Collisional Orogenesis Research Articles

Continental-scale sediment mixing and dispersal across northern Gondwana: detrital zircon U-Pb-O-Hf isotopic evidence from the Cambro-Ordovician sandstones overlying the Arabian Shield

ABSTRACT The juvenile Neoproterozoic basement of the Arabian Shield is overlain with angular unconformity by a voluminous Cambro-Ordovician cover sequence known as the Saq Formation and Wajid Group. Provenance studies of this vast siliciclastic cover over the Saudi Arabian part of the Arabian-Nubian Shield (ANS) have to date been based solely on U-Pb zircon data and heavy minerals. We present the first combined in-situ U-Pb, δ18O and Lu-Hf isotopic data for detrital zircon from the Saq and Wajid units exposed along the northeastern margin and southern part of the Arabian Shield. U-Pb age spectra reveal prominent age peaks at ca. 0.8–0.55 Ga and 1.1–0.9 Ga with subordinate peaks at ca. 2.2–1.7 Ga and 2.7–2.5 Ga. The δ18O secular variation mirrors global compilations with Archaean zircon defining a restricted δ18O range of ca. 4.0–8.0 ‰ and younger zircon showing wide variation in δ18O up to ca. 14 ‰. The ca. 0.8–0.55 Ga age peak has the largest variation in εHf(t) with about half of all these Neoproterozoic zircon grains being juvenile (εHf(t) > 5), which are interpreted to be sourced from the juvenile terranes of the ANS. Neoproterozoic zircon with evolved εHf(t) signatures require a more distal source beyond the ANS. As extensive ca. 1.1–0.9 Ga crust is lacking in the vicinity of the ANS, the ca. 1.1–0.9 Ga age peak is interpreted to be derived from either contemporaneous orogenic belts in Central Africa or recycled from older sedimentary rocks containing these age components. Extreme variations in δ18O of post – Archaean zircon, together with the evolved εHf(t), indicate crustal thickening and increased incorporation of supracrustal material associated with collisional orogenesis. The remarkable similarities in age spectra and isotopic compositions of the Saq Formation and Wajid Group sandstones with those from other regions in northern Gondwana indicate a continental–scale homogenization and dispersion process.

Genesis and fluid evolution of the Hatu orogenic gold deposit in the West Junggar, Western China

The West Junggar in Xinjiang, western China, represents a significant gold mineralization belt hosting over 200 gold deposits, with the Hatu gold deposit being the largest among them. In this study, ore geology and fluid inclusion assemblages of quartz samples from the Hatu gold deposit were investigated in an effort to clarify the mineralization process and its relationship with the geodynamic settings. The mineralization process is delineated into early (pyrite-albite-quartz veins), middle-a (quartz-ankerite veins), middle-b (quartz-ankerite-sulfide-native gold veins), and late (quartz-calcite veins) stages. The early stage veins suggest a compressional setting while the middle-a and middle-b stage veins suggest a tensional shear setting. The late stage veins are typically filled fissures cutting through earlier veins. Scanning electron microscope-cathodoluminescence (SEM-CL) reveals that early stage quartz (Q1) exhibits concentric CL-oscillatory growth zoning, while middle-a stage quartz (Q2a) displays unidirectional zoning and ranges from CL-bright to CL-dark, middle-b stage quartz (Q2b) is CL-bright and weakly zoned, and late-stage euhedral quartz (Q3) shows sector zoning transitioning from CL-gray to CL-dark. Quartz that formed in these stages developed three types of fluid inclusions: pure CO2 (PC-type), CO2–H2O (C-type), and H2O–NaCl (W-type). The early stage quartz contains C- and W-type fluid inclusions homogenizing at 309–345 °C, while the late stage quartz contains only W-type fluid inclusions with homogenization temperatures of 164–229 °C. Microthermometry of fluid inclusion indicated the evolutionary of the metallogenic fluid from a high-temperature, CO2-rich, and minor CH4 metamorphic fluid to a low-temperature, CO2-poor meteoric fluid. From the early to middle-a stages, fluid boiling caused the unloading of ore-forming elements whereas fluid mixing led to the precipitation of polymetallic sulfides and gold in the middle-b stage. Trapping pressures in the middle-b stage were estimated using C-type inclusions, illustrating that gold mineralization took placed at depth of 8.0 km. We propose classifying the Hatu gold deposit as an orogenic deposit, originating from the collisional orogenesis between the Yili-Kazakhstan and Siberian continents in the Late Carboniferous.

Initial sedimentation after the closure of the Sumdo Paleo-Tethys Ocean: Implications for early Mesozoic tectonics in the East Tethys domain

The closure of the Paleo-Tethys Ocean and subsequent collisional orogenesis in the early Mesozoic played an important role in the formation of the Qinghai–Tibetan Plateau. However, the final closure of the southernmost Paleo-Tethys branching ocean basin in the Qinghai–Tibetan Plateau—known as Sumdo Paleo-Tethys Ocean—and collision between Central and Southern Lhasa terranes remain controversial. In particular, the tectonic significance of early Mesozoic volcanism and sedimentation in the Lhasa terrane is unknown, but crucial for understanding the final stages of ocean closure. Here, we investigate the depositional ages and provenance of detrital zircon in clastic sedimentary rocks, as well as the petrogenesis of the interbedded andesite from the volcano-sedimentary sequence of the Late Triassic to Early Jurassic Xionglai Formation in the Tangjia-Sumdo area. Detrital zircon dates from the Xionglai Formation define five age peaks at 180–200 Ma, 230–340 Ma, 500–620 Ma, 1000–1240 Ma, and 1600–1800 Ma. Detrital zircon trace elements and Hf isotopic characteristics are interpreted to represent derivation from an accretionary wedge and later magmatism related to oceanic slab break-off as well as a minor component from coeval magmatic rocks in the Nyainrong-Nang area in northern Lhasa terrane. Interbedded andesite has a magnesian andesite signature and yields ages of 192–184 Ma with zircon εHf(t) values that range from −3 to +1. We interpret these data as the andesite being sourced from sediment-derived melts that interacted with the overlying mantle wedge in a post-collision extensional setting. Our study suggests that the closure of the Sumdo Paleo-Tethys Ocean and subsequent collision between Central Lhasa and Southern Lhasa terrane may have happened in Late Triassic-Early Jurassic. The final closure of the multi-Paleo-Tethys Ocean and subsequent collision in the Qinghai–Tibetan Plateau may have induced initial subduction of the Meso-/Neo-Tethys Ocean, representing the tectonic transition from collision/post-collision to subduction/accretion in the Qinghai–Tibetan Plateau during the Late Triassic to Early Jurassic.

BOUNDARY BETWEEN THE TIMANIAN AND URALIAN TECTONIC CYCLES: RESULTS OF DATING OF DETRITAL ZIRCONS FROM BASAL HORIZONS OF THE LOWER PALEOZOIC SYNRIFT COMPLEX OF THE POLAR URALS, AND IGNEOUS ROCK AGE DATA REPORT

The Upper Cambrian-Lower Ordovician terrigenous strata, unconformably overlying the Upper Riphean-Vendian rocks of the Timanide orogen in the north of the Urals, and contemporaneous bimodal volcanics and intrusive rocks are considered complexes marking the beginning of rifting which led to the opening of the Paleo-Ural Ocean later on. The article presents the results of U-Pb (LA-ICP-MS) dating of detrital zircons from sandstones lying at the base of the section of the rift complex in the Malaya Usa River basin in the Polar Urals. It was found that the clastic sequence (identified as the Khoydyshor formation) began to accumulate no earlier than the Cambrian–Ordovician transition. Zircon ages fall within the continuous Vendian to Early Ordovician (575–478 Ma) interval with peak at 512 Ma. This age range overlaps with the age of rhyolites interlayered conformably with sandstones and rhyolite porphyry dikes intruding the Khoydyshor formation, thus indicating a possible admixture of products of synsedimentary volcanism. A narrow zircon age pattern allows us to conclude that the main sources of detrital zircons in sandstones were the Early-Middle Cambrian igneous rocks formed at the stage of pre-rift uplift, and, to a lesser extent, the Late Cambrian-Early Ordovician riftogenic magmatic complexes, marking the beginning of the Uralian tectonic cycle, as well as the Late Vendian igneous rocks of the underlying Timanide orogen. Judging by the Th/U ratio, most of the detrital zircons within the sandstones were derived from the Early Paleozoic silicic volcanic and hypabyssal rocks and the Vendian granitoids and diorites. The almost complete absence of older grains, which are typical of coeval sandstones of the northern part of the Urals, may indicate the accumulation of the considered sandstones in a local trough with local clastic material sources. Probability density estimation of U-Pb ages for zircon from igneous and metamorphic rocks of the Polar Urals indicates that there were no gaps in the Late Riphean to Early Ordovician endogenous activity in this region. The main peaks occur at 552, 521 and 500 Ma, and an additional peak – at 665 Ma. The results of dating of detrital zircons from sandstones of the Khoydyshor formation together with the database of U-Pb isotope ages of igneous and metamorphic rocks of the Polar Urals (119 items), compiled by the authors, indicate that the change in geodynamic regime from collisional orogenesis in the Late Vendian to the Early-Middle Cambrian pre-rift uplift and following Late Cambrian rifting was not accompanied by a longterm discontinuity in magmatic activity.

Zircon U-Pb-Hf constraints on the geological evolution of the Bihar Mica Belt, Central Indian Tectonic Zone, and its link to Columbia assembly

In this study, U-Pb-Hf isotope composition and trace element chemistry of zircon from basement gneisses and quartzites of the Bihar Mica Belt (BMB), a belt of supracrustal rocks within the Central Indian Tectonic Zone, is used to constrain crustal growth and reworking. The protoliths of BMB gneisses were emplaced at 1651 ± 5 Ma. The magmas were derived from juvenile and 1747 ± 7 Ma I-type long-lived felsic precursors that survive as xenocrystic cores. Zircon grains from quartzites display two distinct morphologies. Grains with little rounding of edges have internal structures comprising 1750 ± 5 Ma inherited cores mantled by 1657 ± 4 Ma igneous zones that are identical to those from the granite gneisses. The εHf (t) and trace element composition of both the xenocrystic cores and the igneous mantles in these detrital grains are identical to those of zircon in the gneisses. They constitute molasse-like sediments derived from the nearby basement. More rounded grains furnish age clusters between 1857 and 2848 Ma, suggestive of long-distance transport and derivation from multiple sources. In-situ formed metamorphic rims around zircons in gneisses and quartzites furnish 1476–1466 Ma ages, dating the earliest metamorphic overprint. The age of sedimentation is bracketed between 1657 Ma and 1466 Ma. The 1651 ± 5 Ma gneisses and its 1747 ± 7 Ma felsic precursor were I-type, and emplaced in an arc setting. They constitute part of the expansive suite of Paleoproterozoic gneisses of the Chhota Nagpur Gneiss Complex emplaced during protracted period of arc-magmatism between 1.75 Ga and 1.65 Ga. Strongly positive εHf(t) of 2.0–2.85 Ga detrital zircons conforms to the global trend of positive εHf(t) excursions and high dT/dP gradients, and may correspond to passive margin juvenile magmatism associated with the break-up of Archean supercratons prior to Columbia assembly. The 1.86 Ga and 1.75 Ga detrital and xenocrystic zircons from the BMB have enriched εHf(t), in accordance with negative excursions seen in global zircon between 2.0 Ga and 1.70 Ga, reflecting progressive assembly of Columbia through collisional orogenesis. An excursion to strongly positive εHf(t), coinciding with low dT/dP gradients at ca. 1.65 Ga, reflects wide-spread formation of arcs linked to accretionary growth of Columbia.

A Late Triassic gold metallogenic event within the extended tectonic evolution of the West Qinling Orogen, central China: Constraints from U-Pb and Ar-Ar geochronology in the Yangshan gold district

The West Qinling Orogen in central China resulted from Late Devonian to Triassic collisional orogenesis involving accreted terranes along the southwestern margin of the North China Block with subsequent ocean closure and collision of the South China Block with those terranes. The Yangshan gold district, with a pre-mining resource of more than 308 t gold, is situated along the Mianlue Suture Zone on the southern margin of the orogen. The gold orebodies are mainly controlled by the ENE-trending Anchanghe-Guanyinba Fault and its subparallel second-order faults. The relatively low pressure–temperature mineralization is dominated by disseminated pyrite, arsenopyrite, and stibnite hosted in phyllite and granite dikes, accompanied by intense muscovite-silica-carbonate alteration.Four major phases of deformation related to collisional tectonics are recorded in the Yangshan gold district. Early N-S-oriented compressional deformation (D1) is characterized by an alignment of muscovite, overgrowths on framboidal pyrite, and quartz veinlets. D2 is characterized by a series of continuous ENE-trending reverse faults and folds at multiple scales related to SSE-NNW-oriented compression. D3 is related to gold mineralization and is characterized by a series of ENE-trending, largely normal faults, formed during transtensional tectonics. D4 post-dates gold mineralization and is associated with the development of nearly N-S-trending, low-displacement normal faults.New high-precision SHRIMP zircon U-Pb dating of three types of granite dikes in the Yangshan gold district yields broadly coincident ages of 216 ± 3.0 Ma to 210 ± 9.7 Ma, which is a range identical to that of existing dates of 217–211 Ma for more regional granite magmatism in this district. New Ar-Ar dating of gold-related muscovite gives an age of 210.9 ± 1.6 Ma for the Yangshan gold deposit, indicating that hydrothermal activity overlapped or post-dated the final stages of granite intrusion. Pre-226 Ma peak metamorphism of the ore-hosting rocks occurred prior to extensional ductile shear deformation that is constrained by a published 40Ar/39Ar muscovite cooling age of 223 ± 2 Ma. In good agreement, U-Pb constrained ages of retrograde metamorphism and associated late magmatism of around 215 Ma are reported for rocks along the Mianlue Suture Zone.These geological and geochronological data suggest that relatively shallow-level gold mineralization was broadly coeval with Late Triassic transtensional, orogen-parallel deformation along the regional-scale fault system, late in the tectonic evolution of the West Qinling Orogen. This is consistent with its classification as epizonal orogenic gold mineralization.

Prolonged evolution of syn-collisional progressive deformation of the Trans-North China Orogen: Structural and geochronological evidence from the Xiaoqinling region, central China

Significant understanding of the Trans-North China Orogen (TNCO) has been achieved through previous studies. However, the lack of structural analyses, especially for its southern part, has restricted our understanding of the structural evolution of the TNCO. In this contribution, we present new structural and geochronological data from the Taihua Complex of the Xiaoqinling region to reconstruct the collision-induced deformation history and provide constraints on the structural evolution of the TNCO. Paleoproterozoic collision-induced structures in the Xiaoqinling region are characterized by the development of penetrative, ductile deformation fabrics, localized ductile shear zones, and syn-shearing folds, notably sheath folds. The evolution of the folds and syn-tectonic migmatites records the occurrence of non-coaxial progressive shear deformation within ductile shear zones. Vorticity analysis confirms simple-shear-dominated general-shear deformation within the shear zones, with an increase in a pure shear component during the later stages. The integrated results, encompassing the geometry, kinematics, finite strain, and geochronology of these shear zones and folds, reveal the presence of the regional-scale, collision-induced sheath folds that were associated with low-angle thrust shear zones with WNW-directed kinematics. Deformation temperatures of 500–650 °C indicate that the ductile shear zones and simultaneous sheath folds formed during the exhumation process of the TNCO. New zircon U–Pb ages constrain the timing of the metamorphism and ductile deformation to between 1951 and 1840 Ma. Integration of this and previous dating results reveals a history of prolonged collision for the TNCO, lasting from as early as ∼ 1.97 Ga and continuing until as late as ∼ 1.84 Ga, with the earlier period of 1.97–1.88 Ga representing the continental subduction stage and the later period of 1.88–1.84 Ga corresponding to the subsequent exhumation stage. The protracted orogenic evolution for the TNCO supports the notion that large-scale collisional orogenesis can occur over such long durations (over 100 Mya). These structural and geochronological data support the orogenic model of SE-directed subduction polarity.

Geochronological Constraints on the Origin of the Paleoproterozoic Qianlishan Gneiss Domes in the Khondalite Belt of the North China Craton and Their Tectonic implications

The Paleoproterozoic gneiss domes are important structures of the Khondalite Belt in the northwestern North China Craton. However, less attention has been paid to their formation and evolution, and it thus hampers a better understanding of the deformation history of the Khondalite Belt. In this paper, we conducted structural and geochronological studies on the Qianlishan gneiss domes of the Khondalite Belt. The field observations and zircon U–Pb dating results show that the Qianlishan gneiss domes consist of 2.06–2.01 Ga granitoid plutons in the core, rimmed by granulite facies metasedimentary rocks (khondalites) of the Qianlishan Group. Both of them were subjected to two major phases of deformation (D1–D2) in the late Paleoproterozoic. Of these, D1 deformation mainly generated overturned to recumbent isoclinal folds F1 and penetrative transposed foliations/gneissosities S1 at ~1.95 Ga. Subsequently, D2 deformation produced the NW(W)–SE(E)-trending doubly plunging upright folds F2 at 1.93–1.90 Ga, and they have strongly re-oriented S1 gneissosities, giving rise to the Qianlishan gneiss domes. Combined with previous studies, we argue that the Qianlishan gneiss domes were the products of the Paleoproterozoic collisional orogenesis between the Yinshan and Ordos Blocks. Additionally, the development of doubly plunging antiforms is considered an important dome-forming mechanism in the Khondalite Belt.

The consummate geoscientist: a celebration of the career of Maarten de Wit

Abstract This volume assembles a collection of papers on the application of plate-tectonic principles to the understanding of ancient orogens, in honour of Maarten de Wit, who was guided throughout his research career by such applications. There are several recurring themes including: (1) collisional orogenesis associated with supercontinent amalgamation; (2) accretionary orogenesis along supercontinent peripheries; and (3) intracontinental deformation as a consequence of stresses transmitted thousands of kilometres into the orogenic foreland. Very appropriately, given Maarten's huge influence on international cooperation among Earth scientists, 70 authors, from 15 different countries, from every continent except Antarctica, have contributed to the volume.

The Joining of North and South China During the Permian: Coherent Metamorphic Evidence From East Asia Orogenesis

AbstractThe joining of the North and South China blocks marks the formation of the united East Asian continent, which is an integral part of Pangea. The amalgamation of these two continental blocks also resulted in the formation of the world‐class ultrahigh pressure orogenic belt, namely the Dabie–Sulu orogenic belt. Figuring out the time of the initial collision between the two continents is critical for resolving questions such as the duration and the geodynamic processes of the orogeny. A Triassic joining time has been suggested by the geochronology of the eclogite facies rocks in this orogenic belt. However, paleomagnetic and paleontological studies suggested a Permian docking time for these continental blocks. In this paper, we present new metamorphic ages of rocks from northern Dabie and the Permo–Triassic intracontinental orogen of South China, which are all closely associated with this continental collisional event. New age dating results, as well as a synthesis of recent studies on metamorphic rocks occurring in southeastern North China and the Cathaysia Block of South China, show that the onset of the collisional orogenesis along the eastern part of the orogenic belt dates back to the Middle Permian (270–252 Ma). Considering these data and other geological records, we provide a new tectonic model for the major continents of East Asia, in which we show that the initial collision between North and South China occurred in the east during the Middle Permian, and then propagated westward. Continental collisions forming mountains and closing seaways in East Asia thus apparently occurred before the end‐Permian mass extinction, suggesting these paleogeographic changes might have also preconditioned and facilitated the end‐Permian biospheric crisis in the region.

Eclogites and basement terrane tectonics in the northern arm of the Grenville orogen, NW Scotland

The presence of eclogites within continental crust is a key indicator of collisional orogenesis. Eclogites within the Eastern Glenelg basement inlier of the Northern Highland Terrane (NHT) have been re-dated in order to provide more accurate constraints on the timing of collision within the northern arm of the Grenville Orogen. The eclogites yield dates of ca. 1200 Ma which are interpreted to record the onset of continent–continent interaction, and the NHT as a whole is thought to represent the lower plate in successive 1200–1000 Ma collision events. The Eastern Glenelg basement inlier is viewed as a fragment of the leading edge of the NHT continental basement that was partially subducted along a suture and then exhumed back up the subduction channel. Differences in ages of igneous protoliths and intrusive histories, and metamorphic events (this paper) between the NHT basement and the Laurentian foreland, suggests that they were separate crustal blocks until after ca. 1600 Ma. We therefore suggest that: (1) the NHT represents a fragment of Archean–Paleoproterozoic crust that was reworked within the ca. 1.7–1.6 Ga Labradorian-Gothian belt, although whether it was derived from Laurentia or Baltica is uncertain, and (2) amalgamation of the NHT with the Laurentian foreland did not occur until the terminal stages of the Grenville collision at ca. 1000 Ma.

Metamorphic P–T evolution of the pelitic granulites from the Helanshan in the North China Craton revealed by phase equilibrium modeling and garnet trace elements: Implications for Paleoproterozoic collisional orogenesis

Granulite-facies metamorphic rocks are widely exposed in Paleoproterozoic orogens, and their prograde metamorphic evolution is critical for a better understanding of the Paleoproterozoic collisional orogenic and geodynamic processes. In this paper, we present the results of petrology, trace element geochemistry of garnet, P–T conditions calculated by phase equilibrium modeling and garnet trace element geothermobarometry, for the pelitic granulites of the Helanshan Complex in the western Khondalite Belt of the North China Craton (NCC). These results are used for determination of their metamorphic evolution and tectonic implications. Petrographic observations show that the metamorphic evolution of the pelitic granulites can be divided into four stages (M1–M4), and these metamorphic stages are recorded by the mineral inclusions and reaction textures of garnets. Compared with the nearly flat major-element zoning, the zoning of yttrium (Y) and heavy rare earth elements (HREEs) in the garnet cores and mantles show bell-shaped distributions as well as inner-rim troughs and increases on the outer-rims. Different garnets have the same REE patterns in the same textural domain. The bell-shaped distributions of trace elements (Y and HREEs) in the garnets were controlled mainly by Rayleigh fractionation processes under subsolidus conditions, whereas the increases in these elements in the garnet rims were related to the breakdown of major and accessory phases under suprasolidus conditions. By combination of phase equilibrium modeling and garnet trace element geothermobarometry, a complete clockwise P–T path is constructed for the pelitic granulites. This P–T path is characterized by the heating as pressure rising during evolution from early metamorphic stage (M1: 4.2 ± 0.3 kbar/524 ± 17 °C) to peak metamorphic stage (M2-1; 9.8–10.6 kbar /794–815 °C), which is followed by a isothermal decompression (ITD) to the condition of 5.8–6.5 kbar/808–833 °C and later near isobaric cooling (IBC) to subsolidus. As a result, the pelitic granulites revealed that the formation of the Khondalite Belt experienced initially crustal thickening and post collisional extensional uplift. Integrated with previously reported results, the prograde geothermal gradient of the Helanshan pelitic granulites (14 ± 1 °C/km) is similar to that the pelitic schists in the Himalayan Orogen (13 ± 2 °C/km), which suggests that the Paleoproterozoic and present-day orogens have similar geothermal gradient during crustal thickening.

Titanium isotope evidence for the high topography of Nuna and Gondwana - Implications for Earth's redox and biological evolution

Titanium isotopes recorded in glacial diamictites with depositional ages between 2.9 and 0.3 Ga show that the upper continental crust became significantly more felsic relative to the present-day crust during the amalgamation of the Paleoproterozoic Nuna and the Neoproterozoic Gondwana supercontinents. This can be attributed to the continental collisions involved in the assembly of Nuna and Gondwana. The resulting high topographic relief of Nuna and Gondwana orogens must have resulted in an enhanced erosional supply from the continents to oceans. The step changes in the development of organismal complexity from prokaryotes to eukaryotes, and eventually metazoans, appear to be temporally correlated to instances where collisional mountain-building sustained an elevated nutrient supply from the continents to oceans. The nutrient surge associated with the rise of the Gondwana mountains likely provided the necessary impetus for the Neoproterozoic ecological expansion of eukaryotes and the eventual radiation of metazoans. A similar link between the enhanced nutrient supply from Nuna mountains and the radiation of early eukaryotes is plausible, although its mechanistic underpinnings remain unclear. The termination of Nuna orogeny and its transition to Rodinia without significant breakup and subsequent collisional orogenesis corresponds to the long lull in Earth's redox and biological evolution in its middle age.

Insights into the petrogenetic evolution of the Khallari layered intrusion and coeval granites of the Paleoproterozoic Dongargarh Supergroup, Bastar Craton, India

Several layered igneous complexes around the globe host ultramafic-mafic lithologies at the base to more evolved lithologies at the roof sections. In this study, we report U-Pb zircon ages and geochemistry of Paleoproterozoic granites and Khallari layered intrusion from the Dongargarh Supergroup of Bastar craton, central India. The Khallari layered intrusion hosts pyroxenites at the base to more evolved lithologies including gabbro, layered gabbro and anorthositic gabbros towards the roof section of the magma chamber. The estimated weighted mean U-Pb zircon ages of granites (2443 ± 13 Ma) and layered intrusion (2494 ± 19 Ma and 2469.2 ± 5.2 Ma) are in conjunction with the major Siderian crust building peak identified at the craton. The granitic plutons of the Dongargarh Supergroup are chemically similar to post-collisional/anorogenic granitic rocks, in which the rapakivi granites exhibit a fractional crystallization relation with the Khallari layered intrusion. The Dongargarh granites and enclaves were derived by a combination of fractional crystallization and mixing of partial melts from the pre-existing crust of the Bastar craton. Petrogenetic modeling indicates Khallari layered intrusion is formed by the fractional crystallization of lithospheric mantle melt followed by crystal accumulation. The parental melt also experienced localized crustal contamination (up to 10%) during its evolution. The layered intrusion and the granites formed in a post-collisional rift setting where magmatism postdates the proposed subduction and collisional orogenesis at 2.5 Ga involves cratonic domains of Eastern and Western Bastar cratons.

Metallogeny in the Bangong–Nujiang belt, central Tibet, China: A review

The Bangong–Nujiang metallogenic belt consists of scattered Tethyan oceanic blocks, mainly distributed underneath the margins of the Qiangtang and Lhasa terranes in central Tibet. A new world-class metallogenic belt has been reported in this region recently, based on the geological mapping and ore deposit prospecting over the last two decades. It currently comprises inferred resources of 30 Mt Cu and 500 t Au, together with several Cr–Ni, Fe, and W (Mo) resources, forming a significant potential area for future mineral exploration. These metals are mainly hosted in porphyry copper, skarn copper, skarn iron, orogenic gold, quartz-vein tungsten, and ophitic chromite deposits. The mineral deposits in the Bangong–Nujiang metallogenic belt have been widely recognized in different localities, including the southern edge of the southern Qiangtang block, part of the north Lhasa block, and even part of the central Lhasa block, indicating they were formed in variable geological settings, from the initial opening, subduction, and collision to the extension of the Bangong–Nujiang Ocean. Specifically, five major tectonic events contributed to mineralization, including the stage 1 (240–165 Ma) initial opening of the Bangong–Nujiang Ocean, stage 2 (165–145 Ma) oceanic subduction, stage 3 (145–100 Ma) close of the ocean, stage 4 (100–65 Ma) continent–continent collisional orogenesis, and stage 5 (65–0 Ma) post-orogenesis. At stage 1, Cr–Ni deposits were formed during the initial opening of the ocean; porphyry–epithermal Cu (Au), skarn Fe, and minor orogenic Au deposits were formed at stage 2 and stage 3; a younger pulse of a few porphyry–skarn Cu ± Mo and orogenic Au deposits were formed during stage 4; finally, W(Mo) deposits were generated in stage 5. In general, porphyry Cu systems, orogenic Au, and skarn Cu polymetallic deposits that occurred in the subduction and post-collision settings related W(Mo) deposits have the most potential for future exploration. An in-depth investigation of several scientific problems, such as addressing the tectonic setting, magmatism, and metallogeny of this region and genetic linkage of these deposit preservations to plateau uplift, is essential for the future success of exploration in the Bangong–Nujiang metallogenic belt.

Accretionary orogenesis triggered by collision across continent distance: Evidence from the Proto‐Tethyan West Kunlun, China

AbstractProto‐Tethyan orogenic processes prior to the late Ordovician collision remain unclear. Both whole‐rock La/Yb‐ and zircon Eu/Eu*‐based crustal thickness proxies along with petrological and geological observations were used to reconstruct mountain‐building history for the West Kunlun orogenic belt, China, over the span of Early Palaeozoic. Here, we demonstrate that Proto‐Tethyan West Kunlun crust has observed significant accretionary orogeneses at 520–480 Ma and 480–450 Ma and collisional orogenesis at 450–400 Ma. The 520–480 Ma accretionary orogenesis in West Kunlun together with the coeval Delamerian accretionary contractional orogenesis in eastern Australia were simultaneously induced by continent‐continent collisions that welded the Gondwana landmass. Ca. 440 Ma docking of Tarim and its eastern neighbouring blocks along the northern margin of Gondwana in turn triggered the Lachlan accretionary orogenesis along the opposite margin. This study highlights that accretionary orogenesis could be a manifestation of far‐field compressional stress from continent‐continent collision.

Advantages and Limitations of Combined Diffusion-Phase Equilibrium Modelling for Pressure–Temperature–Time History of Metamorphic Rocks

ABSTRACT This paper presents and discusses the results of phase diagram (Perple_X) and diffusion modelling (CZGM, or Compositional Zoning and its Modification by diffusion) to constrain the P–T path of metamorphism. The approach is based on the best fits between the zoning profile in measured garnet and that obtained by the intersections of garnet isopleths calculated by phase diagram modelling using whole rock bulk composition. The model was applied to garnets in natural rocks of various metamorphic grades, which were formed within different geotectonic environments. To compare the sequence of compositional change during Barrovian-type metamorphism, well-studied pelitic rocks from garnet–staurolite, kyanite–sillimanite, and sillimanite-K-feldspar metamorphic zones were selected. Garnets with two-stepped core and rim profiles that were formed during two different metamorphic stages or events were used for pressure–temperature (P–T) path constraint of each stage or event. For high-grade rocks, in which the original zoning profile in garnet was severely modified, the diffusion of the initial zoning profile was quantified to estimate the timescale of the metamorphic event. These rocks include high- to ultra-high-pressure rocks, which were subjected to thermal overprinting during collisional orogenesis. The results of the application of this approach allow for deciphering the reason why the calculated profile by phase diagram modelling does not fit with that of the measured garnet from low-grade rocks, in which garnet has preserved the original compositional zoning. This includes garnets whose nucleation was shifted from the garnet-in boundary to higher temperatures and pressures, as well as garnet crystallised during different metamorphic stages or events. Finally, the P–T paths in high-grade rocks were constrained after the multicomponent diffusion in garnet was quantified, and this was used for further P–T-time path constraint of metamorphism in the rocks.

Episodic provenance changes in Middle Permian to Middle Jurassic foreland sediments in southeastern Central Asian Orogenic Belt: Implications for collisional orogenesis in accretionary orogens

The final collisional orogenesis in accretionary orogens is crucial for reconstructing the whole orogenic circle and understanding the material and energy recycling along convergent margins. However, it is always not straightforward to be addressed, particularly when the final suturing following the ocean closure occurred softly, for instance, the Central Asian Orogenic Belt (CAOB). In this study, a comprehensive dataset of detrital zircon U-Pb ages and Hf isotopes for the Middle Permian to Middle Jurassic foreland sediments from the Linxi region, southeastern CAOB, is synthesized. We observed multiple abrupt changes in sedimentary provenance over time from this dataset: (1) the ca. 275 Ma sediments (Upper Zhesi Fm.) were entirely sourced from the local NAO, whereas the ca. 270–258 Ma sediments (Middle-Upper Linxi Fm.) received an additional detritus contribution from the northern NCC, (2) the ca. 257–236 Ma sediments (Lower-Middle Xingfuzhilu Fm.) returned to a pure NAO source, but the slightly postdated ca. 227 Ma sediments (Upper Xingfuzhilu Fm.) show provenance affinities of both NAO and northern NCC, (3) the ca. 171 Ma sediments (Middle Xinmin Fm.) were exclusively derived from the Late Paleozoic to Early Mesozoic magmas in the NAO and northern NCC with no Early Paleozoic and Precambrian detritus. The above episodic shifts in sedimentary provenance observed in the Linxi region, in conjunction with other regional geological evidence, provide key constraints on the pre- to post-collisional evolution in the southeastern CAOB, including the transition from waning subduction to initial collision, subsequent slab break-off and intracontinental contraction, and the post-collisional extension before the superposition of the Paleo-Pacific tectonic regime. Our results show that understanding the spatio-temporal changes of sedimentary provenance of the foreland basins systems during the plate convergence and orogenic evolution can aid in exploring the final collisional dynamics and evolutionary history in ancient accretionary orogens.

Metamorphic P–T Evolution and In Situ Biotite Rb–Sr Geochronology of Garnet–Staurolite Schist From the Ramba Gneiss Dome in the Northern Himalaya

The North Himalayan gneiss domes provide a window for looking into the deeper crust and record abundant clues of continent collisional orogenesis. This study carried out detailed petrology, in situ LA–ICP–MS biotite Rb–Sr dating, and phase equilibrium modeling on garnet–staurolite–two-mica schist in the Ramba gneiss dome in order to constrain metamorphic P–T evolution and the timing of metamorphism. A clock-wise P–T path, involving an early prograde process that evolves from ∼540°C at ∼4.4 kbar to ∼630°C at ∼6.0 kbar, was constructed for garnet–staurolite–two-mica schist in the Ramba gneiss dome. In situ LA–ICP–MS biotite Rb–Sr analysis yielded two metamorphic ages of 37.17 ± 5.66 and 5.27 ± 3.10 Ma, corresponding to the timing of retrograde cooling and the cooling age of the dome following the thermal resetting by the emplacement of ca. 8 Ma leucogranite pluton in the core of the dome, respectively. The peak metamorphism is inferred to be older than ca. 37 Ma. Based on these results and the data previously published, the garnet–staurolite–two-mica schist recorded the Eocene crustal thickening, following the India–Asia collision and later the exhumation process.

Shear-wave velocity structure of upper mantle along the Zagros collision zone

The lithosphere beneath the Zagros and central Iran has sustained long-lasting Neo-Tethyan subduction and subsequent collisional orogenesis, leading to the complicated crustal and lithospheric structure beneath the Iranian plateau. To better understand the geotectonic and geodynamic evolution of the Iranian plateau, we estimate the shear-wave velocity structure along profiles perpendicular to the Zagros using a self-parameterized Bayesian inversion of the Rayleigh wave group velocity dispersion curves in the period range of 5 to 120 s. Our velocity models, in line with a segmented slab model, show that different geodynamic processes have dominated along the Zagros. In the northern Zagros, the thick and high-velocity lithosphere beneath the Sanandaj-Sirjan Zone (SSZ) and Urumieh-Dokhtar Magmatic Arc (UDMA) is abruptly separated from the low-velocity lithosphere beneath central Iran, while the high-velocity anomaly underlies the UDMA and central Iran in the central and southern Zagros. We propose that the Arabian lithosphere near the suture has probably experienced a distributed thickening in the northern Zagros, and it underthrusts beneath central Iran in the central and southern Zagros. In the central and southern Zagros, a high-velocity anomaly elongates at a depth of 80–120 km between the low-velocity lithospheres of the UDMA and Lut block. This suggests that flat-slab subduction has not extended to the east of the Iranian plateau, therefore, the Eocene-Oligocene flare-up magmatism in the Lut block may be directly independent of the Neo-Tethys subduction. This study suggests that lateral tearing might be responsible for the slab detachment beneath the central and southern Zagros. The slab lithosphere may have started to tear from beneath the central UDMA and have propagated to the edges since ~10 Ma. Furthermore, the southeasternmost Zagros in the vicinity of the Makran zone, as a corner continental collision, has probably experienced slab tearing and break off during the Middle-Late Miocene.