solving the problem of the incorporation of the Siberian craton into the Rodinia supercontinent. Results of mineralogical−petrological, geochemical, and isotope–geochemical studies provide an insight into the petrogenesis, geotectonic settings, thermodynamic parameters of formation, and the ages of the metamorphism and protoliths for the contrastingly compositionally different rocks of the Garevka metamorphic complex. The paper discusses the possible models for the origin of the rock complexes and the geodynamic settings in which they were formed. The western margin of the Siberian craton was determined to have been affected by two pulses of Neoproterozoic endogenic activity, which were related to the origin of the Rodinia supercontinent (930–900 and 880–845 Ma), and which correlated with Grenville and post-Grenville processes responsible for Valhalla folding. The
regional geodynamic history is correlated with the coeval sequence and similar style of tectono−thermal events in the peripheries of the large Precambrian cratons Laurentia and Baltica, which is consistent with the proposed Neoproterozoic paleogeographic reconstructions of close spatiotemporal relationships between these cratons and their incorporation into Rodinia configuration.
The late Paleozoic is a period of pronounced climatic and tectonic change, characterized by the onset and disappearance of continental-scale glaciers across polar Gondwana, the formation of Pangea, and widespread large igneous province volcanism. The low-latitude equatorial tropics are assumed to be places of persistent warm and wet climatic conditions throughout the Phanerozoic, which through intense silicate weathering, exert a major influence on Earth’s climate via the consumption of atmospheric carbon through carbonic hydrolytic weathering, formation of clay minerals and deliverability of alkalinity to ocean basins. Here we investigate the late Paleozoic sedimentary record of the Eastern Shelf of the Midland Basin in order to refine the climatic and provenance record of this region. The Eastern Shelf of the Midland Basin was situated within the equatorial tropics throughout the late Paleozoic and was connected to the open ocean through a network of fluvial systems that drained into the marine Midland Basin. We present new U-Pb zircon geochronology (19 samples, 2591 analyses) and sedimentary petrography (11 samples, 5800 grain counts), which we integrate with previously published paleobotany, paleosol chemistry and clay mineralogy to provide a holistic climate and tectonic record from this region. We observe major changes in sedimentary processes that we attribute to the formation of Pangea, eustatic changes linked to a dynamic high-latitude glaciation and teleconnections with low latitude hydrology, and a long-term shift in the Earth climate system all of which result in a dynamic sediment provenance history. Late Pennsylvanian and earliest Permian deposits are enriched in zircons with local affinity and interpreted to reflect local uplift and repeat incision across the basin margin, the latter a result of glacioeustatic forcing during an “everwet” climate. A major paleoenvironmental shift occurs in the late early Permian, which is reflected by the transition from fluvial to mixed fluvial-aeolian and ultimately aeolian dominant sedimentation by the late Permian. The transition from fluvial to aeolian dominant sedimentation is accompanied by a change in clay chemistry, sedimentary rock textual maturity, paleosol morphology and a three-fold increase in Paleozoic zircons in the mid to late Permian strata. Widespread loess deposits across equatorial Pangea during the Permian have been used to argue for the possibility of equatorial glaciers situated in highland settings during the early Permian. Conversely, our data suggest initiation of a substantial component of aeolian deposition across the field areas, which is coincident with widespread ice loss across high latitude Gondwana, and ultimately highlights the teleconnections between high latitude glaciation and the low latitude hydrologic cycle.
Over 10,000 published detrital zircon ages have been reprocessed (applying a +10% normal and reverse concordance range) and analysed to understand the evolution of the detrital zircon record of North‐West Africa during the Phanerozoic. Using dissimilarity and clustering analysis, shifts in detrital zircon populations allow interpretation of the evolution of source regions and source to sink systems throughout the Phanerozoic within the West Gondwana superfan. Previous thermochronology and field studies conducted across North‐West Africa indicate significant and sustained shifts in source regions in Meso‐Cenozoic times which are not recorded in the detrital zircon geochronology record. This discrepancy is most notable for Mesozoic to modern source to sink studies focused on the evolution of the Atlasic rift and opening of the Atlantic and Tethyan Oceans to the west and north respectively. Our results indicate a high degree of similarity between samples from Cambrian times onwards due to successive phases of sediment recycling. This highlights the need to integrate detrital zircon analysis with other techniques to provide confident reconstruction of sediment routing systems across Morocco. This systematic review also reveals the ubiquitous occurrence of Mesoproterozoic zircons within Moroccan sediment. No basement of this age is known from Northwest Africa – often described as the ’Mesoproterozoic Gap’, which was thought to be a diagnostic feature of sediment derived from the West African Craton. However, zircons of this age form 7% of all analysed zircons and are present in sediments from at least 700 Ma. The presence of this population is interpreted as strongly diagnostic of provenance from either the Amazonian Craton or the Eastern Gondwana Orogen within Central Africa. Their presence in the Moroccan detrital record from the Neoproterozoic onwards raises questions about the position of the West African Craton in the Proterozoic, and for the spatial extent of Mesoproterozoic orogeny within north Africa.
Detrital zircon age patterns are reported from quartz sandstones and metaquartzites in the Russet and Wangapeka formations (Western Province, Takaka Terrane) in Fiordland and northwest Nelson, and the Pegasus Group on Stewart Island. The latter indicate a possible maximum early Carboniferous depositional age with a significant Lower Devonian zircon component that suggests a source on the Campbell Plateau or Marie Byrd Land, West Antarctica. In contrast, Russet Formation ages indicate a correlation with Upper Ordovician, Wangapeka Formation quartz sandstones in northwest Nelson. These zircon age patterns have two major groups: late Mesoproterozoic (1200–1000 Ma) of Rodinia origin and Cambrian–late Neoproterozoic (700–500 Ma) of early Gondwana derivation. Both groups have local Zealandia provenances. In addition, there are unusually high proportions (to 20%) of early Paleoproterozoic and Archean zircons, 3500–2000 Ma, with significant age components, 2550–2450 Ma and ca 2800 and 2650 Ma, which are characteristic of an Expanded-Ur continent. Their high proportions of euhedral grains indicate a local source within a postulated Archean basement block at or near the eastern margin of the Takaka Terrane. A proposed Rodinia supercontinent reconstruction locates this Precambrian basement as a Zealandia component placed between Gawler and North Australia cratons of Australia and Yangtze Block of the South China Craton.
• KEY POINTS
• Pegasus Group, metaquartzites, Stewart Island are not correlated with the Russet Formation, Fiordland but are an Upper Devonian or lower Carboniferous sedimentary unit.
• Russet Formation high-grade metasandstones in Fiordland are correlated with the lower-grade and fossiliferous Upper Ordovician Wangapeka Formation in Nelson.
• Upper Ordovician sandstones in Western Province, New Zealand contain unusually high proportions of Neoarchean euhedral detrital zircons that suggest a local Zealandia source.
• An Archean block is proposed within the Rodinia supercontinent, between the Gawler and North Australia cratons of Australia and Yangtze Block of the South China Craton.
Detrital zircon U–Pb age patterns in sandstones from the Triassic–Cretaceous Clarence-Moreton Basin, eastern New South Wales and Queensland, unexpectedly reveal sediment sources overwhelmingly dominated (>70%) by Precambrian–Cambrian zircons, with virtually no input, as was anticipated, from the nearby Carboniferous, Permian or Triassic magmatic arcs and contemporary accretionary wedge associated with the New England Orogen. Some rare, youngest zircons (<5%) are mostly contemporaneous with the estimated depositional age. The older, reworked zircon populations can only be acquired by postulating either (1) an Australian provenance by long overland sediment pathways from the interior to the west, during one or more transport cycles, perhaps from within the Thomson Orogen, and then bypassing or crossing the New England Orogen without any local contribution from that sector or (2) a North Zealandia provenance with a shorter transport distance from a postulated basement block to the east, within the Northern Lord Howe Rise and Kenn Plateau. This would comprise late Mesoproterozoic (1200–1000 Ma) and late Neoproterozoic–Cambrian (700–500 Ma) igneous and metamorphic complexes, similar to that proposed in South Zealandia.
• KEY POINTS
• Triassic to Jurassic Clarence-Moreton Basin sedimentary rocks have provenances unlike their hinterland time-correlates in New South Wales and Queensland.
• The latter better share similarities with those in Murihiku Terrane, North Island, New Zealand.
• The provenance of Clarence-Moreton sediments is similar to that of time-correlates in New Caledonia, and it is postulated that they share a source region on the northern Lord Howe Rise or Kenn Plateau.
In this study, we present new experimental constraints on the thermal equations of state of corundum and Rh2O3(II)‐type Al2O3 up to 153 GPa and 3400 K using synchrotron X‐ray diffraction in laser‐heated diamond anvil cells. Corundum was observed to transform into a mixture of corundum and Rh2O3(II)‐type Al2O3 at 106 GPa and 2300 K, accompanied by a strong kinetic barrier. The Rh2O3(II)‐type Al2O3 further transforms into the CaIrO3‐phase at 156 GPa and 3700 K. The transition from corundum to Rh2O3(II)‐type Al2O3 along a normal mantle geotherm could lead to a 1.9(5)% increase in density (ρ) but a 0.6(3)% decrease in bulk sound velocity (VΦ). Al2O3 is one of the major components of the anorthositic crust once this old crust was subducted to the deep mantle. Using the obtained thermoelastic parameters, we further modeled ρ and VΦ profiles of primordial anorthositic crust and found that the subducted fate of the primordial anorthositic crust depended strongly on its temperature. Our modeling reveals that primordial anorthositic crust along a normal mantle geotherm could descend to the transition zone but be trapped at the topmost lower mantle with a greater VΦ. Sinking of the anorthositic crust to the lower mantle can only occur along a 500–1000 K colder slab geotherm.
On the passive margin of southern Brazil, where the availability of sediments and coastal system conditions were adequate for forming a Ti-Zr-bearing placer in the Holocene, could there be a source of detrital contribution other than the Precambrian South American cratons? To answer that, detrital zircon isotopes UPb and LuHf using the LA-ICP-MS method were performed. The UPb age pattern distribution of 866 zircon grains showed that 35.3% of the grains belong to the Neoproterozoic, which covers the Brasiliano orogenic belts. However, 9.1% of the total zircons analyzed (up to 12% in some samples) correspond to grains younger than 50 Ma, restricted to the Andean orogeny in southern South America. The Hf signature of the zircons stands out by pointing to five significant and distinct groups interpreted as coming from the Andean (0–50 Ma), Gondwanides (230–380 Ma), Famatinian (380–500 Ma), Brasiliano (850–541 Ma), and Grenville (900–1300 Ma) orogens, confirming an Andean fingerprint as source rocks in addition to the sediments originating from the craton. This Andean source is related to the distal sediment contribution from the La Plata River system and Argentina rivers that discharge in the Atlantic Coast. Based on a statistical and Hf isotopes approach, we defined that around 50% of the zircons grains were transported from the Argentina coast and La Plata River by the litoral drift for more than 1000 km to their final sink in the southern Brazilian coast.
The Mongol–Okhotsk Belt, the youngest segment of the Central Asian Orogenic Belt, formed by the evolution and closure of the Mongol–Okhotsk Ocean. The oceanic closure formed two volcanoplutonic belts: Selenge Belt in the north and Middle Gobi Belt in the south (in present day coordinates). However, the origin and tectonic evolution of the Mongol–Okhotsk Belt in general, the origin and formation age of the Middle Gobi Belt in particular, remain enigmatic. To better understand the history of the magmatic activity in the Middle Gobi Belt, we conducted geochemical, U–Pb geochronological, zircon Hf, whole-rock Nd isotopic analyses of volcanic and plutonic rocks of the Mandalgovi suite, the major component of the Middle Gobi Belt. Our results show that the Mandalgovi suite consists of (i) 265 ± 2 Ma biotite-granite; (ii) 250 ± 3 Ma hornblende-granitoids; (iii) their volcanic equivalents of both: and (iv) gabbro-diorites. The geochemical compositions indicate that their precursor magmas were derived from crustal source. The protoliths of the biotite and hornblende-granitoids were metagraywacke and metabasalt, respectively. They are characterized by positive whole-rock εNd(t) and zircon εHf(t) values, indicating the molten protoliths were juvenile crust. The biotite-granites formed by remelting of fore-arc sediments by ridge subduction and later hornblende-granites were emplaced at an intra-oceanic arc by the subduction of the Mongol–Okhotsk Ocean. We conclude that the magmatic rocks of the Middle Gobi formed in an active continental margin and/or intra-oceanic arc setting.
Declining radiogenic heat production since the Archaean has resulted in a secular evolution from a regime of numerous fast-moving small thin torsionally weak plates to the present regime of larger thicker torsionally stronger plates moving at an average rate of less than one-sixth of the Archaean rate; this has been accompanied by episodic changes in geological effects. By 2500 Ma B.P., about 85% of the present crustal mass had grown by the addition and amalgamation of mafic and calc-alkaline rocks in oceanic arcs at an average rate of 11.17 Pg/a. During the early Proterozoic, the first large cratons were stabilized and, locally, thickened and differentiated; the Proterozoic was an era of little continential growth, falling average sea level, and intracontinental deformation. By 700 Ma B.P. cratons had become much more stable, marginal accretionary terrains had begun to develop with an average Phanerozoic growth rate of 1.64 Pg/a, and blueschists and ophiolites sensu stricto witness the advent of the extant plate tectonic regime.
The cratonic blocks of South America have been accreted from 2.2 to 1.9 Ga, and all of these blocks have been previously involved in the assembly and breakup of the Paleoproterozoic Atlantica, the Mesoproterozoic to Neoproterozoic Rodinia, and the Neoproterozoic to Phanerozoic West Gondwana continents. Several mineralization phases have sequentially taken place during Atlantica evolution, involving Au, U, Cr, W, and Sn. During Rodinia assembly and breakup and Gondwana formation, the crust-dominated metallogenic processes have been overriding, responsible for several mineral deposits, including Au, Pd, Sn, Ni, Cu, Zn, Mn, Fe, Pb, U, P2O5, Ta, W, Li, Be and precious stones. During Rodinia breakup, epicontinental carbonate-siliciclastic basins were deposited, which host important non-ferrous base metal deposits of Cu–Co and Pb–Zn–Ag in Africa and South America. Isotope Pb–Pb analyses of sulfides from the non-ferrous deposits unambiguously indicate an upper crustal source for the metals. A genetic model for these deposits involves extensional faults driving the circulation of hydrothermal mineralizing fluids from the Archean/Paleoproterozoic basement to the Neoproterozoic sedimentary cover. These relations demonstrate the individuality of metal associations of every sediment-hosted Neoproterozoic base-metal deposit of West Gondwana has been highly influenced by the mineralogical and chemical composition of the underlying igneous and metaigneous rocks.
The principal paleogeographic characteristics of North and Central Africa during the Paleozoic were the permanency of large exposed lands over central Africa, surrounded by northerly and northwesterly dipping pediplanes episodically flooded by epicontinental seas related to the Paleotethys Ocean. The intra-continental Congo–Zaire Basin was also a long-lived feature, as well as the Somali Basin from Late Carboniferous times, in conjunction with the development of the Karoo basins of southern Africa. This configuration, in combination with eustatic sea-level fluctuations, had a strong influence on facies distributions. Significant transgressions occurred during the Early Cambrian, Tremadocian, Llandovery, Middle to Late Devonian, Early Carboniferous, and Moscovian.
This article introduces the name “Saharan Metacraton” to refer to the pre-Neoproterozoic––but sometimes highly remobilized during Neoproterozoic time––continental crust which occupies the north-central part of Africa and extends in the Saharan Desert in Egypt, Libya, Sudan, Chad and Niger and the Savannah belt in Sudan, Kenya, Uganda, Congo, Central African Republic and Cameroon. This poorly known tract of continental crust occupies ∼5,000,000 km2 and extends from the Arabian-Nubian Shield in the east to the Tuareg Shield to the west and from the Congo craton in the south to the Phanerozoic cover of the northern margin of the African continent in southern Egypt and Libya. The term “metacraton” refers to a craton that has been remobilized during an orogenic event but is still recognizable dominantly through its rheological, geochronological and isotopic characteristics. Neoproterozoic remobilization of the Saharan Metacraton was in the forms of deformation, metamorphism, emplacement of igneous bodies, and probably local episodes of crust formation related to rifting and oceanic basin development. Relics of unaffected or only weakly remobilized old lithosphere are present as exemplified by the Archean to Paleoproterozoic charnockites and anorthosites of the Uweinat massif at the Sudanese/Egyptian/Libyan boarder. The article explains why the name “Saharan Metacraton” should be used, defines the boundaries of the metacraton, reviews geochronological and isotopic data as evidence for the presence of pre-Neoproterozoic continental crust, and discusses what happened to the Saharan Metacraton during the Neoproterozoic. A model combining collisional processes, lithospheric delamination, regional extension, and post-collisional dismembering by horizontal shearing is proposed.
A simple two-reservoir. model with time-dependent transport coefficients between the reservoirs has been used to model the abundances of K, Ar, Rb, Sr, Sm, Nd, U, Th, and Pb and the isotopic compositions of Ar, Sr, Nd, and Pb in the earth's mantle and continental crust. The transport coefficients, like heat production, are considered to decay exponentially with time. Models which involve the whole mantle in generating the continental crust yield 87Sr/144 and 143Nd/144Nd ratios for the residual mantle which are higher and lower than midocean ridge basalts, respectively. A model which involves only half of the mantle in the production of continental crust produces a residual mantle with isotope ratios similar to those of midocean ridge basalt. The 40Ar/36Ar ratios in the atmosphere and suboceanic mantle are reproduced by this model without any inequality in the upward transport coefficients of K and Ar but with a smaller downward transport coefficient for Ar than for K. The results imply that the earth's crust may have developed by extraction of material from only half of the mantle and constrain the possible convective regimes that have existed in the mantle.
Recent seismological work has revealed new structures in the boundary
layer between the Earth's core and mantle that are altering and
expanding perspectives of the role this region plays in both core and
mantle dynamics. Clear challenges for future research in seismological,
experimental, theoretical and computational geophysics have emerged,
holding the key to understanding both this dynamic system and geological
phenomena observed at the Earth's surface.
The assembly of the Gondwana supercontinent during the waning stages of the Proterozoic provides a tectonic backdrop for the myriad biological, climatological, tectonic and geochemical changes leading up to, and including, the Cambrian radiation. A polyphase assembly of Gondwana during the East Africa, Brasiliano, Kuungan and Damaran orogenies resulted in an extensive mountain chain which delivered nutrients into a shifting oceanic realm. An analysis of key evolutionary events during this time period reveals the following (a) several fauna show well established endemism that may be rooted in a cryptic evolutionary pulse (c). 580 Ma (b) the margins of the Mirovian and Mawson Oceans formed the locus of radiation for the Ediacaran fauna (c) the margins of the Iapetan and Mirovian oceans form the olenellid trilobite realm (d) the margins of the Mawson and Paleo-Asian oceans are the birthplace of the so-called Gondwana Province fauna (e) evolutionary events associated with the Cambrian radiation were likely driven by internal (biological) changes, but radiation was enhanced and ecosystems became more complex because of the geochemical, ecological and tectonic changes occurring during Ediacaran–Cambrian periods.
We have reconstructed the paleogeography of continents, oceans and oceanic large igneous provinces (LIPs) since 1000 Ma in order to decode the history of the Pacific Superplume, using the most reliable recent data for accretional geology from orogens associated with ophiolites and greenstone belts, and of geochronologic and paleomagnetic data from each continent. From our reconstructions we have arrived at the following conclusions: (1) the Pacific Superplume was born at 750 Ma and broke-up the supercontinent Rodinia; (2) the African Superplume was born at 200 Ma and broke-up Pangea; (3) the Pacific Superplume was active episodically with culminations at 580-600 Ma, 280-230 Ma and 150-75 Ma; (4) during the formation of Rodinia much oceanic lithosphere from the Tethyan-Indian type ocean was subducted along paleo-trenches of proto-Grenville orogens along a V-shaped, double-sided convergent boundary around the continental lithosphere of Rodinia. These relations suggest that the massive volumes of lithosphere subducted under the Pacific-type orogens triggered the birth of the Pacific Superplume after 200 m.y. at the center of Rodinia.
Supercontinent amalgamation and dispersal has occurred repeatedly since the Archean. However, the mechanisms responsible for these events are unclear. Following supercontinent breakup, two geodynamically distinct oceans may be distinguished: an interior ocean formed between the dispersing continents, whose lithosphere is younger than the time of supercontinent breakup (TR); and an exterior ocean that surrounded the supercontinent prior to breakup, and consequently is dominated by lithosphere that is older than the time of breakup. In order to evaluate geodynamic models for supercontinent formation, it is essential to determine which of these two types of ocean is consumed during supercontinent amalgamation. Although much of the evidence needed is destroyed by subduction, vestiges of oceanic lithosphere are preserved in mafic complexes accreted to continental margins prior to terminal collision. Because the age contrast between interior and exterior oceans diminishes as the continents drift apart, the ages of the earliest accreted complexes are the most diagnostic of the ocean in which they formed. Constraints on the age of the mantle lithospheric sources (TDM) that give rise to these accreted complexes can be derived from Sm-Nd isotope systematics. In the case of Pangea, for example, the North American Cordillera represents an accretionary orogen along the leading edge of a dispersing supercontinent. Within this orogen, the oldest accreted oceanic terranes, characterized by high εNd values close to contemporary depleted mantle values, show similar crystallization and T model ages that imply crustal formation and arc activity during the lifespan of Pangea, that is, within the exterior Panthalassa ocean (i.e., TDM>TR). This example suggests that a similar approach applied to older orogens may constrain the relationship between continental margins and their accreted mafic complexes.Pangea was formed by closure of Paleozoic oceans (e.g., Iapetus and Rheic) that were formed after the ca. 550 Ma breakup of Pannotia. Uncontaminated mafic rocks from both oceans that have εNd values close to depleted mantle values at their respective times of emplacement show closely matching crystallization and depleted mantle model ages that do not exceed the age of rifting (i.e., TDM ≥ TR). This indicates that the oceanic lithospheric source of these suites was generated after the rifting of Pannotia, such that Pangea was formed by the closure of interior oceans (introversion). In contrast, mafic terranes accreted in orogens that terminated in the formation of the Late Neoproterozoic supercontinent Pannotia have Sm-Nd TDM model ages between ca. 1.2 and 0.71 Ga, implying that much of the oceanic lithosphere that was subducted and recycled to yield these complexes was formed before the ca. 755 Ma breakup of the supercontinent Rodinia (i.e. TDM > TR). These mafic complexes are therefore vestiges of oceanic lithosphere that formed within the peri-Rodinian ocean, such that Pannotia was formed by the closure of an exterior ocean (extroversion). This analysis suggests that Pangea and Pannotia were assembled by fundamentally distinct geodynamic processes. Hence, the "supercontinent cycle" may have a more complex origin than previously considered.
We carried out in situ U-Pb and Lu-Hf isotope analyses of detrital zircons from the Mississippi River in order to understand crustal reworking and continental growth rates. The U-Pb analyses for 416 zircons reveal three major peaks of crust formation at 2.8-2.6 Ga, 1.8-0.9 Ga, and after 0.2 Ga. Initial Hf isotope ratios were obtained for 402 of the dated zircons, and only 8{percnt} of the zircons have {epsivB} Hf(T)DM values less negative than -2.5. These data correspond to a crustal residence time of <120 m.y. This finding indicates that crustal reworking was a very important process in continental crust formation. The {epsivB} Hf(T)DM population demonstrates that reworking was predominant at 2.5-2.0 Ga and after 0.9 Ga, whereas juvenile crust formation dominated between 2.0 and 1.6 Ga. We calculated the mantle-extraction model ages to estimate the continental growth rate. Approximately half of the grains have model ages between 2.0 and 1.3 Ga, indicating rapid crustal growth during this time. The continental growth rate suggests that 15{percnt} and 78{percnt} crust in the source region of the zircons formed by 2.5 and 1.3 Ga, respectively.
Recent results of high-resolution seismic tomography and mineral physics experiments are used to study mantle dynamics of Western Pacific and East Asia. The most important processes in subduction zones are the shallow and deep slab dehydration and the convective circulation (corner flow) processes in the mantle wedge. The combination of the two processes may have caused the back-arc spreading in the Lau basin, affected the morphology of the subducting Philippine Sea slab and its seismicity under southwest Japan, and contributed to the formation of the continental rift system and intraplate volcanism in Northeast Asia, which are clearly visible in our tomographic images. Slow anomalies are also found in the mantle under the subducting Pacific slab, which may represent (a) small mantle plumes, (b) upwellings associated with the slab collapsing down to the lower mantle, or (c) sub-slab dehydration associated with deep earthquakes caused by the reactivation of large faults preserved in the slab. Combining tomographic images and earthquake hypocenters with phase diagrams in the systems of peridotite + water, we proposed a petrologic model for arc volcanism. Arc magmas are caused by the dehydration reactions of hydrated slab peridotite that supply water-rich fluids to the mantle wedge and cause partial melting of the convecting mantle wedge. A large amount of fluids can be released from hydrated MORB at depths shallower than 55 km, which move upwards to hydrate the wedge corner under the fore-arc, and never drag down to the deeper mantle along the slab surface. Slab dehydration reactions at 120 km depth are the antigorite-related 5 reactions which supply water-rich fluids for forming the volcanic front. Phase A and Mg-surssasite breakdown reactions at 200 and 300 km depths below 700 °C cause the second and third arcs, respectively. Moreover, the dehydration reactions of super-hydrous phase B, phases D and E at 500–660 km depths cause the fluid transportation to the mantle boundary layer (MBL) (410–660 km depth). The stagnant slabs extend from Japan to Beijing, China for over 1000 km long, indicating that the arc–trench system covers the entire region from the Japan trench to East Asia. We propose a big mantle wedge (BMW) model herein, where hydrous plumes originating from 410 km depth cause a series of intra-continental hot regions. Fluids derived from MBL accumulated by the double-sided subduction zones, rather than the India–Asia collision and the subsequent indentation into Asia, are the major cause for the active tectonics and mantle dynamics in this broad region.
This paper presents a brief synthesis of the current state of knowledge on the formation and break-up of the early-Neoproterozoic supercontinent Rodinia, and the subsequent assembly of Gondwanaland. Our discussions are based on both palaeomagnetic constraints and on geological correlations of basement provinces, orogenic histories, sedimentary provenance, the development of continental rifts and passive margins, and the record of mantle plume events.Rodinia assembled through worldwide orogenic events between 1300Ma and 900Ma, with all, or virtually all, continental blocks known to exist at that time likely being involved. In our preferred Rodinia model, the assembly process features the accretion or collision of continental blocks around the margin of Laurentia. Like the supercontinent Pangaea, Rodinia lasted about 150 million years after complete assembly. Mantle avalanches, caused by the sinking of stagnated slabs accumulated at the mantle transition zone surrounding the supercontinent, plus thermal insulation by the supercontinent, led to the formation of a mantle superswell (or superplume) beneath Rodinia 40–60 million years after the completion of its assembly. As a result, widespread continental rifting occurred between ca. 825Ma and 740Ma, with episodic plume events at ca. 825Ma, ca. 780Ma and ca. 750Ma.Like its assembly, the break-up of Rodinia occurred diachronously. The first major break-up event occurred along the western margin of Laurentia (present coordinates), possibly as early as 750Ma. Rifting between the Amazonia craton and the southeastern margin of Laurentia started at approximately the same time, but only led to break-up after ca. 600Ma. By this time most of the western Gondwanan continents had joined together, although the formation of Gondwanaland was not complete until ca. 530Ma.
A new model of whole mantle P-wave tomography is determined with a novel approach. A grid parameterization instead of blocks and spherical harmonics is adopted to express the Earth structure. Depth variations of the Moho, 410 and 660 km discontinuities are taken into account in the inversion. Ray paths and travel times are computed with an efficient 3-D ray tracing scheme. This new approach was applied to a large data set of ISC (International Seismological Center) travel times (P, PP, PcP, pP, Pdiff) to determine a whole mantle P-wave tomography. For the shallow mantle, the new model contains the general features observed in the previous models: a low-velocity ring around the Pacific Ocean basins and high-velocity anomalies under the old and stable continents in the depth range of 0–300 km. One significant difference from the previous models is that stronger and wider high-velocity anomalies are visible in the transition zone depths under the subduction regions, which suggests that most of the slab materials are stagnant in the transition zone before finally collapsing down to the lower mantle as a result of very large gravitational instability from phase transitions. Very slow anomalies exist in the upper mantle right beneath the Wudalianchi and Changbai active volcanoes in Eastern China, right above the stagnant Pacific slab in the transition zone, suggesting that the origin of the intraplate volcanism in East Asia is closely related to the Pacific plate subduction process, such as deep slab dehydration and convective circulation in the mantle wedge. Plume-like slow anomalies are clearly visible under the major hotspot regions in most parts of the mantle, in particular, under Hawaii, Iceland, South Pacific and Africa. The slow anomalies under South Pacific and Africa have lateral extensions of over one thousand kilometers and exist in the entire mantle, representing two superplumes. The Pacific superplume has a larger spatial extent and stronger slow anomalies than that of the Africa superplume. The Hawaiian plume is not part of the Pacific superplume. The slow anomalies under hotspots usually do not show a straight pillar shape, but exhibit winding images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. As a consequence, hotspots are not really fixed but can wander on the Earth’s surface, as evidenced by the recent paleomagnetic and numeric modeling studies. Wider and more prominent slow anomalies are visible at the core–mantle boundary (CMB) than most of the lower mantle, and there is a good correlation between the distribution of slow anomalies at the CMB and that of hotspots on the surface, suggesting that most of the strong mantle plumes under the hotspots originate from the CMB. However, there are some small-scaled, weak plumes originating from the transition zone or mid mantle depths.
In this work we will examine the available evidence for the position of the cratonic masses that formed West Gondwana, in the Neoproterozoic, such as Amazonia, West Africa, São Francisco-Congo, Rio de La Plata and Kalahari. Some emphasis will be given to South America, and the smaller continental masses or microcontinents, that are usually forgotten in the exercise of global reconstruction, will also be considered. Among others, such tectonic units are the Central Goiás massif, the Borborema/Trans-Saharan block, as well as the Luiz Alves, Paraná and Pampia cratonic fragments.Taking into account the relevant paleomagnetic and geochronological data, it is necessary to consider a large time interval for the process of break up of Rodinia. Signals of extension and fracturing are as old as 1000-1100 Ma, when mafic dyke swarms are observed on the São Francisco-Congo craton, and final break out is reported as young as 750 Ma. On the other hand, the formation of intra-oceanic magmatic arcs within the large Goiás Ocean occurred prior to 930 Ma ago. Moreover, for the make up of Gondwana, the first continental collisions are reported at ca. 800 Ma, and the most important accretion episodes are the ones between 650 and 500 Ma, corresponding to the Brasiliano/Pan-African Orogenic Cycle. Therefore, it is apparent that fragmentation of Rodinia is partially synchronous with agglutination of Gondwana.
In this classic series-generating paleontology/geology book published by Columbia University Press, Mark and Dianna McMenamin explore the evolutionary and paleoecological questions associated with the Cambrian Explosion. This book both names and maps the initial paleogeographic reconstruction of the billion year old supercontinent Rodinia. The observations and interpretations in this book, particularly as regards the timing of the Cambrian Explosion, have stood the test of time. The issues identified herein as most important for understanding the Proterozoic-Cambrian transition, remain so today.
Evidence supports the hypothesis that the Laurentian and East Antarctic-Australian cratons were continuous in the late Precambrian and that their Pacific margins formed as a conjugate rift pair. A geometrically acceptable computer-generated reconstruction for the latest Precambrian juxtaposes and aligns the Grenville front that is truncated at the Pacific margin of Laurentia and a closely comparable tectonic boundary in East Antarctica that is truncated along the Weddell Sea margin. Geologic and paleomagnetic evidence also suggests that the Atlantic margin of Laurentia rifted from the proto-Andean margin of South America in earliest Cambrian time. -from Author
Laurentia, the Precambrian core of the North American Continent, is surrounded by late Precambrian rift systems. Within the supercontinent of Pangea, North America therefore constitutes a "suspect terrane' because its origin as a discrete continent and geographic location prior to the late Paleozoic are uncertain. A geometric and geologic fit can be achieved between the Atlantic margin of Laurentia and the Pacific margin of the Gondwana craton. In the reconstruction, the ca. 1.0 Ga Grenville belt continues beneath the ensialic Andes of the present day to join up with the 1.3-1.0 Ga San Ignacio and Sonsas-Aguapei orogens of the Transamazonian craton. The fit supports and refines suggestions that Laurentia broke out from between East Antarctica-Australia and embryonic South America during the Neoproterozoic, prior to the opening of the Pacific Ocean basin and amalgamation of the Gondwana supercontinent. This implies that there may have been two supercontinents during the Neoproterozoic, before and after opening of the Pacific Ocean. -from Author
Plate tectonics supplies cold slabs to the mantle transition zone at 670km depth where they are stagnant ca.100-400 m.y. until the catastrophic gravitational collapse due to the endothermic nature of the phase transition. Cold plume thus formed flows down onto the outer core to refrigerate the metallic Fe-Ni liquid to initiate new downflow in the core. Super-upwelling of mantle flow appears as a passive response of cold plume which is of primary importance of the Earth's dynamics in a cold planetary environment of space. Supercontinents break up by a chain of super-upwelling of hot mantle, and the resultant fragmented tectospheres capped by pre-1.9 Ga continents are drifted, dispersed and scattered in the shrinked superocean with time. Cold plumes develop in the lower mantle at random at an earlier stage of continental dispersion. Once it is formed in the lower mantle, mantle convection patterns in the upper mantle tends to be strongly controlled by a sole superplume of downwelling in the lower mantle. Plate tectonics is a superficial phenomenon on the Earth less than 1/10 of Earth's radius, whereas columnar plume flows dominate in major parts of deeper mantle. -from Author
Ultra-low velocity layering at the Earth's core-mantle boundary (CMB) has now been detected using a variety of seismic probes. P-and S-wave velocity reductions of up to 10's of percent have been mapped in a thin (5–50 km) layer, which commonly underlies reduced seismic shear wave speeds in the overlying few 100 km of the mantle. Ultra-low velocity zones (ULVZ) contain properties consistent with partial melt of rock at the very base of the mantle. Strong evidence now exists for a significant density increase in the layer (∼5–10% greater than reference models), which must be included in dynamical scenarios relating ULVZ partial melt to deep mantle plume genesis. 3-D geodynamical calculations involving an initially uniform dense layer in the lowermost few 100 km of the mantle result in thermo-chemical piles that are geographically well-correlated with seismic tomography low velocities, when past plate motions are imposed as a surface boundary condition. The hottest lower mantle regions underlay edges of the dense thermo-chemical piles. A scenario is put forth where these piles geographically correlate with ultra-low velocity zones, and subsequent mantle plume genesis.
Field, geochemical and structural evidence collectively indicate that the Upper Pro-terozoic to Lower Palaeozoic (Pan-African) continental crust of the Arabian—Nubian Shield evolved through a period of about 700 Ma (1200–500 Ma) by progressive craton-ization (continentalization) of numerous intra-oceanic island arcs. An episodic continuum of magmatic, metamorphic and sedimentary processes, similar to those operating above present-day oceanic and then continental subduction zones, is envisaged. Structural deformation and ophiolite obduction occurred primarily during phases of arc collision at c. 1000, 800 and 600 Ma. Although evidence presented relates to the Arabian—Nubian Shield, the cratonized island-arc model seems to be applicable in Africa as far south as Ethiopia in the east and across northern Africa as far as the West African Archaean craton. If this is the case then c. 5 × 108 km3 of new continental crust was produced in the Upper Proterozoic by plate-tectonic processes directly analagous to those of present-day destructive plate margins.
In the history of modeling plate motion, stage poles (or Euler poles)
and rotation angles are often used to describe the rotation of the plate
relative to hotspots. As the model improves, more and more stages are
required to fit observed data of locations and ages of seamounts that
are created by the hotspots. To describe the plate motion with the stage
poles however, one must assume that Euler poles are fixed to the hotspot
reference frame for certain intervals of time. Generally speaking, Euler
poles do not need to be fixed relative to hotspots, and without knowing
the timing and the numbers of the stages, the accurate positions of the
stage poles are never determined. Therefore, we presented a new method
for calculating total rotation poles for a plate motion with respect to
hotspots irrespective of whether the stage poles are fixed relative to
hotspots or not. A new model for the motion of the Pacific plate
obtained by this method provides a better fit to the positions and the
ages of the observed hotspot tracks of the Pacific plate than the
previous models do. Most of the previous models do not have errors
assigned, but this suggests that the actual size of the errors are much
larger than previously estimated, and that Euler pole may move more
rapidly than formerly considered. The new method is also useful for
investigating the validity of the assumptions of fixed hotspots and a
rigid plate. From the fact that the new model can explain positions and
ages of observed hotspot tracks that are not used to construct the
model, the upper limits of mean motion as a result of the combination of
the inter-hotspot motion and the intra-plate deformation in the Pacific
plate is estimated to be about 2 to 3 mm/yr.
The Chewore Inliers are a group of isolated metamorphosed basement inliers located in the Zambezi Rift Valley of northern Zimbabwe close to the triple junction between the Irumide, Zambezi and Mozambique belts of south central Africa. Four contrasting litho-tectonic terranes have been recognised in these basement inliers, namely the Granulite, Quartzite, Zambezi and Ophiolite Terranes, with a protracted geological history ranging from the Mesoproterozoic to Neoproterozoic. The southernmost terrane comprises a suite of bodies that define an ophiolite (the Chewore Ophiolite, previously dated at 1393±22 Ma) and an island arc (the Kaourera Arc). We provide a detailed account of the lithological variation and structural evolution of the Kaourera Arc. We also present new UPb zircon ages of 1082±7 Ma and 517±5 Ma from a meta-dacite, which we interpret to record arc magmatism and subsequent metamorphism. The crystallisation age of the Kaourera Arc is thus ∼300 million years younger than the adjacent Chewore ophiolite, but is similar to UPb 1080 Ma ages from orthogneisses in the Granulite, Quartzite and Zambezi terranes. The geochemistry of these orthogneisses indicate that they may have formed in a continental margin arc, active in a similar time frame to the Kaourera Arc. Neoproterozoic tectonometamorphism, dated here at ∼517 Ma, was dominated by crustal-thickening and northeast (present-day coordinates) tectonic transport. This tectonothermal episode most likely resulted from the final collision between the Congo and Kalahari cratons, with the cryptic suture and orogenic root zone located between the Chewore Inliers and the Zimbabwe Craton, underneath the Karoo deposits of the Zambezi rift basin.
From the extraterrestrial telescopic, space probe, meteorite and returned sample studies of planetary evolution, and terrestrial evidence for early differentiation of core and fluid spheres and continental crust, the conclusion is inescapable that large terrestrial planets of our solar system underwent essentially immediate differentiation into relatively constant-volume core, depleted mantle, enriched crust and fluid reservoirs. The idea that the Earth's crust has grown is a myth dating from the 19th century and was established as geochemical dogma in the 1950s and 1960s. It has survived by inertia and repetition and endless self-citation. -from Author
Relative motions poles describing the displacement histories between the Pacific plate and once adjacent oceanic plates (Farallon, Kula, Izanagi I, Izanagi II, and Phoenix) were derived for the late Mesozoic and Cenozoic eras. Because fracture zone and magnetic anomaly data are generally available from the Pacific plate but not from adjacent plates, a new method of analysis for onesided data was required. This analysis produced stage poles and rates of relative plate motion and estimates of their confidence regions. Magnetic anomaly numbers and their assigned ages are both given in the text and in tables of finite rotation stage poles. Errors in the timing of stage boundaries are estimated to be 3-5 m. y. , reflecting uncertainty in the ages of the magnetic lineations and possible errors in identifying anomalies.
Spinel-bearing high Mg-Al granulites of the Vizianagram area in the Eastern Ghats granulite belt show textural features clearly establishing that the association spinelss + quartz + Fe-Ti oxide solid solution ± sillimanite ± porphyroblastic orthopyroxene was stable during peak metamorphic conditions. Pressure-temperature (P-T) conditions estimated from both mineralogical thermobarometry and phase-equilibrium limitations indicate that the peak metamorphism occurred under ultrahigh-T conditions (>1000 °C) at 8 9 kbar pressure. Retrograde P-T conditions of 750 800 °C, 6 7 kbar are deduced from the compositions of coronal garnet and orthopyroxene, which have rims of spinel against quartz, indicating significant cooling with slight lowering of pressure. Quartz associated with the ultrahigh-T assemblage at Vizianagram contains ubiquitous single-phase carbonic inclusions as isolated clusters that belong to two categories. Group I shows extremely high density (homogenization temperature: -51 ± 1.8 °C; density 1.15 g/cm3) and group II trapped relatively lower density fluids (homogenization temperature: -18.4 ± 2.4 °C; density 1.05 g/cm3). The iso chores for group I inclusions pass through the peak metamorphic P-T conditions, whereas those for group II coincide with the P-T conditions of the formation of coronal garnet and orthopyroxene. Our study is the first report of very high density CO2 associated with the Eastern Ghats granulite belt rocks and provides a strong case for the presence of CO2-rich fluids during ultrahigh-T metamorphism at lower crustal levels.
The mantle plume hypothesis is now widely known to explain hotspot volcanoes, but direct evidence for actual plumes is weak, and seismic images are available for only a few hotspots. In this work, we present whole-mantle tomographic images under 60 major hotspots on Earth. The lateral resolution of the tomographic images is about 300 km under the continental hotspots and 400–600 under the oceanic hotspots. Twelve plume-like, continuous low-velocity (low-V) anomalies in both the upper and lower mantle are visible under Hawaii, Tahiti, Louisville, Iceland, Cape Verde, Reunion, Kerguelen, Amsterdam, Afar, Eifel, Hainan, and Cobb hotspots, suggesting that they may be 12 whole-mantle plumes originating from the core–mantle boundary (CMB). Clear upper-mantle low-V anomalies are visible under Easter, Azores, Vema, East Australia, and Erebus hotspots, which may be 5 upper-mantle plumes. A mid-mantle plume may exist under the San Felix hotspot. The active intra-plate volcanoes in Northeast Asia (e.g., Changbai, Wudalianchi, etc.) are related to the stagnant Pacific slab in the mantle transition zone. The Tengchong volcano in Southwest China is related to the subduction of the Burma microplate under the Eurasian plate. Although low-V anomalies are generally visible in some depth range in the mantle under other hotspots, their plume features are not clear, and their origins are still unknown. The 12 whole-mantle plumes show tilted images, suggesting that plumes are not fixed in the mantle but can be deflected by the mantle flow. In most cases, the seismic images under the hotspots are complex, particularly around the mantle transition zone. A thin low-V layer is visible right beneath the 660-km discontinuity under some hotspots, while under a few other hotspots, low-V anomalies spread laterally just above the 660-km discontinuity. These may reflect ponding of plume materials in the top part of the lower mantle or the bottom of the upper mantle. The variety of behaviors of the low-V anomalies under hotspots reflects strong lateral variations in temperature and viscosity of the mantle, which control the generation and ascending of mantle plumes as well as the flow pattern of mantle convection.
To this day, there is a great amount of controversy about where, when and how the so-called supercontinents--Pangea, Godwana, Rodinia, and Columbia--were made and broken. Continents and Supercontinents frames that controversy by giving all the necessary background on how continental crust is formed, modified, and destroyed, and what forces move plates. It also discusses how these processes affect the composition of seawater, climate, and the evolution of life. Rogers and Santosh begin with a survey of plate tectonics, and go on to describe the composition, production, and destruction of continental and oceanic crust, and show that cratons or assemblies of cratons became the first true continents, approximately one billion years after the earliest continental crust evolved. The middle part of the book concentrates on supercontinents, beginning with a discussion of types of orogenic belts, distinguishing those that formed by closure of an ocean basin within the belt and those that formed by intracontinental deformation caused by stresses generated elsewhere. This information permits discrimination between models of supercontinent formation by accretion of numerous small terranes and by reorganization of large old continental blocks. This background leads to a description of the assembly and fragmentation of supercontinents throughout earth history. The record is most difficult to interpret for the oldest supercontinent, Columbia, and also controversial for Rodinia, the next youngest supercontinent. The configurations and pattern of breakup of Gondwana and Pangea are well known, but some aspects of their assembly are unclear. The book also briefly describes the histories of continents after the breakup of Pangea, and discusses how changes in the composition of seawater, climate, and life may have been affected by the sizes and locations of continents and supercontinents.
The anhydrous mineral assemblages that characterize granulite facies rocks, including charnockites and ultrahigh-temperature rocks, require that water activity was buffered to low levels during their formation. One of the popular models invokes the influx of CO2-rich fluids to generate dry mineral assemblages. Here we synthesize field, petrologic, fluid inclusion and stable isotopic evidence from a variety of lithologies which suggests that CO2 flushing could have played an active role in granulite petrogenesis. Available mineralogical and stable isotopic data indicate that the carbonic fluids were derived either from proximal sources through decarbonation reactions of interlayered carbonate lithologies or from deep-seated reservoirs in the sub-lithospheric mantle. We present results from thermodynamic computations in appropriate petrogenetic systems to quantitatively evaluate CO2 generation from calc-silicate rocks as well as model mantle peridotite. Our calculations demonstrate that CO2 release occurs in both cases under the P–T conditions and tectonic settings inferred for the formation of charnockites and ultrahigh-temperature granulites.
Phanerozoic addition rates to the continental crust are calculated by
using seismic profiles through magmatic arcs to measure the crustal
volumes added during the active lifespans of the arcs. Data for 17 arcs
give addition rates per kilometer of arc in the range 20 to 40 km³
km-1 Ma-1. From these data we deduce a world-wide
addition rate of 1.65 km³ a-1 after adding other
contributions to the formation of the continental crust, e.g., from hot
spot volcanism. We infer a subtraction rate, mainly by subducting
sediments, of 0.6 km³ a-1 and arrive at a net crustal
growth rate of about 1 km³ a-1. Growth of the
continental crust is necessary to maintain approximately constant
freeboard, because the secular decline in the heat production of the
mantle causes the ocean basins to deepen. An equation for the growth of
the continents as a function of the decline in terrestrial heat flow
yields approximately constant growth rate since the Archean of 0.9
km³ a-1, in good agreement with the above estimate. On
the average, Archean growth rates must have been 3 to 4 times the
present rate. Island arc growth rates are inadequate to explain the
formation of the Arabian-Nubian Shield and the Archean
granite-greenstone terrain of the Superior Province, and a captured
island chain in Oregon. We confirm the oceanic island origin of the
Oregon terrain on the basis of the large growth rates of hotspot
islands.
Episodic growth of continental crust and supercontinents at 2.7, 1.9, and 1.2 Ga may be caused by superevents in the mantle as descending slabs pile up at the 660-km seismic discontinuity and then catastrophically sink into the lower mantle. Superevents, in turn, may comprise three or four events, each of 50–80 My duration, and each of which may reflect slab avalanches at different locations and times along the 660-km discontinuity. Superplume events in the late Paleozoic and Mid-Cretaceous may have been caused by minor slab avalanches as the 660-km discontinuity became more permeable to the passage of slabs with time. The total duration of a superevent cycle decreases with time reflecting the cooling of the mantle.
Three Grenville-age provinces can be distinguished in East Antarctica with U-Pb zircon data. The Maud, Rayner, and Wilkes provinces each have a distinctive age signature for late Mesoproterozoic early Neoproterozoic magmatism and high-grade metamorphism and are correlated with similar rocks in the Namaqua-Natal (Africa), Eastern Ghats (India), and Albany-Fraser (Australia) provinces, respectively. These crustal segments represent three separate collisional orogens. They are separated by regions of intense late Neoproterozoic Early Cambrian tectonism, consistent with their juxtaposition during the final assembly of Gondwana and indicating that previous models for a single, continuous, Grenville-age mobile belt around the East Antarctic coastline should be discarded.
Granitic rocks in the west-central Adirondack Highlands of New York State include both relatively homogeneous charnockitic and hornblende granitic gneisses (CG), that occur in thick stratiform bodies and elliptical domes, and heterogeneous leucogneisses (LG), that commonly are interlayered with metasedimentary rocks. Major- and trace-element geochemical analyses were obtained for 115 samples, including both types of granitoids. Data for CG fail to show the presence of more than one distinct group based on composition. Most of the variance within the CG sample population is consistent with magmatic differentiation combined with incomplete separation of early crystals of alkali feldspar, plagioclase, and pyroxenes or amphibole from the residual liquid. Ti, Fe, Mg, Ca, P, Sr, Ba, and Zr decrease with increasing silica, while Rb and K increase. Within CG, the distinction between charnockitic (orthopyroxene-bearing) and granitic gneisses is correlated with bulk chemistry. The charnockites are consistently more mafic than the hornblende granitic gneisses, although forming a continuum with them. The leucogneisses, while generally more felsic than the charnockites and granitic gneisses, are otherwise geochemically similar to them. The data are consistent with the LG suite being an evolved extrusive equivalent of the intrusive CG suite.
Thrusts interspersed with lateral ramp and wrench structures mark the join between Proterozoic Eastern Ghats Mobile Belt and Archaean cratons of the eastern India. The join, referred to as Terrane Boundary Shear Zone, exhibits an arcuate geometry at the NW margin of the Eastern Ghats where the mobile belt shows the presence of northwesterly verging nappes. Based on this, the area has been described to represent the salient part of a fold thrust belt. Juxtaposition of the granulites over the low grade craton is largely attributed to thrusting along the terrane boundary shear zone. As the folds are disoriented and the granulites are retrograded along the thrusts, the terrane boundary shear zone is interpreted to be a retrograde shear zone. The shear zone hosts a number of synkinematic alkali intrusive rocks that constrain the age of thrusting to 1.4 Ga. In the correlative framework of Gondwanaland the terrane boundary shear zone is very likely to be contiguous with the Rayner-Napier boundary of Antarctica.
The proto-Darling Fault zone and its successor, the Darling Fault, extend for 1, 000 km along the western continental margin of Australia and appear to have been active at several periods during the geological past. Deformation commenced at ∼2,570 Ma and affected Late Archaean granitoids along the western margin of the Yilgarn Craton. Much of the later activity reflects events related to the accretion and breakup associated with the Rodinia and Gondwanaland supercontinent cycles.In the north, rocks of the Northampton and Mullingarra Complexes form part of a high-grade Grenvillian orogenic belt lying to the west of the Darling Fault, referred to as the Pinjarra Orogen. They underwent granulite facies metamorphism ∼1080 Ma ago and form part of the global collisional event that resulted in the amalgamation of Rodinia. These rocks extend southward beneath Phanerozoic sedimentary cover (the Perth Basin), where they are constrained to the east by the Darling Fault and to the west by the Dunsborough Fault, the latter marking the eastern boundary of the Leeuwin Complex.The Leeuwin Complex is a fragment of Pan-African crust that has traditionally been considered part of the Pinjarra Orogen. It is composed predominantly of upper amphibolite to granulite facies felsic orthogneisses derived from A-type, anorogenic granitoids. Conventional and SHRIMP U-Pb zircon geochronology has established that the granitoids evolved between ∼780 Ma and ∼520 Ma and were metamorphosed at ∼615 Ma. These events are equated with rifting associated with the breakup of Rodinia. Sm-Nd whole rock data support the juvenile nature of the crust and provide no evidence for the involvement of pre-existing Archaean continental material.During the Phanerozoic, the Dunsborough and Darling Faults were reactivated, as normal faults defining the inner arm of a major rift system within Eastern Gondwanaland and controlling sedimentation in the Perth Basin that now overlies the Grenvillian terrane. Major normal movement on the Darling Fault ceased by the Late Jurassic and it appears that continental breakup in the Early Cretaceous occurred along fractures closely related to the western boundary of the Leeuwin Complex that defined the eastern margin of the outer arm of the rift system. Breakup between Australia and Greater India commenced at ∼132 Ma and was followed by eruption of the Bunbury Basalt at 130 Ma and 123 Ma. This possibly resulted from hot spot activity beneath Eastern Gondwanaland and may have been a reflection of the Kerguelen plume, though the evidence is equivocal.It is argued from the petrographic, geochemical and isotopic characteristics, together with the likely contiguity of the Eastern Gondwanaland continents since the assembly of Rodinia, that the Leeuwin Complex evolved within an intracrustal rift and is not an exotic terrane. It is distinct from adjacent portions of the Pinjarra Orogen and should be considered a separate terrane. It is recommended that use of the term ‘Pinjarra Orogen’ be confined to rocks recording the Grenvillian events, thereby excluding those rocks (the Leeuwin Complex) that evolved during the later Pan-African orogeny.
The formation of Gondwana during the late Neoproterozoic to early Cambrian times (550-530 Ma) was traditionally viewed as the welding of two, more or less contiguous, Proterozoic continental masses called East and West Gondwana. The notion of a united West Gondwana is no longer tenable as a wealth of geochronologic and structural data indicate major orogenesis amongst its constituent cratons during the final stages of greater Gondwana assembly. The idea that East Gondwana may also have formed through the amalgamation of a collage of cratonic nuclei during the Cambrian is controversial. Recent paleomagnetic, geochronologic and structural data from elements of East Gondwana indicate that its formation may have extended well into Cambrian time. Thus, the terms ‘East’ and ‘West’ Gondwana may be relegated to convenient geographical terms rather than any connotation of tectonic coherence during the Proterozoic. In addition, the paleomagnetic data also challenge the conventional views of the Neoproterozoic supercontinent Rodinia and the SWEAT fit. Alternative variants including Protopangea and AUSWUS are not supported by paleomagnetic data during the interval 800–700 Ma.
In a comprehensive U–Pb electron microprobe study of zircon and monazite from the khondalite belt of Trivandrum Block in southern Kerala, we present age data on five key metapelite locations (Nedumpara, Oottukuzhi, Kulappara, Poolanthara and Paranthal). The rocks here, characterized by the assemblage of garnet–sillimanite–spinel–cordierite–biotite–K–feldsapr–plagiocalse–quartz–graphite, have been subjected to granulite facies metamorphism under extreme thermal conditions as indicated by the stability of spinel + quartz and the presence of mesoperthites that equilibrated at ultrahigh-temperature (ca. 1000 °C) conditions. The oldest spot age of 3534 Ma comes from the core of a detrital zircon at Nedumpara and is by far the oldest age reported from this supracrustal belt. Regression of age data from several spot analyses in single zircons shows “isochrons” ranging from 3193 ± 72 to 2148 ± 94 Ma, indicating heterogeneous population of zircons derived from multiple provenance. However, majority of zircons from the various localities shows Neoproterozoic apparent ages with sharply defined peaks in individual localities, ranging between 644–746 Ma. The youngest zircon age of 483 Ma was obtained from the outermost rim of a grain that incorporates a relict core displaying ages in the range of 2061–2543 Ma.
If a Paleoproterozoic supercontinent broke up between 1.6 and 1.5 Ga, the distribution of sutures shows that the breakup was not complete. At least two large cratons, Atlantica (Amazonia, Congo, West Africa and probably North Africa and Rio de la Plata) and Arctica (Laurentia, Siberia, Baltica, North Australia and North China), survived the breakup and later become part of Rodinia.
The Neoproterozoic global reorganisation that saw the demise of Rodinia and the amalgamation of Gondwana took place during an incredibly dynamic period of Earth evolution. To better understand the palaeogeography of these times, and hence help quantify the interrelations between tectonics and other Earth systems, we here integrate Neoproterozoic palaeomagnetic solutions from the various blocks that made up eastern Gondwana, with the large amount of recent geological data available from the orogenic belts that formed as eastern Gondwana amalgamated. From this study, we have: (1) identified large regions of pre-Neoproterozoic crust within late Neoproterozoic/Cambrian orogenic belts that significantly modify the geometry and number of continental blocks present in the Neoproterozoic world; (2) suggested that one of these blocks, Azania, which consists of Archaean and Palaeoproterozoic crust within the East African Orogen of Madagascar, Somalia, Ethiopia and Arabia, collided with the Congo/Tanzania/Bangweulu Block at ∼ 650–630 Ma to form the East African Orogeny; (3) postulated that India did not amalgamate with any of the Gondwana blocks until the latest Neoproterozoic/Cambrian forming the Kuunga Orogeny between it and Australia/Mawson and coeval orogenesis between India and the previously amalgamated Congo/Tanzania/Bangweulu–Azania Block (we suggest the name ‘Malagasy Orogeny’ for this event); and, (4) produced a palaeomagnetically and geologically permissive model for Neoproterozoic palaeogeography between 750 and 530 Ma, from the detritus of Rodinia to an amalgamated Gondwana.
The geochronological evolution of early Archaean Amı̂tsoq gneisses from southern West Greenland is reassessed here using the well-established cathodoluminescence imaging method both to reveal previously undocumented complex zircon growth histories and to control positioning of ion-microprobe U–Th–Pb analyses. Several of the gneisses typically contain zircon grains with ≥3.8 Ga cores of igneous origin, mostly completely mantled by growth banded magmatic zircon at ca. 3.65 Ga and in turn partly mantled by late Archaean metamorphic overgrowths at ca. 2.7 Ga. The ≥3.8 Ga cores are regarded as inherited, with apparent dates ranging down to ca. 3.65 Ga reflecting differential Pb loss. This contrasts with published views interpreting ≥3.8 Ga dates as emplacement ages of the host rock to the zircons, with all younger ages representing later Pb loss and/or metamorphic recrystallisation. Two of the analysed gneisses have discordant relationships to metasedimentary enclaves containing accessory apatite with graphite inclusions whose C-isotope ratios have been considered as biogenic in origin. The present data show that the minimum age of the enclaves is 3.65 Ga and not 3.85 Ga as previously claimed. This has important implications for the current debate on the possibility of temporal overlap of earliest life with a bolide impact scenario terminating at ≥3.8 Ga (as on the moon). We also discuss the implication of the discovery of highly complex internal structures in Amı̂tsoq gneiss zircons for the interpretation of published, zircon-derived Lu–Hf information.
In order to better understand continental growth history, we have determined the U–Pb age of about 1500 detrital zircons from river sands in three major rivers in North America and South America, and have estimated the rate of continental growth in order to discuss the linkage between continental growth and the thermal evolution of the mantle. The method for estimating continental growth from the age population of a significant number of detrital zircons in river sands has three advantages; (1) the almost even collection of zircons from sedimentary rocks and granitic basements in the hinterlands of the major rivers, (2) determination of the age of juvenile crust due to the high closure temperature of the U–Pb systematics of zircons, and the removal of the influence of recycling of crustal materials within the continental crust, and (3) direct determination of the age of continental formation.
The Neoproterozoic–Cambrian Kaoko Belt is an orogen-scale (800 × 180 km) transpressional system important in the amalgamation of West Gondwana. Mid-crustal transpression at amphibolite to granulite facies conditions is dominated by two major, > 400 km exposed, strike-slip shear zones bounding a 20–40 km wide high-grade Orogen Core. To the east, a deeply buried nappe-dominated Escape Zone has inverted metamorphic sequence and verges outwards onto a platformal foreland. To the west, an arc-like Neoproterozoic Coastal Terrane was amalgamated and variably reworked during transpression. The major Purros and Three Palms Mylonite Zones have calculated shear displacements on the order of 120–180 km. These shear zones are moderately to steeply dipping mylonite zones of 1–5 km width, are arcuate and curvilinear in map view and show along-strike variation in slip kinematics. Also highly curved in vertical section, the shear zones define a flower to half-flower geometry for the Orogen Core. An oblique network of mylonitic shear zones, akin to Riedel shears, links the major shear zones and defines regional-scale shear lozenges internally deformed by tight upright folding and shear fabrics. These shear zones create domains in the Orogen Core with varying dominance of pure shear (in shear lozenges) and simple shear (in shear zones). However, absence of dip-slip domains and the smoothly continuous traces of sub-horizontal to shallow and acute, oblique stretching lineations across all parts of the belt, preclude marked kinematic partitioning and the internal part of the belt resembles large-scale triclinic shear. Clast aspect ratios, boudin train extension, sheath fold aspect geometry, degree of rotation of planes producing flanking folds, composite S–C foliations, pressure fringes on pyrite and garnet porphyroclasts provide a semi-quantitative measure of strain intensity. Average strain ratios are X/Z > 40:1 for the major shear zones, X/Z > 12:1 for the Orogen Core, X/Z > 8:1 for the Escape Zone and X/Z > 3:1 for the Coastal Terrane. A more continuous pattern of strain intensity across the whole belt is mapped using a qualitative foliation intensity index. Foliation traces have a sigmoidal pattern in the Orogen Core, swinging from sub-parallel to the boundary shear zones to higher acute angles in the internal parts. Deformation character also varies from upright open folding in amphibolite facies domains in the north, upright tight chevron folding in a low-grade central domain, to a high-grade domain of tight to isoclinal inter-folded basement and cover, with inclination decreasing towards the south.The Kaoko Belt is a well-exposed sector of an extensive (3000 km long), broad (400 km) arcuate orogenic system “Adamastor Orogen” that amalgamated West Gondwana, bringing the South American (Sao Francisco and Rio de la Plata Cratons) and African (Kalahari and Congo Cratons) components together. Though a complex system, most sectors involved oblique collision and accretion of magmatic arcs of 660–610 Ma age, followed by peak metamorphism and main phase transpressional orogenesis between 585 and 560 Ma, with shear zones remaining active until ∼ 530 Ma. This E–W amalgamation immediately pre-dates the final N–S amalgamation of Gondwana along the Kuunga Orogen between 535 and 510 Ma. The large-scale Adamastor Orogen, consisting of Kaoko, Dom Feliciano, Ribeira, Araçuai and West-Congo mobile belts, also shows broadly similar and symmetric structural architecture throughout. The high-grade thermally softened core partitioned intense wrench dominated strains and networks of transcurrent shear zones that dip inwards with listric form. Either side of the internal zone containing amalgamated arcs and high-grade core, are nappe-fold and thrust belts that rework attenuated passive margin basement and Adamastor Ocean sediments and structures verge outward at moderate to high-angles onto both foreland margins. The Kaoko Belt well illustrates the highly partitioned nature of transpressional systems in general and patterns in common throughout the greater “Adamastor Orogen”; such as metamorphic zonation and heterogeneous distribution of deformation style, flow regime and highly variable degrees of reworking strain and recrystallization. This highly partitioned and steep structural grain localized lithospheric extension and rifting 415 Ma later during breakup and dispersal of Gondwana.
The Western Pacific Triangular Zone (WPTZ) is the frontier of a future supercontinent to be formed at 250 Ma after present. The WPTZ is characterized by double-sided subduction zones to the east and south, and is a region dominated by extensive refrigeration and water supply into the mantle wedge since at least 200 Ma. Long stagnant slabs extending over 1200 km are present in the mid-Mantle Boundary Layer (MBL, 410–660 km) under the WPTZ, whereas on the Core–Mantle Boundary (CMB, 2700–2900 km depth), there is a thick high-V anomaly, presumably representing a slab graveyard. To explain the D″ layer cold anomaly, catastrophic collapse of once stagnant slabs in MBL is necessary, which could have occurred at 30–20 Ma, acting as a trigger to open a series of back-arc basins, hot regions, small ocean basins, and presumably formation of a series of microplates in both ocean and continent. These events were the result of replacement of upper mantle by hotter and more fertile materials from the lower mantle.
We attempt here to correlate the melting phase of major snowball Earth events in the planet with the processes associated with extreme crustal metamorphism and formation of ultrahigh-temperature (UHT) granulite facies rocks. While the dry mineral assemblages that characterize UHT granulites can result from different mechanisms, the direct evidence for the involvement of CO2-rich fluids in generating diagnostic UHT assemblages has been recorded from the common occurrence of pure CO2 fluid inclusions in several terranes. Here we evaluate the tectonic settings under which UHT rocks are generated using modern analogues and show that divergent tectonics—both post-collisional extension and rifting—play a crucial role. In an attempt to speculate the link among CO2 liberation from the carbonated tectosphere, UHT metamorphism and major earth processes, we address some of the important issues such as: (a) how the subcontinental mantle i.e., the tectosphere, had become carbonated; (b) how and when the tectosphere degassed; and (c) what is the difference between Proterozoic orogens and those of the present day. The fate of the Earth as a habitable planet was possibly dictated by a reversal of the fundamental process of formation of oceans through the selective removal of CO2 into mantle in the Hadean times, carbonation of the Archean mantle wedge, and subsequent decarbonation of the carbonated mantle through divergent metamorphism and water infiltration since the Late Proterozoic.