Search

The Lesser Xing'an—Zhangguangcai Range of northeast China is located in the eastern segment of the Central Asian Orogenic Belt (CAOB), which records intense magmatism during the Mesozoic. The petrogenesis and geodynamic setting of the Early Jurassic intrusive rocks in this region are unclear. In this paper, we present new zircon U–Pb age and whole-rock geochemical data for these intrusive rocks to investigate their origins and tectonic setting. Zircon U–Pb dating suggests these intrusive rocks were emplaced during the Early Jurassic (197–187 Ma). The granites are enriched in silica and alkali, and depleted in MgO and CaO. They are metaluminous to weakly peraluminous, and have high A/CNK values and low zircon saturation temperatures (TZr ~ 779°C), suggesting they are highly fractionated I-type granites derived by partial melting of lower crustal materials. The granites exhibit negative Nb, Ta, P, Eu, and Ti anomalies due to fractional crystallization. The diorites and gabbros have low SiO2 contents and high Mg# values, and are enriched in light rare earth and large-ion lithophile (Ba, K, and Sr) elements, and depleted in heavy rare earth and high field strength (Nb, Ta, and Ti) elements. The geochemical characteristics show that the mafic magmas were derived by partial melting of mantle that had been metasomatized by subduction-related fluids. Based on the geochemical characteristics of coeval intrusive rocks and the regional geological setting, we suggest the Early Jurassic intrusive rocks in the Lesser Xing'an—Zhangguangcai Range were formed along an active continental margin, possibly as a result of bidirectional subduction of the Mudanjiang Oceanic plate between the Jiamusi and Songnen—Zhangguangcai Range massifs. [ABSTRACT FROM AUTHOR]

This article presents the results of U–Pb (ID-TIMS) geochronological, geochemical, and Sm–Nd isotopic-geochemical studies of metavolcanic rocks of the Djagdagle Formation, which belong to the key elements of the Bureya continental massif. It was established that the age of metavolcanic rocks of the Djagdagle Formation is 217 ± 7 Ma and corresponds to the Late Triassic. This fact contradicts the traditional ideas, according to which the Djagdagle formation is the Early Precambrian in age. The results of Sm–Nd isotope studies of the metavolcanic rocks indicate the melting of rocks of continental crust with Paleoproterozoic model ages during the formation of initial melts. The new geochronological data and previously published data allow us to distinguish at least two stages of magmatic activity in the Triassic within the northwestern part of the Bureya massif: ~243 and 219–201 Ma. On the basis of synchronous of Neoproterozoic, Early Paleozoic, Late Paleozoic, and Early Mesozoic magmatic events in the geologic history of the Bureya and Songnen–Zhangguangcai Range massifs, an assumption about their common geological history at least since the Late Neoproterozoic has been proposed. The close spatial position of metavolcanic rocks of the Djagdagle Formation and the Mongol–Okhotsk Orogenic Belt, their Late Triassic age (217 ± 7 Ma), and geochemical features allow us to link the formation of initial melts of metavolcanic rocks of this formation with within-plate magmatism in the rear part of subduction zone of the Mongol–Okhotsk Ocean beneath the northern (in modern coordinates) margin of the Bureya continental massif. [ABSTRACT FROM AUTHOR]

The geologic evolution of the Gondwanide orogen recorded during the late Palaeozoic along the Panthalassan border of Gondwana is related to an active continental margin, though it is still debatable whether it was built by collision or accretion. To disentangle its orogenic processes and provide constraints on the orogen type, we characterize the physicochemical conditions of metamorphism and associated deformation of the Mina Gonzalito Metamorphic Complex from northern Patagonia (41°28’30” S-65°40’30” W). New field mapping and comprehensive petrochronologic analysis constrain the evolution of a thick-skinned fold and thrust belt in a retroarc setting, which is spatially and temporally related to the geometry and kinematics of the right-lateral reverse El Jagüelito ductile shear zone. Metamorphic evolution resulted in a clockwise P‐T‐t-D path reflecting three stages of continuously changing P-T conditions under high-pressure (8.0–9.9 kbar) amphibolite facies (540–680°C) during a single-phase progressive ductile deformation event. Monazite ages ranging from 303 ± 5 to 252 ± 6 Ma account for the single-phase regional tectono-metamorphic event spanning ~ 50 My. Our results, integrated with regional data, led to interpreting the late Palaeozoic Gondwanide orogen developed along the Panthalassan margin of Gondwana as accretionary in advancing-mode. [ABSTRACT FROM AUTHOR]

Integrated geochemical, U-Pb zircon, and Pb isotopic data from granitoids of the Wulandele porphyry molybdenum deposit, northeastern Inner Mongolia, are reported to disclose the possible magmatic process and Mo ore-forming process. LA-ICP-MS zircon U-Pb dating constrains the timing of the quartz diorite and monzonitic granite to 282 ± 2.4 Ma and 135.4 ± 2.1 Ma, respectively. The ages are accordant with geological facts which state that the shallow Permian granitoids are only the ore-hosting rock while the concealed Cretaceous fine-grained granite is the causative intrusion. Whole-rock geochemical data show that the granitoids belong to the high-K calc-alkaline series, and are enriched in LILEs, but depleted in HSFEs. Permian granitoids exhibit I-type characteristics, while Cretaceous granite is akin to A-type granite. Pb isotopic ratios are consistent between Permian granitoids and Cretaceous granite with ratios of 206Pb/204Pb = 18.048–18.892, 207Pb/204Pb = 15.488–15.571, and 208Pb/204Pb = 37.066–38.441. Considering geological and geochemical features together, Permian granitoids are interpreted as subduction-related continental margin high-K calc-alkaline rocks, while Cretaceous granite may be the result of the remelting of the relic Permian arc in an extensional environment induced by the rollback of the Paleo-Pacific plate. Different from classical porphyry-type deposits, the Wulandele Mo deposit, which formed in an intraplate tectonic setting, indicates that the intraplate porphyry Mo deposit should be one of the important exploration targets in the Central Asian Orogenic Belt, especially its eastern segment. [ABSTRACT FROM AUTHOR]

Continental subduction is the major cause of regional heterogeneities in the lithospheric mantle and contrasting types of magmatism and mineralization in post-collisional settings. We illustrate the relation between the nature of the subducted crust and the character of magmatism for the Late Miocene New Guinea Orogen that formed by the collision of the Australian continental margin with an island arc. The bipartite nature of the subducted Australian plate margin, with Precambrian crust in the west and Phanerozoic accreted arcs in the east, is reflected in the contrasting magmatism along the strike of the New Guinea Orogen. The chemical signature of the subducted crust is particularly prominent in small-volume Late Miocene–Quaternary ultrapotassic rocks of New Guinea. In the west, ultrapotassic lavas have low εNd values (−12.6 to −20.9), indicating the recycling of ancient continental material. Conversely, high εNd values of +3.5 to +4.5 are found in ultrapotassic lavas from eastern New Guinea. This suggests recycling of juvenile continental material, similar to the orthogneisses exposed in the Late Miocene ultrahigh-pressure metamorphic complex of the D'Entrecasteaux Islands. By comparison with ultrapotassic rocks from other orogenic belts, we show that crustal recycling is responsible for regionally contrasting redox conditions in the lithospheric mantle, which may explain why porphyry-type deposits are important in some regions but absent in others. [ABSTRACT FROM AUTHOR]

Characterizing neotectonic activity along mountain fronts in active orogens is the key to better understanding trajectories of landscape evolution, climatic‐tectonic couplings and natural hazards. One such prominent mountain front is the Western Andean Front (WAF), which defines the boundary between two main physiographic units along the Chilean Andes (15°S to 39°S): the Central Depression and Principal Cordillera. This study analyses the geomorphic imprints of neotectonic fault activity in the WAF between 35°S and 37°S. We used several topographic metrics, including the mountain‐front sinuosity index (Smf), the valley floor width‐to‐height ratio (Vf) and the stream length‐gradient (SL) index to gain information about the regional distribution of deformation patterns and its relative tectonic activity for distinctive segments. In addition, a raster map combining rock strength (RS) and mean annual precipitation (MAP) allowed discriminating lithology‐climate vs. tectonics influence on SL anomalies from catchments spanning from the main deformation zone to the regional drainage divide. We use the local relief and swath profiles to quantify the incision and transient state of mountain fronts to evaluate the geomorphic response to tectonic and/or climatic input. Our analysis highlights significant variations from north to south, delineating two distinct segments with different topographic, geomorphic and geometric fault characteristics. These segments are indented at approximately 36°S. From north to south, there is a segment with an inactive thrust front with a primarily climate‐driven fluvial response over long timescales and a second segment with a transient state adjusting to relatively high uplift rates. Morphometric data analysis, DEM‐based morpho‐structural maps, geological maps and previous research support the interpretation of two sets of neotectonic faults: (1) NNE‐striking reverse faults with a dextral slip component and (2) NW‐striking sinistral slip faults, likely a response to deformation partitioning caused by oblique subduction on a continental margin. [ABSTRACT FROM AUTHOR]

The subcontinental lithospheric mantle (SCLM) is now suggested by many workers to play a role in the formation of orogenic gold deposits in active continental margins, given that the gold and volatiles may be introduced into the SCLM during plate subduction. The giant Cretaceous Jiaodong gold province within the North China block occurs in a convergent margin setting where there is no terrane accretion, thus eliminating from consideration the commonly accepted metal and fluid source reservoir for orogenic gold--the metamorphosed upper crust of an active orogenic belt. Thus, the auriferous fluids were released below the high-grade Archean cratonic rocks from either enriched SCLM or directly from the subducted oceanic slab. Mercury (Hg) isotopes allow fingerprinting of isotopically distinct reservoirs, discriminating between the two possibilities. We present Hg isotope data for a set of pyrite grains, native gold, and lamprophyres from six main gold districts in the Jiaodong gold province. These samples dominantly yielded near-zero Δ199Hg (0‰ ± 0.1‰), within uncertainty of the mantle Δ199Hg value. The results provide novel evidence that the SCLM predominantly controlled the Hg budget of the Jiaodong gold deposits, implying that the SCLM acted as a buffer for the crustal mass-independent fractionation Hg signatures and a storage reservoir for gold and volatiles. Consequently, during slab subduction, gold and volatiles were recycled and stored within the SCLM and were later released from the mantle during uplift and relaxation of compressional tectonics. [ABSTRACT FROM AUTHOR]

This paper aims to update our understanding of the carbon cycle in the Himalayas, the most intense collisional orogeny globally, by providing new insight into its impact on Cenozoic climate cooling through the use of isotopic variations in both organic and inorganic carbon and an isotopic mass balance model. Our results from 20 selected hot springs show that the relative contributions of dissolved carbon from the mantle, metamorphic decarbonization, aqueous dissolution, and soil organic matter are approximately 2%, 82%, 6%, and 10%, respectively. Approximately 87% ± 5% of CO2 generated in the deep crust precipitates as calcite, while approximately 5.5% ± 1% of this carbon is converted to biomass through microbial chemosynthesis at depths less than 2 km. Our random forests approach yielded a metamorphic carbon flux from the entire Himalayan orogenic belt of approximately 2.7 ∼ 4.5 × 1012 mol/yr. The minor CO2 released into the atmosphere (2.5 ∼ 4.2 × 1011 mol/yr) is comparable to the carbon consumption driven by Himalayan weathering. This paper provides new insights into deep carbon cycling, notably that approximately 93% of deeply sourced carbon is trapped in the shallow crust, rendering orogenic processes carbon neutral and possibly acting as one of the major triggers of long‐term climate cooling in the Cenozoic. Plain Language Summary: Large‐scale deep metamorphic decarbonization and CO2 release into the atmosphere during continental collision orogenesis worldwide have had significant impacts on Cenozoic global climate change. However, the carbon sources and sinks and the mechanisms underlying their impacts on climate change are not fully understood. This paper reports the chemistry of aqueous solutions, carbon isotopic compositions of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC), and helium and carbon isotopic compositions of free gases from hot springs in southern Tibet. The carbon isotope fractionation model between gas and aqueous solutions revealed that the carbon released from depth underwent six different stages. Based on the random forests machine learning algorithm, we estimated the metamorphic carbon flux across the Himalayan orogenic belt. Furthermore, only a small fraction (7%) of deep carbon is eventually released into the atmosphere, and this volume is the same magnitude as the amount of carbon absorbed by silicate weathering on the Tibetan Plateau. This paper emphasizes that the carbon sequestration process in the upper crust may have resulted in nearly carbon‐neutral geological bodies in the Himalayan orogenic belt, thus playing a critical role in Cenozoic climate cooling. Key Points: Approximately 87% of deeply sourced carbon precipitates as calcite, while approximately 5.5% is sequestered as biomass in the shallow crustThe carbon flux across the Himalayan orogenic belt was estimated by the random forests approachCrustal thickening has attenuated long‐term deep carbon emissions from the Himalayas [ABSTRACT FROM AUTHOR]

The giant Verkhoyansk-Kolyma gold province, producing more than~ 3700 t of gold, is one of the most important metallogenic provinces for orogenic gold deposits in the world. The province is located on the eastern margin of the Siberian craton. The main types here are multistage orogenic Au-As and orogenic-like Au-Sb types of mineralization, related to the Late Jurassic-Early Cretaceous metallogeny and the evolution of the convergent margin. These deposits were formed in the environment of late orogeny during two metallogenic stages -- the Late Jurassic-Early Cretaceous collision-related (early stage/stage one, 135-150 Ma) and the Early Cretaceous subduction- related (late stage/stage two 114-130 Ma). The common features, differences and genetic nature of the deposits of these two metallogenic stages have been debated for a long time. To improve the understanding of these problematic issues and the genesis of deposits, and control over them by the mantle lithosphere, we consider here the Early Cretaceous orogenic belts of the eastern margin of the Siberian craton. Orogenic belts are related to the development of the paleo-Arctic and paleo-Pacific margins of Siberia. The tectonic, geochronological, mineralogical and geochemical specificity of the deposits of the orogenic belts are shown. A regional metallogenic overview of gold deposits is performed using data on the age of mineralization and the isotopic composition of sulfur sulfides. A preliminary model of the origin of late stage mineralization is proposed in connection with the processes of the Okhotsk-Koryak orogenic belt formation. Increased concentrations of siderophilic and chalcophilic elements, the Ni, Bi minerals presence in the ores, relatively high fineness of gold, predominance of juvenile sulfur in the isotopic composition of sulfide sulfur, and the control by large trans-crustal faults as well as spatial and chronological association with initial (dike) magmatism indicate mantle sources of ore fluids. This mineralization within the orogenic belts of the eastern margin of the Siberian craton assumingly appeared due to dehydration of the submerged slab and local upwelling in the mantle in the rear of the active continental margin. The possibility of the gold-bearing fluids existence in such conditions is estimated. The metallogenic specific nature of coiiision-reiated and subduction-reiated orogenic Au is defined. The proposed modei can be useful for the analysis of poiychronous orogenic Au-As and orogenic-iike Au-Sb metaiiogeny of orogenic beits on craton margins giobaiiy. [ABSTRACT FROM AUTHOR]

The Cenozoic Alpine, and Paleozoic Variscan and eo-Variscan collisional belts are compared in the framework of the Wilson cycle considering differences between cold and hot orogens. The W. Alps result of the opening and closure of the Liguro-Piemonte ocean, whereas the Paleozoic Eovariscan and Variscan orogenies document multiple ocean openings and collisions in space and a polyorogenic history in time. Jurassic or Early Ordovician break-up of Pangea or Pannotia megacontinents led to the formation of passive continental margins, and the opening of Liguro-Piemonte, or Rheic, Tepla-Le Conquet, andMedio-European oceans, respectively. In Paleozoic or Mesozoic, microcontinents such as Apulia and Sesia or Armorica and Saxo-Thuringiawere individualized. The oceanic convergence stage was associated with the development of arcs and back-arc basins in the Variscan belt but magmatic arcs are missing in the W. Alps, and inferred in the Eo-variscan one. Though the nappe stack is mainly developed in the subducted European or Gondwana crust in the western Alps and Eo-variscan cases, the Moldanubian nappes formed in the upper plate in the Variscan case. The Alpine and Variscan metamorphic evolutions occurred under ca. 8 °C/km and 30 °C/km gradients, respectively. During the late- to post-orogenic stages, all belts experienced "unthickening" accommodated by extensional tectonics, metamorphic retrogression, and intramontane basin opening. The importance of crustal melting, represented by migmatites, granites, and hydrothermal circulations in the Variscan and Eo-Variscan belts is the major difference with the W. Alpine one. The presence, or absence, of a previous Variscan or Cadomian continental basement might have also influenced the rheological behavior of the crust. [ABSTRACT FROM AUTHOR]

The northern South China Sea (SCS) margin evolved from the Mesozoic convergent to Cenozoic divergent continental margin, and thus, it developed on a heterogeneous crystalline basement with inherited Mesozoic structures. Pre-existing structures and their interactions with rift faults have historically not been described or interpreted in the intensely stretched Baiyun sub-basin. Large-scale 3D seismic reflection data allow us to identify four types of Mesozoic tectonic fabrics within the basement and explain their genesis: (1) Thin, isolated and north-dipping seismic reflections 1, interpreted as thrust faults representing orogenic processes. Tilted thick seismic reflections 2 are formed by reactivation of seismic reflections 1 during post-orogenic extension, which are all related to the NW-ward subduction of the palaeo-Pacific plate. (2) Thin, isolated and shallowly dipping seismic reflections 3 and low-amplitude, semi-transparent and chaotic seismic reflections 4 represent the low-angle thrust system and the associated nappe units, which are related to the shift from NW-to NNW-ward subduction of the paleo-Pacific plate. Subsequently, we investigate the structural interaction between Mesozoic intra-basement and Cenozoic rift structures. Syn-rift, post-rift and long-term faults are developed in Cenozoic strata, and quantitative statistical and qualitative analyses revealed two main types of structural interactions between them and underlying intra-basement structures: (1) Rift faults develop with inheritance of intra-basement structures, including fully and partially inherited faults. (2) Rift faults modify intra-basement structures, although they are controlled by intra-basement structures at an earlier stage. Finally, our results reveal the control of pre-existing structures on the geometry of the Baiyun sub-basin, especially the selective reactivation of NE-trending shear zones (SR2), which are influenced by the regional stress field and the width and dip of the shear zones. [ABSTRACT FROM AUTHOR]

New geochemical data and radiometric ages of the protoliths of variably reworked metamafic (granulites and gabbros) and felsic rocks (orthogneisses) from the Cabo Ortegal allochthonous Complex are presented. Their igneous precursors were emplaced in ensialic environments and exhibit geochemical signatures transitional to tholeiitic character, probably originating in arc settings (with continental and oceanic components and minor crustal recycling). The new geochronological results (encompassing the Miaolingian and Furongian epochs of the Cambrian) link the aforementioned scenarios to a Cadomian magmatic arc. The 505Ma protoliths of calc-alkaline orthogneisses and mafic granulites would be the oldest in the sequence of intrusion events. The latter and the 498–486Ma protoliths of gabbros (emplaced in sedimentary host sequences later transformed into Variscan high-pressure and intermediate-pressure gneisses) can be considered as snapshots of the ongoing continental arc evolution. The 498–486Ma gabbro intrusives of these gneisses, together with the 505–503Ma orthogneisses, are ascribable to palaeo-geographically separate scenarios before the Variscan amalgamation of their country rocks. They would expand the initiation of rifting of the Gondwana continental margin to the Miaolingian Cambrian epoch. It is inferred that the Cadomian continental-arc (active at least since 750Ma) experienced in the 510–460Ma interval the consequences of a vanishing active subduction. Certain domains flanking the arc underwent forearc sedimentation and deformation, whereas others were affected by an increasing extension (rifting) and/or back-arc basin formation. The latter marked the initiation of the beginning of a Wilson Cycle, which ended in the late Palaeozoicwith the formation of the Variscan interior orogenic belt. [ABSTRACT FROM AUTHOR]

Hydrothermal mineralization along the circum-Pacific continental margin is genetically linked to the motions of the Pacific Plate. Compiled geochronological results of ore deposits, coupled with the newly reconstructed geometry of the late Early Cretaceous subduction zones in East China, North America, and the Central Andes using GPlates and I2VIS software, were applied to investigate the relationships between mineralization and Pacific Plate formation. The ~120-m.y.-old orogenic Au provinces in East China and North America are related to transpression caused by high-rate oblique subduction with intermediate--high dip angles of the Izanagi and Farallon plates, respectively. In contrast, the ~105-m.y.-old porphyry-epithermal belt in Southeast China was produced by oblique subduction of the Izanagi Plate with low--intermediate subduction rates and intermediate--high dip angles. In the Central Andes, the oblique subduction of the Farallon Plate with low--intermediate rates and low dip angle accounted for iron oxide--copper--gold ore (IOCG) deposit mineralization in South Peru at ca. 110 Ma; whereas the high rate and low dip-angle subduction of the paleo-Phoenix Plate, which caused mild compression, was responsible for Fe, porphyry Cu, and IOCG mineralization in North Chile at ca. 110 Ma. The late Early Cretaceous metallogenic response in the circum-Pacific region coincides with superplume events that triggered the significant growth of the modern Pacific Plate. The forward simulations reveal that different subsequent styles of subduction and associated magmatism are likely responsible for the distinct mineralization types present in the region, including orogenic Au, porphyry-epithermal, Fe, and IOCG deposits. The precise dynamics of the subduction zone determined by this study led to the improved metallogenesis models in the Pacific margin. [ABSTRACT FROM AUTHOR]

There is general agreement that a series of East Asian blocks has always lain outboard of both India and Australia along the North Indo--Australie peripheral orogen. However, whether the East Asian blocks were involved in the interior orogens of East Gondwana remains equivocal. The geochronology and geochemistry of Neoproterozoic--Late Triassic rocks in the Russian Far East, together with existing paleontological and detrital zircon data, offer an opportunity to determine the tectonic origin and drift history of the Bureya--Jiamusi--Khanka superterrane. Biotite and amphibole 40Ar/39Ar dating results define a distinctive episode of Late Pan-African (ca. 550 Ma) metamorphism and a local Late Triassic (ca. 219-200 Ma) episode of deformation for the Bureya--Jiamusi--Khanka superterrane. Zircon U--Pb ages and whole-rock geochemical data indicate that the Early Ordovician (483 ± 3 Ma) highly fractionated I-type monzogranites were emplaced in a post-collisional setting linked to the collapse of a Late Pan-African orogen, while the Late Triassic (ca. 234-223 Ma) A-type quartz syenites and I-type granite aplite dikes were formed in a slabpull--induced passive continental margin of the subducting Mudanjiang oceanic plate. These crucial archives, complemented by data from the literature, reveal that the Bureya--Jiamusi--Khanka superterrane made up the northernmost Kuunga-Pinjarra interior orogen during the final assembly of East Gondwana. As a result of Devonian rifting after Early Ordovician orogen collapse, the Bureya--Jiamusi--Khanka superterrane escaped from the Kuunga-Pinjarra interior orogen and subsequently migrated to Northeast Asia by the Late Triassic to Jurassic due to the subduction and closure of the Paleo-Tethys and Paleo-Pacific oceans. [ABSTRACT FROM AUTHOR]

In this paper, the Hellenic orogenic belt's main geological structure and architecture of deformation are presented in an attempt to achive a better interpretation of its geotectonic evolution during Alpine orogeny. This study was based not only on recent research that I and my collaborators conducted on the deformational history of the Hellenides but also on more modern views published by other colleagues concerning the Alpine geotectonic reconstruction of the Hellenides. The structural evolution started during the Permo–Triassic time with the continental breaking of the supercontinent Pangea and the birth of the Neotethyan ocean realm. Bimodal magmatism and A-type granitoid intrusions accompanied the initial stages of continental rifting, followed by Triassic–Jurassic multiphase shallow- and deep-water sediment deposition on both formed continental margins. These margins were the Apulian margin, containing Pelagonia in the western part of the Neotethyan Ocean, and the European margin, containing continental parts of the Serbo-Macedonian and Rhodope massifs in the eastern part of the Neotethyan ocean. Deformation and metamorphism are recorded in six main deformational stages from the Early–Middle Jurassic to the present day, beginning with Early–Middle Jurassic Neotethyan intra-oceanic subduction and ensimatic island arc magmatism, as well as the formation of a suprasubduction oceanic lithosphere. Compression, nappe stacking, calc-alkaline magmatism, and high-pressure metamorphic events related to subduction processes alternated successively over time with extension, orogenic collapse, medium- to high-temperature metamorphism, adakitic and calc-alkaline magmatism, and partial migmatization related to the uplift and exhumation of deep crustal levels as tectonic windows or metamorphic core complexes. A S- to SW-ward migration of dynamic peer compression vs. extension is recognized during the Tertiary Alpine orogenic stages in the Hellenides. It is suggested that all ophiolite belts in the Hellenides originated from a single source, and this was the Neotethyan Meliata/Maliac-Axios/Vardar ocean basin, parts of which obducted during the Mid–Late Jurassic on both continental margins, Apulian (containing Pelagonia) and European (containing units of the Serbo-Macedonian/Rhodope nappe stack), W-SW-ward and E-NE-ward, respectively. In this case, the ophiolite nappes should be considered far-traveled nappes on the continental parts of the Hellenides associated with the deposition of Middle–Late Jurassic ophiolitic mélanges in basins at the front of the adjacent ophiolite thrust sheets. The upper limit of the ophiolite emplacement are the Mid–Upper Jurassic time(Callovian–Oxfordian), as shown by the deposition of the Kimmeridgian–Tithonian Upper Jurassic sedimentary carbonate series on the top of the obducted ophiolite nappes. The lowermost Rhodope Pangaion unit is regarded as a continuation of the marginal part of the Apulian Plate (External Hellenides) which was underthrust during the Paleocene–Eocene time below the unified Sidironero–Kerdylia unit and the Pelagonian nappe, following the Paleocene–Eocene subduction and closure of a small ocean basin in the west of Pelagonia (the Pindos–Cyclades ocean basin). It preceded the Late Cretaceous subduction of the Axios/Vardar ocean remnants below the European continental margin and the final closure of the Axios/Vardar ocean during the Paleocene–Eocene time, which was associated with the overthrusting of the European origins Vertiskos–Kimi nappe on the Sidironero–Kerdylia nappe and, subsequently, the final collision of the European margin and the Pelagonian fragment. Subsequently, during a synorogenic Oligocene–Miocene extension associated with compression and new subduction processes at the more external orogenic parts, the Olympos–Ossa widow and the Cyclades, together with the lower-most Rhodope Pangaion unit, were exhumed as metamorphic core complexes. [ABSTRACT FROM AUTHOR]

The link between subduction and continental exhumation is explored using high‐resolution thermal histories from southern Great Xing'an Range (GXR), NE Asia and integrated with a regional low‐temperature thermochronology data synthesis from the NE Asian continental margin. The GXR thermal histories are constrained by multiple thermo‐, geochronometers (zircon, titanite, apatite U‐Pb, zircon, apatite (U‐Th)/He and apatite fission track). These data yield a large range in U‐Pb ages (292–119 Ma) with enhanced exhumation mainly during the early Cretaceous (ca. 155–110 Ma) in an extensional regime linked to roll‐back of the Paleo‐Pacific Ocean and consequent lithospheric thinning and delamination. Integrated with Cretaceous‐Cenozoic low‐temperature thermochronological data from the NE Asian continent margin, three regional phases of exhumation are recognized, which can be linked to changes in the geometry and kinematics of the subduction systems of the Paleo‐Pacific and Pacific oceans, demonstrating coupling between the subducting plate and the continental margin at active plate boundaries. Plain Language Summary: Thermochronological data sets enable orogen‐scale investigations into the spatio‐temporal patterns of exhumation on continental margins, and provide additional constraints on how the tectonic evolution of the crust is controlled by subduction. We employ geochronology (zircon U‐Pb), low‐temperature thermochronology (zircon, apatite (U‐Th)/He) and medium‐high temperature thermochronology (titanite, apatite U‐Pb) data to model the thermal evolution histories of the southernmost segment of the GXR in NE China. The inverse modeling results show rapid cooling and exhumation from ca. 155–110 Ma. This coincides with the initiation of slab roll‐back of the Paleo‐Pacific Ocean in NE Asia, which was responsible for cooling and exhumation in an extensional regime. In addition, we compile the available low‐temperature thermochronology data (zircon, apatite fission track and (U‐Th)/He) from the NE Asian continental margin from Late Cretaceous (ca. 110 Ma) to constrain regional exhumation events. These data show three main exhumation phases from the Late Cretaceous onwards. Combined with the data on the regional evolution of magmatism, sedimentary basins and deformation, the three exhumation phases can be linked to changes in the geometry of the Paleo‐Pacific ocean and Pacific ocean plates in NE Asia, thus showing coupling between continental exhumation and subduction. Key Points: The southernmost Great Xing'an Range experienced rapid cooling and exhumation during Early Cretaceous accompanied by voluminous magmatismA synthesis of low‐temperature thermochronology data from NE Asia shows three pulses of Mesozoic to Cenozoic exhumationThree exhumation phases on the East Asia margin are linked to subduction of the Paleo‐Pacific Ocean/Pacific Ocean from the late Early Cretaceous [ABSTRACT FROM AUTHOR]

Tectonic setting of the Late Carboniferous Cameng Formation in the north of South Qiangtang terranes (SQT) remains controversial. Here, we report new geochemical results for clastic rocks from the Cameng Formation. Our results show that the Index of Compositional Variability (ICV) is greater than 1, indicating these sediments experienced limited recycling and were probably derived from acid to intermediate magmatic rocks. The extent of weathering, with the Index of CIA vary from 67 to 75 (mean = 71), ICV > 1 (mean = 1.25) and the Th/U ratios > 4, is moderate in the source area. These new findings show that the Cameng Formation was most likely deposited in an unstable environment (continental island arc or active continental margin). Combined with other evidence, we further infer that the Early Paleozoic rocks (206Pb/238U ages varying from 438 to 502 Ma) presently exposed in the South Qiangtang terrane are the potential source of the Late Carboniferous depositions in the northern SQT, and were most likely deposited in a forearc basin under the in situ suture model, that is, the southward subduction of the Longmu Co-Shuanghu Tethys Ocean beneath the SQT. [ABSTRACT FROM AUTHOR]

Modern ideas about the tectonics of the Eurasian continental margin are considered. Cratons, fold belts, platforms, and sedimentary basins are briefly characterized. A significant part of the Arctic continental margins is represented by folded structures of different ages. In the course of geological evolution, tectonic structures successively formed, modified and died off, on which the processes of rifting and ocean formation were superimposed. Multidirectional tectonic movements, both vertical and horizontal, which led to the formation of the contours of oceanic basins and the ridges separating them, also influenced the continental margin. The destruction of the continental crust of the outer part of the continental shelf resulted in the formation of graben-like and rift troughs. The history of the Arctic oceanic basin began with the opening of the straits that connected the once isolated basin, the waters of which were largely desalinated. The latest stage of development was characterized by processes in which the transgressions and regressions of the Arctic Basin, the development and degradation of terrestrial and underground glaciation, and other processes played a leading role. [ABSTRACT FROM AUTHOR]

The transition between non‐rifted continental lithosphere and oceanic lithosphere in rifted margins can display a wide range of characteristics, depending on the regional tectonic evolution. The velocity and duration of the rifting process as well as the geodynamic setting influence the properties and geometry of the margins, which are often grouped into two main categories: magma‐poor and magma‐rich. We show how different types of rifted margins can influence the dynamics of continental collision, focusing on the time and depth of slab break‐off after collision and the fate of margin material. We find that rifted margins have a noticeable impact on subduction dynamics, as we observe large variability in slab break‐off times and depths. In particular, the presence of a rifted margin can delay slab break‐off to up to 60 Myr after the onset of collision. Our results show that a large portion of the weak crust of magma‐poor margins is likely to detach from the subducting plate and accrete to the upper plate, while the dense and strong mafic and ultramafic component of magma‐rich margins causes most of the margin to subduct and be lost into the mantle, leaving only a small fraction of transitional and oceanic crust at the surface. Therefore, the volume of accreted material is much larger when the margin is magma‐poor than magma‐rich, which is consistent with geological observations that fossil magma‐poor rifted margins are preserved in many mountain ranges, whereas remnants of magma‐rich rifted margins are scarce. Plain Language Summary: The transition between continental and oceanic lithosphere at rifted margins in nature is not a sharp boundary, but it is gradual and often characterized by the presence of altered crust. Such margins can be either magma‐poor or magma‐rich, depending on the volume and timing of magmatism during extension; in nature, we can find traces of rifted margins in collisional mountain belts, with magma‐poor margins being more easily preserved than magma‐rich ones. The available models for continental collision, however, do not often consider the presence of such margins. We model continental collision with the presence of a magma‐poor or magma‐rich rifted margin, aiming to provide an explanation for these observations and to see how the margins can affect the subduction process. We find that the presence of a rifted margin can have a significant impact on the evolution of the subduction system, with slab break‐off being significantly delayed in all cases. In the models, we find that part of the margin is always transferred to the overriding plate, and our results show that magma‐poor margins are more likely to be recovered, matching the observations that magma‐poor margins are more easily preserved than magma‐rich. Key Points: The presence of rifted margins in numerical models of continental collision can significantly delay slab break‐offThe type of margin (magma‐poor vs. magma‐rich) controls the dynamic of collision and the likelihood for the margin to be preservedThe volume of preserved margin material is much higher when to subduct is a magma‐poor margin than a magma‐rich one [ABSTRACT FROM AUTHOR]

Through detailed drill-core description, petrography, cathodoluminescence imaging, and geochemistry analysis, sedimentary deposits with a high content of volcanogenic components (27.6%) were discovered in the Shanxi Formation of the Daniudi Gas Field, Ordos Basin. The volcanogenic components include volcanogenic quartz, lava fragments (dominated by rhyolite fragments), tuff fragments, and tuffaceous matrix. In addition, at least two volcanic ash layers were discovered. Although the metamorphic rocks of the Precambrian succession in the ancient land of Yin Mountain are usually considered the primary source of the Shanxi formation, it is most likely that the volcanogenic components were derived from intermediate-acid volcanic materials that accumulated in the Daqingshan area during the Late Carboniferous to Early Permian. Those volcanogenic components are mainly transported by flowing water rather than by air from origin to basin. In addition, the accumulation of volcanic materials in the Daqingshan area was controlled by volcanic eruptions occurring solely in this area, rather than by the Inner Mongolia Orogenic Belt. Those volcanic eruptions were related to the southward subduction of the Paleo-Asian Ocean Plate beneath the northern margin of the North China Plate in the Late Carboniferous to Early Permian. The active continental margin related to the subduction of the Paleo-Asian Ocean Plate lasted at least until the Early Permian, and the closure of the Paleo-Asian Ocean must have occurred later than the Early Permian. [ABSTRACT FROM AUTHOR]

The China Central Orogenic System (CCOS), extending in an east-west direction in the middle part of China, is composed of the Early Paleozoic Altyn-North Qilian-North Qaidam-East Kunlun-North Qinling-North Tongbai orogens in the west and the Late Paleozoic to Early Mesozoic South Tongbai-Hong'an-Dabie-Sulu orogens in the east. They were produced by oceanic subduction and continental subduction/collision during the closure of the Proto-Tethys and the Paleo-Tethys oceans, respectively. Different types of metamorphic rocks with various ages are extensively exposed in these orogens, and they were produced at different geothermal gradients in different stages during the tectonic evolution of convergent continental margins, making them ideal targets to reconstruct the spatiotemporal evolution of the Eastern Tethys tectonic domain. In this article, an integrated study of metamorphic temperature (T)-pressure (P)-time (t) records is presented for metamorphic rocks along the CCOS, aiming to ascertain the change of metamorphic T/P ratios in both time and space, and then shed light on the tectonic evolution of the East Tethys tectonic domain in association with the thermal state change of convergent continental margins. The results indicate that despite the difference in metamorphic ages, metamorphic rocks in different orogens show a common trend with clockwise P-T-t paths. With respect to plate convergence for subduction and collision, regional metamorphism is categorized into three stages: (1) an early convergent stage, corresponding to low T/P Alpine-type blueschist- to eclogite-facies high-P to ultrahigh-P metamorphism; (2) a later convergent stage, corresponding to the medium T/P Barrovian-type medium-P amphibolite to high-P granulite-facies metamorphism; and (3) a post-convergent stage, corresponding to the high T/P Buchan-type low-P amphibolite to MP granulite-facies metamorphism. Nonetheless, a few metamorphic rocks only record a two-sage metamorphic evolution, with an early Barrovian-type high-P granulite-facies metamorphism and a late Buchan-type low-P granulite-facies metamorphic overprinting. In modern convergent plate margins, Alpine-type metamorphism mainly occurs in the stages of oceanic subduction and continental collision, Barrovian-type metamorphism takes pace in both stages of crustal thickening during continental hard collision and slab exhumation when continental subduction zones have evolved from compressional to extensional regimes, and Buchan-type metamorphism occurs in intracontinental rifting stage after the plate convergence. Therefore, the tectonic evolution of convergent continental margins can be reconstructed by combining metamorphic T/P ratios with their corresponding metamorphic facies series and metamorphic timing of metamorphic rocks. Based on the reported metamorphic rocks of different types and ages along the CCOS, it appears that the continental subduction/collision occurred at 500–490 Ma in the Altyn-North Qinling-North Tongbai orogens but 450–430 Ma in the North Qaidam-East Kunlun orogens, and the intracontinental rifting occurred at 460–450 Ma in the Altyn-North Qinling-North Tongbai orogens but 410–400 Ma in the North Qaidam-East Kunlun orogens, respectively, in the western Proto-Tethys domain. For the eastern Paleo-Tethys domain, in contrast, the continental subduction/collision occurred at 250–220 Ma and post-collisional intracontinental rifting occurred at 140–120 Ma. Furthermore, metamorphic evolution from low T/P ratios in the subduction/collision stage to high T/P ratios in the intracontinental rifting stage needs 40–60 Myr in the Proto-Tethys domain but about 110 Myr in the Paleo-Tethys domain. For the two different orogenic domains, therefore, the convergent continental margins underwent a common tectonic evolution from warm collision/cold subduction to hot rifting, which starts from continental subduction/collision characterized by the formation of medium-P amphibolite to high-P granulite facies series or high-P to ultrahigh-P eclogite facies series in compressional regimes, through exhumation of the deeply subducted crustal rocks, and terminates with intracontinental rifting featured by high-T to ultrahigh-T granulite facies series in extensional regimes. [ABSTRACT FROM AUTHOR]

The Bureya Massif is an important massif in the eastern Central Asian Orogenic Belt (CAOB), and contains voluminous late Palaeozoic–early Mesozoic granitoids that are ideal for investigating the tectonic evolution of the eastern CAOB. Here we report whole-rock geochemical, and zircon U–Pb geochronological and Lu–Hf isotope data for several granite intrusions in the northwestern Bureya Massif, with the aim of constraining the timing of magmatism and late Palaeozoic–early Mesozoic tectonism in the eastern CAOB. The zircon U–Pb dating results indicate that granitoids with ages of 306 ± 4, 243 ± 3, 191 ± 2, and 189 ± 4 Ma occur in the Bureya Massif. These, and previously published data, reveal that at least four stages of magmatism occurred in the northwestern part of the massif: ~306 Ma, ~243 Ma, 219–212 Ma, and ~201-189 Ma. The late Carboniferous (306 ± 4 Ma) gneissic monzogranites have an S and A-type granite affinity, and were derived with significant contribution of the mantle component in a syn- to post-collisional setting between the Bureya and Xing'an massifs. The Middle Triassic (243 ± 3 Ma) porphyritic I-type monzogranites, Early Jurassic (191 ± 2 Ma) porphyritic S-type syenogranites, and Early Jurassic (189 ± 4 Ma) gneissic S-type monzogranites have a supra-subduction zone geochemical signature. These granitoids formed in an active continental margin setting associated with southward subduction of the Mongol–Okhotsk oceanic plate. [ABSTRACT FROM AUTHOR]

The “Rinkian belt” of West Greenland is a metamorphic terrain of Paleoproterozoic age comprising: (1) the north Rinkian fold-thrust belt (FTB)—a pro- or fore-arc domain, highly deformed and metamorphosed with widespread anatexis; (2) the Prøven Igneous Complex—a magmatic arc characterized by hypersthene granitic rocks (“charnockites”); (3) the south Rinkian FTB—an inverted back-arc basin; and 4) a continental margin or foreland. Recognition of this tectonic architecture demonstrates that the “Rinkian” is a bona fide orogenic belt—the Rinkian orogen—and not simply the imbricated lower plate of the Nagssugtoqidian orogen. Arc plutons of the Prøven Igneous Complex were emplaced into the Karrat Group at ca. 1.90–1.85 Ga, dividing a back-arc basin into pro- and retro-arc domains. In the former—the north Rinkian FTB—WSWdirected thrusting (deformation events D1-D2) and high-grade metamorphism were taking place by ca. 1.875 Ga and were continuous through ca. 1.850 Ga with a peak temperature at ca. 1.830 Ma accompanied by anatexis in the Karrat Group and lower units of the Prøven Igneous Complex. In the retro-arc domain—the south Rinkian FTB—thrusting to the E (D1) began at ca. 1.870 Ma followed by thrusting to the W (D2) at ca. 1.830–1.820 Ga with displacement focused into a major high-temperature ductile shear zone which carried the Prøven Igneous Complex in the hanging wall of an Andean-type, crustal-scale, “pop-up” structure. High-temperature deformation continued during D3 when the pro-arc, arc, and retro-arc domains were shortened by bivergent detachment folding and thrusting at ca. 1.820–1.810 Ga. [ABSTRACT FROM AUTHOR]

The age of sedimentation (530–520 Ma) of the Teregtig Formation of South Tuva is estimated on the basis of U–Pb dating of detrital zircon grains from terrigenous rocks and Sr chemostratigraphy of carbonate rocks. It is shown that granitoids with an age of 580 Ma were the main source of detrital zircon. The presence of a representative Precambrian detrital zircon population indicates the deposition of sediments of the Teregtig Formation within the continental crustal block with a long evolution. During the accumulation of coarse-grained rocks of the Teregtig Formation, this part of the eroded area also comprised rocks of the Agardag ophiolite massif, which is evident from numerous angular clasts of olivine, pyroxenes, and Cr-spinels in the conglomerate matrix. [ABSTRACT FROM AUTHOR]

The Circum-Rhodope belt is a major tectonic unit in the Alpine orogen of northern Aegean region, which consists of metasedimentary rocks and unmetamorphosed arc-related Jurassic Evros ophiolite. Here, we review the biostratigraphic and detrital zircon ages available for the distinct units of the eastern Circum-Rhodope belt in Bulgaria and Greece. Both, biostratigraphic and radiometric ages consistently reveal a Middle Triassic to latest Late Jurassic timing of the sedimentation. Most importantly, the continuous depositional record sketches sedimentary sources from the continental margin (Rhodope) and the Jurassic arc system (Evros ophiolite) as documented mostly by the detrital zircons in clastic successions. [ABSTRACT FROM AUTHOR]

The NE-SW trending Jahazpur Belt in NW India has been considered correlative with the Aravalli Fold Belt, based on lithological similarities and greenschist facies metamorphic assemblages. The 2.54 Ga 'Jahazpur Granite' constitutes the basement for the overlying Hindoli and Jahazpur Group sediments in this belt. These meta sedimentary sequences presently occur as a greenschist facies ensemble of phyllite, marble, greywacke, and meta-conglomerate. In this study, the trace and Rare Earth Elements geochemistry of the Paleoproterozoic Hindoli Group metapelites and metagreywackes was evaluated for source characterization and tectonic setting. The transition metals and Th, La abundances, and Th/Sc, Zr/Sc and La/Sc ratios (1.19 and 1.5, 21.31 and 17.35 and 4.02 and 2.97, for metapelites and metagreywackes, respectively) of Hindoli Group suggest a felsic source for them and some degree of sediment maturity. Both Hindoli metapelites and metagreywackes are enriched in LREE and display significant negative Eu anomalies, further substantiating a predominant felsic component in the source region. The provenance modeling calculations indicate that the detritus was mainly sourced from Mangalwar Complex, along with some inputs from Jahazpur Granite, Bundelkhand TTG and Hindoli volcanics. Geochemical characteristics also discriminate a continental collision associated with an Active Continental Margin tectonic setting for the deposition of Hindoli sediments. [ABSTRACT FROM AUTHOR]

The United Arab Emirates (UAE)-Oman mountain belt exposes a large intact ophiolite thrust sheet that was obducted onto a rifted continental margin during the Late Cretaceous. Crustal properties of the mountain belt and the foreland region are important to better understand the mechanism of crustal deformation during the obduction process. In this study, we analysed P -wave receiver functions across the UAE and northern Oman mountain belt to determine the Moho depths, crustal properties and velocity structure beneath 53 broad-band seismic stations. Crustal thickness varies from 30.0 km in the western UAE to 46.6 km in the UAE-Oman mountain belt. The deeper Moho depth beneath the UAE-Oman mountain belt is the outcome of crustal thickening and flexure of the lithosphere during the obduction process. The eastern flank of the UAE-Oman mountain belt has relatively high- Vp / Vs ratios of 1.76–1.89. On the contrary, comparatively low- Vp/Vs ratios (1.61–1.67) are estimated in the western flank. Moreover, relatively low- Vp/Vs ratios (1.61–1.70) are observed in the foreland basin and western UAE. The high- Vp/Vs ratios and thick crust are indication of a thick ophiolite thrust sheet, while low- Vp/Vs ratios suggest that the crust is more felsic/intermediate in nature. The Vs -depth profiles in the mountain belt reveal a low- Vs zone beneath a remarkably high- Vs top layer. There is no such high- Vs top layer in the foreland area and western UAE. The high- Vs layer is correlated to a ∼10–15-km thick sequence of Semail crust and mantle ophiolite. Common Conversion Point imaging across the UAE-Oman mountain belt imaged the Moho boundary, which agrees with H-k stacking results, and intra-crustal discontinuities. [ABSTRACT FROM AUTHOR]

The Xinghongpu Formation is very important for understanding the Devonian tectonic evolution of the South Qinling orogenic belt. Geochemical, detrital zircon U-Pb-Hf isotopic studies were carried out on the Late Devonian metasedimentary rocks of the Xinghongpu Formation to constrain the depositional age, the provenance, and the tectonic setting. The detrital zircon U-Pb dating results revealed that the depositional age of the Xinghongpu Formation of the Late Devonian was not earlier than 363.2 Ma. The whole-rock geochemistry suggested that (1) this suite of metasedimentary rocks was mainly derived from quartzose sediments of mature continental provenance, with a small contribution from mafic and intermediate igneous provenance, and (2) the metasedimentary sandstone of the Xinghongpu Formation from the Late Devonian was deposited in an active continental margin to continental arc setting. The detailed detrital zircon U-Pb dating showed that the age spectra of detrital zircon could be divided into four groups: (1) 416–480 Ma, accounting for about 23%; (2) 740–850 Ma, accounting for about 19%; (3) 889–1017 Ma, accounting for about 19%; and (4) 1072–1146 Ma, accounting for about 12%. It also contained a group of Early Proterozoic zircons. The age and Hf isotope of the detrital zircons suggested that the clastic sediment deposited in the Xinghongpu Formation mainly came from the South Qinling Orogenic Belt and the North Qinling Orogenic Belt. The detrital zircon Lu-Hf isotopes indicated that most zircons were the products of the ancient crustal remelting, and the mantle-derived magmatic sources contributed to the provenance. The Xinghongpu Fm. formed in an oceanic basin in a continental margin environment with arc systems. [ABSTRACT FROM AUTHOR]

The development of trench-arc-backarc (TABA) systems is uniquely associated with modern-style plate tectonics on Earth. The Qilian orogenic belt in NW China records the evolution history of the Proto-Tethys Ocean at the transition time from the Proterozoic to Phanerozoic. This paper presents systematic studies of petrography, U–Pb chronology and geochemistry on various rocks from a middle-ocean ridge (MOR)-type ophiolite belt, active continental margin and back-arc basin in the Qilian orogenic belt to address the development of a modern-style TABA system. Arc magmas include felsic intrusions with ages of 531 to 477 Ma and felsic-mafic arc volcanic rocks with ages of 506 to 439 Ma, showing distinctive features of typical magmatic rocks formed at an Andean-type continental margin. The back-arc basin is recorded by a 490- to 448-Ma suprasubduction zone (SSZ)-type ophiolite with boninite, and Silurian turbidite flysch formation. We establish a three-stage tectonic history from the initiation of subduction to the formation of a mature Japan-Sea-type back-arc basin at the active continental margin in the Early Paleozoic era. (1) Northward subduction of Proto-Tethys Ocean initiated and the Andean-type continental arc developed at ~530 to 500 Ma with continual crustal thickening; (2) a tectonic transition occurred from an Andean-type active continental margin to a West Pacific-type active continental margin at ~500 to 490 Ma with rapid thinning of crust to ~35 km; and (3) mature ocean basins and back-arc-basin (BAB) ophiolites were formed in the back-arc extensional environment at ~490 to 450 Ma. [ABSTRACT FROM AUTHOR]

This paper focuses on one orogenic belt that formed during the Rinconada phase on the final stage of the Famatinian orogeny, between 445 and 410 Ma, which is well exposed at Sierra de Ramaditas and neighbouring ranges in western Argentina. The Ramaditas Complex is formed by metasedimentary and meta-ultrabasic rocks and amphibolites. This complex forms the upper nappe of a thrust stack resulting from westward thrusting. Deformation consists of an early high-temperature S1 foliation (stromatic migmatites), coeval with thrusting and metamorphism. Metamorphism attained peak P–T conditions of 6.0–6.9 kbar and 795–810 °C, at c. 440 Ma, i.e. coincident with the Rinconada orogenic phase. The lower unit and intermediate nappes crop out in the nearby sierras of Maz and Espinal and underwent low- to medium-grade Silurian metamorphism, respectively, together with the upper nappe, defining an inverted Barrovian-type metamorphism with T decreasing and P increasing downwards across the thrust stack (i.e. westward). We argue that the Rinconada orogenic phase developed near the continental margin of SW Gondwana, during a magmatic lull following accretion of the Precordillera terrane to the continental margin at c. 470 Ma. The active margin jumped to the west after accretion, and flat-slab subduction resumed in the early Silurian, provoking thrusting and imbrication of nappe stack under the still hot root (800–900 °C) of the older Famatinian magmatic arc. This 'hot-iron' process explains both the inverted Barrovian-type metamorphism and the missing overburden of 21 to 24 km implied by the P estimate. [ABSTRACT FROM AUTHOR]

Changes in sediment flux to continental margins are commonly interpreted in terms of tectonic growth of topography or climatic change. Here, we show that variations in sediment yield from orogenic systems, previously considered as resulting from climate change, drainage reorganisation or mantle processes can be explained by intrinsic mechanisms of mountain belt/foreland basin systems naturally evolving during post‐orogenic decay. Numerical modelling indicates an increase of sediment flux leaving the orogenic system synchronous with the cessation of deposition in the foreland basin and the transition from late syn‐ to post‐orogenesis. Experiments highlight the importance of lithospheric flexure that causes the post‐orogenic isostatic rebound of the foreland basin. Erosion of the rebounding foreland basin combined with continued sediment flux from the thrust wedge drives an acceleration in sediment outflux towards continental margins. Sediment budget records in natural settings such as the Northern Pyrenees or Western European Alps also indicate accelerated post‐orogenic sediment delivery to the Bay of Biscay and Rhône Delta respectively. These intrinsic processes that determine sediment yield to continental margins must be accounted for prior to consideration of additional external tectonic or climatic controls. [ABSTRACT FROM AUTHOR]

The closing time of the Paleo-Asian Ocean (PAO) has long been in the focus of research as well as of controversial debates. The Paleozoic A-type granites distributed in the Beishan Orogenic Belt (BOB) at the southern margin of the Central Asian Orogenic Belt (CAOB) provide pivotal clues to constrain the closure of the PAO. In this paper, the newly recognized Duhongshan A-type granites from the middle Huaniushan arc in the BOB (zircon LA-ICP-MS U-Pb ages of ca. 376–374 Ma) are thoroughly studied. The rocks have high SiO2, K2O contents with peralkaline character, and display high Zr + Nb + Ce + Y contents (354–543 ppm), 10,000 × Ga/Al (4.1–4.9), Y/Nb (3.2–5.3), Rb/Nb ratios (8.5–14.1), and a zircon saturation temperature in the range of 877–950 °C, indicative of A2-type granites affinities. The Duhongshan granites display enriched in Th and U; depleted in Ba, Sr, and Ti; with slightly positive whole-rock εNd(t) values (+1.86 to +2.21), indicating an origin related to partial melting of lower crustal material in post-collision extension settings. Combined with previous reported results, we conclude that the granitoids in the middle Huaniushan arc were mostly formed around 424–367 Ma and can be divided into two types based on petrochemistry: (a) A-type granites, which generally have high SiO2 and K2O, derived from the relatively shallow crustal source in post-collision tectonic settings; and (b) adakite and I-type granites, which display high Sr/Y ratios as well as Nb, Ta, and Ti depletion, likely generated from the melting of juvenile crust in active continental margin arcs. Integrating the previous regional investigations, we propose that the Hongliuhe–Niujuanzi–Xichangjing Ocean (HNXO) of the PAO was closed and transformed in the post-collision extensional tectonic stage during the Late Devonian and formed as post-collision magmatism, while the arc magmatism may be related to the subduction of the Liuyuan Ocean, which is located in the Southern HNXO. [ABSTRACT FROM AUTHOR]

The Longmaxi-1 black shales in the Upper Yangtze region are a vital source rocks in southern China. This study investigates the palaeoweathering conditions, provenance, and tectonic setting of the Longmaxi-1 black shale from an elemental geochemical perspective, ultimately revealing its tectonic setting. The results showed that the Longmaxi-1 black shales in the sedimentary period have the characteristics of primary deposition. The Longmaxi-1 black shales were deposited as a primary deposition under a mainly humid climate. However, fluctuations in climatic conditions were recorded from the bottom to the upper part of the formation. The parent rock of the Longmaxi-1 black shales in the Upper Yangtze region is a mixture provenance, mainly composed of intermediate-acid volcanic lithologies (granite and granodiorite), followed by mature quartzite and basalt. Black shale deposition is related to the tectonic setting of active continental margin and island arc-continent collision. The Cathayian orogenic belts and the North Qiangling orogenic belt may have played a role in the genesis of the Longmaxi-1 black shales within the Upper Yangtze region. This study provides significant clues regarding the reconstruction of the palaeoclimatic and palaeogeographical conditions of the Upper Yangtze region during the Early Silurian period. [ABSTRACT FROM AUTHOR]

The Triassic igneous complexes in the east flank of the East Kunlun orogenic belt (E-KOB) provide a window through which to investigate the Mesozoic magmatism in the E-KOB. Here, we report the precise timing of Triassic magmatism and magma petrogenesis of different rock types in the east flank of the E-KOB based on the petrology, mineral chemistry, geochemistry, zircon geochronology and Lu-Hf isotopes. Zircon U-Pb dating reveals that the Daheba complex was crystallized in 242–239 Ma. The rocks display enrichment in large-ion lithophile elements (LILEs) and LREEs and depletion in high field strength elements (HFSEs) and HREEs, which are typical of subduction-related magmatic rocks. The fine-grained granites (FGs) are characterized by a high SiO2 content (72.25–74.28 wt. %), a high differentiation index (DI = 95) and marked depletion in Sr, Ba and Eu, which indicates that the FGs are highly fractionated I-type granitoids. The zircon εHf(t) values from −3.6 to −1.1 with two-stage model ages (TDM2) of 1496–1340 Ma, which suggests that they were derived from an ancient Mesoproterozoic lower crust. The similarity in the REE patterns of the mafic microgranular enclaves (MMEs) and host granites (HGs) indicates that the mixing between mafic and felsic magmas could have contributed to the chemical variation of the MMEs. The mafic melts were derived from the partial melting of the mantle that had been metasomatized by slab-derived fluids. The MMEs show typical igneous textures, acicular apatites, sieve texture of plagioclase and reverse zoning of plagioclase, which correspond to magma mixing during petrogenesis. Our geochemical and isotopic data suggest that the Daheba complex formed in an active continental margin setting closely related to the northward subduction of the Palaeo-Tethys Ocean Plate beneath the E-KOB. [ABSTRACT FROM AUTHOR]

This contribution provides insights into ocean-floor hydrothermal metamorphism of the fast-evolving Dinaridic Neotethys. Mineralogical, geochemical and Sr isotope data collected from altered ophiolites and non-ophiolite basalts/andesites and tuffs of the active continental margin are consistent with hydrothermal alteration trajectories that reflect the host-rock composition. This suggests that hydrothermal fluxes were restricted within a simple closed seawater-fed system. Based on the initial isotopic ratios of Sr, two fluid–rock interaction trends are established: (a) low-to-medium degrees of metasomatism in pre-Middle Jurassic anorogenic ophiolites that progressively abated, and (b) increased intensities of metasomatism in post-Middle Jurassic orogenic ophiolites. This agrees with chlorite thermometry and Ca-Al-(Fe)-silicate phase chemistry. The metamorphic assemblages belong to the zeolite, prehnite-pumpellyite, prehnite-actinolite and greenschist facies. The facies is reliant on the temperature of hydrothermal systems and their fluid chemistry. Rare earth element (REE) phase geochemistry shows (a) variable fluid–rock ratios in chlorite and pumpellyite dependent on fluid temperatures, (b) prominent Eu and Ce anomalies that reflect the fluid oxidation state, (c) light REE/heavy REE mobilization attributed to prevalent ligand complexation, and (d) multi-phase fluid percolation across reaction zones of heterogeneous permeability. This study proposes initiation of simple hydrothermal system(s) at or near a spreading centre(s) in the infancy of the Dinaridic Neotethys. Such a system became more complex during Middle Jurassic and Early Cretaceous time with reactive hydrothermal fluids passing the recharge area and reaching the hot reaction zone. An abrupt obliteration of the established high-temperature regime ensued, following the final closure of the Neotethys. [ABSTRACT FROM AUTHOR]

The East Kunlun Orogenic Belt (EKOB) is the most important Triassic polymetallic metallogenic belt in China. A study about the petrogenesis of the ore-related intrusions is of great significance to the geodynamic evolution of orogenic belts. In this study, analysis of U–Pb zircon dating, whole-rock major and trace element compositions, and zircon Hf isotopes for the granitoids hosting the Aikengdelesite Mo (–Cu) and Halongxiuma Mo deposits in the EKOB are studied to determine their chronology and petrogenesis. Zircon date results show that the Aikengdelesite granite porphyry and the Halongxiuma granodiorite porphyry formed at 244.2 ± 1.7 Ma and 230.0 ± 1.0 Ma respectively. All samples of the Aikengdelesite granite porphyry and the Halongxiuma granodiorite porphyry which have high SiO2 and K2O contents, and low MgO and Cr, belong to the high-K calc-alkaline series. The Aikengdelesite granite porphyry samples show I-type geochemical affinities, whereas the Halongxiuma granodiorite porphyry samples are A-type granitoids. They all show negative zircon εHf(t) values (−7.4 to −3.3 and −3.7 to −2.5). We suggest that the Aikengdelesite granite porphyry may have been derived from the lower continental crust. While the Halongxiuma granodiorite porphyry could have formed by partial melting of basic lower crustal materials. By combining the results of this study with previous data, two magmatic and mineralization peak periods (278–237 Ma and 230–210 Ma) were observed in the Paleo-Tethys of the EKOB. Porphyry–skarn deposits occurring in the first episode were formed in the setting of an active continental margin related to the Paleo-Tethys Ocean plate subduction (e.g., Aikengdelesite porphyry deposit), while deposits occurring in the second episode were formed in a post-collisional setting (e.g., Halongxiuma porphyry deposit). [ABSTRACT FROM AUTHOR]

The Ailaoshan orogenic belt is one of the most significant orogenic belts in the southeastern margin of the Qinghai–Tibet Plateau. The widely developed magmatic rocks in this belt preserve the multi-stage tectonic evolution records of the South China Plate. As an important response to the Rodinia breakup tectonic event, the study of Neoproterozoic magmatic rocks in the area is of great significance for reconstructing the Neoproterozoic tectonic process of the Ailaoshan orogenic belt and the tectonic evolution of the South China Plate. Petrology, geochemistry, zircon U-Pb, and Lu-Hf isotopes of the Daping pluton in the Ailaoshan orogenic belt are studied in this paper. The Daping pluton is mainly divided into gabbros and granites. Gabbros and granites belong to the sub-alkaline series, which are relatively enriched in large ion lithophilic elements and depleted in high-field strength elements. The ΣREE contents of the gabbro are low with enrichment in LREEs and depletion in HREEs, and the degree of differentiation of light and heavy rare earth is low, with positive δEu and weak negative δCe anomalies. The ΣREE contents of the granite are low with enrichment in LREEs and depletion in HREEs, and the degree of light and heavy rare earth differentiation is high, with medium–weak negative δEu and weak positive δCe anomalies, suggesting an A2-type granite with A1-A2 transition characteristics. The weighted average age of the gabbro is 816.1 ± 4.1 Ma (MSWD = 0.11), with zircon εHf(t) values of −7.5–5.5. The magma source is a mixture of an ancient crust source and a new mantle source; the weighted average age of the syenogranite is 783.7 ± 8.1 Ma (MSWD = 1.4), with zircon εHf(t) values of −4.3–0.4. The magma source is mainly ancient crustal material (Ailaoshan Group), mixed with a small amount of mantle-derived material; the weighted average age of the monzogranite is 754.8 ± 6.1 Ma (MSWD = 3.0), with positive zircon εHf(t) values of 1.65–10.36. The magma source is a mixture of a large number of mantle-derived materials and a small number of crust-derived materials (Ailaoshan Group). The Daping pluton was formed in the transitional tectonic environment from post-collision to intraplate continental margin rift, corresponding to the Rodinia breakup process in the western margin of the South China Plate. [ABSTRACT FROM AUTHOR]

The Tarim Craton (or Tarim Block) is geographically located in the Northwest of China and tectonically between the Central Asian Orogenic Belt (CAOB) to the north and the Tethys to the south, which underwent a secular Precambrian evolution history from Ecoarchaean to Ediacaran. Owing to its marginal positions both in the Columbia (or Nuna) and Rodinia supercontinent configurations, it could play a key role in understanding the geodynamics of the assembly and break-up of the Precambrian supercontinents. This paper aims to present a critical review on the comprehensive synthesis of the Tarim Craton, detailing the Precambrian evolution processes and discussing its coupling with the Precambrian supercontinents. The Tarim Craton shows a typical plateform-like and double-layered structure, comprising the pre-middle Cryogenian basement with the middle Cryogenian-Ediacaran cover sequence. During its protracted basement evolution, diverse types and multiple stages of pre-Ediacaran intrusions were emplaced in the basement. Since Pleoproterozoic to early Cryogenian, crust reworking, rather than juvenile crust addition, played a key role in the final cratonization of its basement. Despite the final cratonization of the Tarim completed in the middle Cryogenian, both the bulk-rock Sm-Nd and zircon Lu-Hf isotope compositions demonstrated that its crust mainly formed in Archaean. Its characteristics of sedimentary features, metamorphic temporal-spatial architecture, the multiple phases and diverse types of intrusions reveal that the Tarim Craton is possibly composed of two main terranes with distinct features, i.e. the Northern Tarim Terrane (NTT) and the Southern Tarim Terrane (STT). It has been suggested that the STT could be a continental fragment that has drifted from West Africa, while the NTT shows a significant affinity with the India–North China Craton before Calymmian. Both were involved in the assembly and break-up of the Columbia supercontinent, and amalgamated during the assembly of the Rodinia. At the same time, it docked at the northern margin of Australia in the middle Cryogenian. Nevertheless, the subduction along the northern margin of the NTT continued at least until ca. 760 Ma. The voluminous 820–760 Ma diverse-type intrusions in the NTT have been ascribed to a genetic relation in the interaction between the circum-Rodinia subduction and the Rodinian superplume. The upwelling of the Rodinian superplume terminated the long-lasting subduction along the northern margin of the Tarim Craton. Since 740 Ma, being consistent with the break-up of the Rodinia, the Tarim Craton started drifting from the Rodinia supercontinent. The transition from signature to the passive continental margin of the middle Cryogenian-Ediacaran (for its cover sequences) rules out the possibility of the circum subduction along its northern margin lasting to early Palaeozoic. Additionally, with the Rodinia breaking up into the assembly of the Gondwana, the Tarim Craton, together with other continents in Eastern Asia, had docked at the margin of the Eastern Gondwana in early Palaeozoic. [ABSTRACT FROM AUTHOR]

Late Paleozoic tectonic evolution of northeastern China is complicated by the interaction of the Central Asian Orogenic belt development and the initiation of subduction from the Pacific Ocean plate along the eastern margin of Asia. In this study, we elucidate this problem by collecting new geochemical and geochronological data from late Paleozoic bimodal igneous rocks from the eastern margin of the Jiamusi block. By LA–ICP–MS zircon U–Pb dating, the 206Pb/238U age of the granitoid sample is 313–279 Ma, and the diabase 206Pb/238U age is 298–276 Ma. Rock geochemical studies show that diabase and granitoid have obvious chemical differentiation characteristics, indicating that they are the products of non-homologous magmatic evolution. Zircon Lu–Hf isotopes indicate that diabase magma originates from the metasomatism of the mantle wedge by subducting oceanic crust melts, granitoid magma mainly comes from the lower crust and the new crust. Our results together with a synthesis of existing data show that bimodal magmatism occurred in the study area from the Late Carboniferous to Early Permian when the Jiamusi block was an active continental margin and in a stretching background. Our synthesis of the existing data places our new data into a regional tectonic framework, and our proposed tectonic model provides the following new insights: (1) the northward expansion of the Paleo-Tethys Ocean from the Late Carboniferous to the Early Triassic led to the overall northward drift of the Paleo-Asian Ocean and the Xing'an-Mongolian Orogenic belt, which marks the easternmost segment of the Central Asian Orogenic belt, (2) the Paleo-Asian Ocean continued Late Permian–Early Triassic subduction caused back extension that rifted the Jiamusi and Songnen blocks apart and formed the Mudanjiang Ocean. [ABSTRACT FROM AUTHOR]

The tectonic properties of the Nanping‐Ninghua tectonic belt (NNTB) play a crucial role in understanding the tectonic evolution of the Wuyi orogenic belt, which is related to the Neoproterozoic‐Paleozoic tectonic evolution of the Cathaysian Block. In this study, We present comprehensive petrological, geochronological, and geochemical data on the metavolcanic rocks from the Louqian Formation in Changting, Fujian Province. Our results show that volcanism in Changting occurred between 740.4 and 723.5 Ma, based on zircon U–Pb data for the metavolcanic rocks. The metavolcanic rocks have SiO2 contents ranging from 68.22 to 71.56 wt %, high Al2O3 and Na2O + K2O contents (13.30–15.19 wt % and 7.56–8.25 wt %, respectively), and low CaO, MgO, and FeOT contents (0.09–1.25 wt %, 0.72–0.96 wt %, and 1.57–3.16 wt %, respectively). These samples are enriched in large‐ion lithophile elements (LILEs) such as Ba and Rb, and depleted in high‐field‐strength elements (HFSEs) including Nb, Ta, and Ti, with significant negative Eu anomalies, indicating an affinity for arc igneous rocks. Based on previous geological studies, we suggest that the NNTB formed in an active continental margin environment during the Nanhua Period. The subduction of oceanic crust led to the formation of the volcanic belt along the Nanping‐Ninghua continental margin, which was active until 696 Ma. During the Neoproterozoic, the North and South Wuyi terranes did not merge to form a single Wuyi terrane, and the Cathaysia Block was composed of several terranes. [ABSTRACT FROM AUTHOR]

The North Qaidam Orogenic Belt (NQOB) is characterized by widespread Palaeozoic magmatism and high to ultrahigh-pressure metamorphism that provides important information regarding the continental crust growth and tectonic evolution in the North Qaidam. Our work focuses on the geology, geochronology, whole-rock geochemistry, and Sr–Nd isotopy of granitoids in the Tanjianshan area in the northern NQOB. The results indicate that the 486–469 Ma adakitic and TTG-like granitoids originated from the partial melting of Middle–Late Mesoproterozoic lower crustal materials with the addition of juvenile mafic lower crust at high pressures under an active continental margin setting. The 396–392 Ma I-type granitoids originated from the partial melting of juvenile crustal materials with the addition of ancient crustal component in a post-collisional setting. Geochronological studies show that there are significant regional differences in magmatism between the northern and rest parts of the NQOB. In the northern part, extensive and prolonged magmatism was widespread during oceanic subduction (~526–460 Ma) and post-collisional extension (~420–350 Ma) but magmatism in the stage of orogenic collision was absent. The Early Palaeozoic adakitic magmatism suggest a significant continental crustal reworking in a subduction zone during 486–469 Ma along the NQOB. The initial oceanic subduction may have occurred prior to ca. 526 Ma. An intense and multiple-stage extension developed at ~420–350 Ma in the northern part of the NQOB following the orogenic collapse. Lithospheric delamination and subsequent mafic magma underplating may be the main geodynamic mechanism resulting in the uprooting of the continental crust and ore mineralization in response. [ABSTRACT FROM AUTHOR]

Orogens and volcanic arcs at continental plate margins are primary surface expressions of convergent plate tectonics. Although it is established that climate affects the shape, size, and architecture of orogens via orographic erosion gradients, the ascent of magma through the crust and location of volcanoes along magmatic arcs have been considered insensitive to erosion. However, available data reveal westward migration of late-Cenozoic volcanic activity in the Southern Andes and Cascade Range where orography drives an eastward migration of the topographic water divide by increased precipitation and erosion along west-facing slopes. Thermomechanical numerical modeling shows that orographic erosion and the associated leeward topographic migration may entail asymmetric crustal structures that drive the magma ascent toward the region of enhanced erosion. Despite the different tectonic histories of the Southern Andes and the Cascade Range, orographic erosion is a shared causal mechanism that can explain the late-Cenozoic westward migration of the volcanic front along both magmatic arcs. [ABSTRACT FROM AUTHOR]

Early Paleozoic black organic sediments and bentonites occur widely in the craton basin within the Yangtze block and are generally believed to be genetically related to a specific tectonic setting on the cratonic boundary. However, the intimate relationship between their origins and the dynamic mechanisms are unclear, as exemplified by the genesis of the black shale series and bentonites from the Wufeng Formation during the Ordovician–Silurian transition (OST). In order to reveal the relationship between the Wufeng Formation and the convergence of the Yangtze and Cathaysia blocks (i.e., the intracontinental Kwangsian Orogeny), two stratigraphic sections respectively in Zhaotong area (Northeast Yunnan) and Puyi area (Northwestern Guizhou) that were located in the semi‐restricted inner Yangtze Sea during the OST were systematically studied, on the basis of whole‐rock geochemical composition, pyrite δ34S (δ34Spy), total organic carbon (TOC), stable Sr isotope, pyrite framboid size distribution and zircon U‐Pb age, trace elements. The evidence shows that the paleo‐oceanic environment changed significantly at the turn of the early–late Katian and formed the black shale series in the Wufeng Formation. These acritarch assemblages were formed in the transition process of the Upper Yangtze Basin from passive continental margin basin to foreland basin during this interval. Based on previous research on the genetic relationship between black shale series and plate tectonic movement, a basin‐mountain evolution model suitable for South China in the Late Ordovician is presented. The two bentonites in the Wufeng Formation with U‐Pb ages of 445.5 ± 0.8 Ma and 441.9 ± 2.4 Ma primarily originated from the intermediate–acid volcanic eruption during the collision and convergence between the Yangtze and Cathaysia blocks in the Late Ordovician, the provenance region probably being located in the Jiangnan orogenic belt. Thus, we believe that the appearance of the black shale series and bentonite in the Wufeng Formation at the turn of the early–late Katian may represent the initiation of basin‐mountain transformation and the Kwangsian Orogeny in South China, which provides important evidence for the collision and convergence of the Yangtze and Cathaysia blocks in the Late Ordovician. [ABSTRACT FROM AUTHOR]

[Display omitted] • First geochronology, lithogeochemistry, and isotope data from a Tonian intraplate granite in the Southern Brasília Belt. • Whole-rock geochemistry and isotopic data indicate mixed mantle and crustal sources contributed to granite generation. • A-type granites suggest continental margin extension synchronous with the development of an outboard accretionary orogen. Late Tonian (ca. 735 Ma) A-type granite magmatism accompanied the development of a rifted continental margin in the southwestern portion of the São Francisco paleocontinent. Zircon U-Pb and trace elements, whole-rock lithogeochemistry, and Nd-Sr isotopes enable assessment of the tectonic setting. The Araras Granite shows high silica content (between 73 and 76 %) and ferroan character. The Y + Nb and Yb + Ta parameters vary respectively between 73 to 212 ppm, and 8.3 to 19.1 ppm, and the 1000*Ga/Al ratio varies between 2.6 and 3.4. Zircon U-Pb data indicates a crystallization age of 736 ± 12 Ma. The εNd (t) is slightly negative (between −3.6 and −1.7), and the depleted mantle model ages (T DM) range between 1.26 and 1.56 Ga. Binary mixing models based on whole-rock element and isotope geochemistry indicate that the granite was formed by mixing melts derived from two sources: a lithospheric mantle component and Paleoproterozoic magmatic arc rocks from the regional basement. The Araras Granite is concluded to represent a late stage of extension-related intraplate magmatism between ca. 840 and 730 Ma, associated with the evolution of a rifted continental margin in the southwestern São Francisco paleocontinent. Intraplate magmatism was partially synchronous with documented magmatic pulses within long-lived island arc systems that surrounded the paleocontinent. Extensional episodes in the rifted passive margin may be related to slab-pull forces driven by the outboard subduction dynamics. [ABSTRACT FROM AUTHOR]

• Subducted magma-poor rifted margins can efficiently exhume UHP rocks. • Conditions for magma-poor rifted margins may have arisen during Earth's middle age. • Abundant magma-rich margins in Early Earth prevented UHP rocks to exhume. In continental subduction, rifted margins can be carried to mantle depths (> 90 km) where ultra-high pressure (UHP) metamorphism above coesite stability is attained. Although different exhumation mechanisms for UHP rocks have been discussed, none of them integrate the recent understanding of rifted continental margins. Here, we perform high-resolution thermomechanical numerical experiments to demonstrate that segments of magma-poor rifted margins that reach UHP conditions can efficiently exhume back to shallower levels, while segments of magma-rich rifted margins cannot. This is because the thick layer of rocks with a basaltic composition in magma-rich margins becomes negatively buoyant during metamorphism, preventing their exhumation. This new concept might be pivotal for explaining why exhumed UHP rocks, a key feature of modern-style continental orogens, only appeared and became common late in Earth's history. We suggest that higher mantle potential temperatures and fertility in Earth's early history favored magma-rich rifted margins, making exhumation of UHP crust inefficient. Conditions for magma-poor rifted margins may have arisen during Earth's middle age (1.5–0.8 Ga) due to a colder, more refractory mantle that limited melting and magmatism. We argue that at the end of Neoproterozoic, these colder and positively buoyant magma-poor rifted margins were then subducted and efficiently exhumed to form the large collisional orogens of Gondwana where Earth's oldest coesite-bearing UHP rocks have been unequivocally found. Since then, UHP rocks have become a key and ubiquitous feature of continental orogens. [ABSTRACT FROM AUTHOR]

The Central Asian Orogenic Belt (CAOB) is one of the huge accretionary orogenic belts on the earth. NE China in the eastern segment of CAOB consists of several blocks connected by the accretionary belts and suture zones. The subduction and accretion of the Paleo-Asian Ocean (PAO) during the late Paleozoic around the Jiamusi Block and Zhangguangcailing Terrane (ZGCT) has been a subject of debate in terms of location, polarity, and timing. Our study found that the western margin of the ZGCT developed Early Carboniferous felsic magmatism with ages of 356–334 Ma newly obtained by LA–ICP–MS zircon U Pb dating. These igneous rocks, including strongly peraluminous rhyolites and I-type granites and rhyolites, display geochemical characteristics of medium- to high-K calc-alkaline series, and most of them have positive ε Hf (t) values, indicating an active continental margin setting. On the other hand, the Early Carboniferous magmatism was absent in the Jiamusi Block. Therefore, we suggest there existed a branch of the PAO that extended north-south along the western margin of the ZGCT. The magmatism in the western margin of the ZGCT migrated eastward to the western Jiamusi Block during the Carboniferous, accompanied by an increase in the depth of magma source, indicating an eastward advancing subduction of the PAO. The latest Carboniferous–earliest Permian marked a period of tectonic regime transition, during which the eastward-subducting plate along the western margin of the ZGCT began to roll back, resulting in the formation of bimodal volcanic rocks and A-type rhyolites across the ZGCT with a slight westward younging trend. Simultaneously, the eastern margin of the Jiamusi Block started to be controlled by the westward advancing subduction of the Panthalassa plate. • A newly found Early Carboniferous magmatic arc in western Zhangguangcailing Terrane. • There developed an eastward subduction along the western Zhangguangcailing • Terrane. • Zhangguangcailing Terrane was the western margin of Jiamusi Block in late Paleozoic. [ABSTRACT FROM AUTHOR]

The diamond-bearing Seve Nappe Complex (SNC) in the Scandinavian Caledonides records subduction of continental margin rocks to (ultra)high-pressure conditions at mantle depths, and exhumation thereafter from beneath the hinterland to the Earth's surface in the foreland. Structural data of the Upper, Middle, and Lower SNC in central Jämtland, Sweden demonstrate a triclinic bulk deformation during the exhumation of the still ductile SNC from crustal levels where migmatites formed. 40Ar/39Ar data from the Upper SNC constrain the timing of cooling through 450‒300 °C to be ~ 418 to 416 Ma. In combination with a review of the published pressure–temperature–time data and regional geology of the central Scandinavian Caledonides, four stages of exhumation of the central Jämtland SNC are summarized: (1) buoyancy-driven exhumation during ~ 455 to 433 Ma from ultrahigh-pressure depths to granulite-facies depths triggered by tectonic under-pressure; (2) tectonic exhumation in ~ 433 to 418 Ma at lower- to mid-crustal levels resulted from accretion of the Lower Köli Nappes onto Baltica; (3) eduction of the Western Gneiss Region lithosphere and piggyback transport of the SNC in ~ 418 to 375 Ma from hinterland to foreland, coupled with extensional faulting at mid- to upper-crustal levels; and (4) gravitational collapse- and erosion-driven exhumation following the end of the Scandian Orogeny at ~ 375 Ma. This multi-stage exhumation transported the SNC for > 100 km vertically from mantle depths to the Earth's surface and > 350 km horizontally from the Caledonian hinterland to the foreland. This contribution provides a typical example of the complex exhumation of deeply subducted continental rocks in orogenic belts. [ABSTRACT FROM AUTHOR]

Orogenic belts have been thought to form through plate convergence, involving subduction of oceanic lithosphere at continental margins (accretionary orogens), which may ultimately lead to ocean closure and continent-continent collision (collisional orogens). Intraplate orogens away from plate margins have been known, but the mechanisms controlling their evolution are poorly understood. The South China craton, including the Yangtze and Cathaysia blocks, underwent a Paleozoic orogenesis that formed a >500-km-wide orogenic belt with widespread granitoids that are unconformably overlain by Devonian cover sequences. The pre-Devonian basement rocks were subjected to strong deformation and greenschist-to amphibolite-facies metamorphism at 460-400 Ma. Paleozoic magmatism was characterized by voluminous crustally derived Silurian granitoids associated with incorporation of ancient crustal materials at 450-440 Ma and addition of juvenile mantle-derived melts at 420-410 Ma. Based on the absence of arc-like magmatism and the existence of ophiolites in the West Cathaysia terrane, geochemical evidence that oceanic crust existed beneath the East Cathaysia terrane, and geophysical evidence of contrasting lithospheres on both sides and two discrete slabs beneath their fault boundary, we propose that this Paleozoic orogenic belt was formed by collision between the two terranes that was driven by far-field forces during the assembly of Gondwana, and the East Cathaysia terrane represents oceanic lithosphere that was overthrusted by the continental crustal materials of the West Cathaysia terrane. Numerical modeling shows that this type of collision can explain the dynamics of the Paleozoic orogenesis in the South China craton and may be a mechanism for some orogens in which subduction-related igneous and metamorphic rocks are lacking. [ABSTRACT FROM AUTHOR]

The persistent debate over the timing of initial Arabia–Eurasia collision has eluded consensus for decades, with most estimates ranging widely from ~50 to 10 Ma along both the Anatolian and Zagros segments of the orogen. Here, we independently evaluate the timing and location of initial collision using a quantitative plate tectonic reconstruction that is the first to include the entire Arabian microcontinent and regions to the north in eastern Anatolia, northwestern Iran, and the Caucasus. The reconstruction combines new kinematic constraints from recent global plate models with a synthesis of available constraints on crustal shortening and continental and back-arc subduction to restore the pre-collisional geometries of the Arabian and Eurasian continental margins and to track their interaction through time. Our preferred model suggests that initial continental underthrusting, or soft collision, of the relatively thin Arabian passive margin with Eurasia occurred by ca. 42 Ma along the eastern Bitlis suture zone and began transmitting strain across central and eastern Anatolia, the Caucasus, and northwestern Iran. Collision inception then propagated westward into central Anatolia and southeastward into the northwestern Zagros Mountains by late Eocene time (ca. 40–35 Ma), the central Zagros by latest Eocene to early Oligocene time, (ca. 35–25 Ma), and finally the southeastern Zagros by latest Oligocene to middle Miocene time (ca. 25–15 Ma). The diachroneity of Arabia collision led to widespread upper-plate (Eurasian) contraction and a similarly time-transgressive magmatic lull that lagged behind the onset of collision by ~2–12 Myr. By incorporating the entire Arabian microcontinent and regions to the north, this new tectonic reconstruction highlights the diachronous nature of Arabia–Eurasia collision that occurred first along the Bitlis suture zone in eastern Anatolia during late middle Eocene time and became progressively younger to the southeast along strike of the Zagros suture zone. [ABSTRACT FROM AUTHOR]