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The response mechanism of the southeastern Tibet Plateau to the Indian-Eurasian collision is still controversial. The widely distributed shear systems in the Sanjiang area especially Ailaoshan-Red River shear system contribute a window to understand the tectonic evolution. Here we compile comprehensive geochronological data of the high-grade metamorphic rocks from the Ailaoshan-Red River shear system. The data reveal that the Ailaoshan metamorphic belt should be metamorphic complex with Middle-Late Triassic magmatic rocks and Cenozoic granites besides the Precambrian basement. The Cenozoic U-Pb age results of granitic rocks by accessory mineral within the Ailaoshan-Red River shear system range from ~41 Ma to ~20 Ma. The results of Ar-Ar dating of various minerals are in the range of ~40–5 Ma, concentrated in ~35–20 Ma. The U-Pb age results coincide basically with Ar-Ar data, indicating a rapid cooling process and reflecting a possible tectonic transition at ~20 Ma. The metamorphism and magmatism since the Cenozoic were not only unique to the Ailaoshan metamorphic belt, but also existed in the Chongshan and Gaoligongshan metamorphic belts. We infer that the Sanjiang area has a similar lateral extrusion deformation background and corresponds to the response of the India-Eurasia convergence process. [ABSTRACT FROM AUTHOR]

The India–Eurasia collision has produced a number of Cenozoic deep intracontinental basins, which bear important information for revealing the far‐afield responses to the remote collision. Despite their significance, their subsiding mechanism remains the subject of debate, with end‐member models attributing it to either orogenic or sedimentary load. In this study, we conduct flexural subsidence modeling with a two‐dimensional finite elastic plate model on the Hotan–Mazatagh section along the southern Tarim Basin, which defines a key region in the foreland of the West Kunlun Orogen, along the NW margin of the Tibetan Plateau. The modeling results indicate that the orogenic load of West Kunlun triggers the southern Tarim Basin to subside by up to less than ∼6 km, with its impact weakening towards the basin interiors until ∼230 km north from the Karakax fault. The sedimentary load, consisting of Cenozoic strata, forces the basin to subside by ∼2 to ∼7 km. In combination with the retreat of the proto‐Paratethys Sea and the paleogeographic reorganization of the Tarim Basin, we propose that surface processes, in particular a shift from an exorheic to an endorheic drainage system associated with the consequent thick sedimentary load, played a decisive role in forming deep intracontinental basins in the context of the India–Eurasia collision. [ABSTRACT FROM AUTHOR]

Sandstone-type uranium deposits (STUDs) are the most important global source of uranium. However, it is unclear why STUDs have a non-random distribution in time and space. It is generally thought that STUDs are formed by the circulation of groundwater in sandstone rocks. The groundwater is typically oxidized and sourced from local precipitation, which suggests the regional climate may have a role in the formation of STUDs. The groundwater circulation is mainly affected by basin evolution, which means that regional tectonism may also control the formation of STUDs. In this study, the author examined STUDs in Asia, and compiled previously reported ages for STUDs and compared these with the uplift history of the major ore-hosting regions and the late Mesozoic–Cenozoic climatic evolution of Asia. Apart from a few uranium deposits in the Transural region, most of the STUDs in Asia were formed during the Late Cretaceous to Quaternary, and can be classified into three stages: Late Cretaceous–early Paleogene (80–50 Ma; stage I), Oligocene–mid-Miocene (25–17 Ma; stage II), and late Miocene–present (8–0 Ma; stage III). The formation of STUDs in Asia was closely related to regional uplift caused by India–Eurasia collision, subduction of oceanic plates, and increased humidity during greenhouse climate periods and intensification of the Asian Monsoon. [ABSTRACT FROM AUTHOR]

Eocene igneous rocks along the Gangdese belt in southern Tibetan Plateau are important for understanding the India–Eurasia collision and Tibetan Plateau uplift. These magmatic rocks are widely considered to be related to roll-back or break-off of the Neotethyan slab during northward subduction. However, Eocene rhyolites in the northwestern Gangdese belt (SW Qiangtang margin) do not fit either the rollback or breakoff models. This paper investigates these Early Eocene lavas and compares them with contemporaneous igneous rocks along the Gangdese belt via detailed field observations, petrology, zircon geochronology, zircon Lu–Hf isotopes and whole-rock geochemistry. These felsic lavas form large outcrops in western Tibet and have two zircon U–Pb ages of 54.71 ± 0.14 Ma and 54.74 ± 0.27 Ma. They have high SiO2 and alkali contents, FeO*/MgO, and Ga/Al ratios as well as strongly negative Eu anomalies and slightly positive zircon εHf(t) values (+2.5 to +4.4). Both Ti-in-zircon and Zr saturation thermometers confirm high magmatic temperatures (~900°C). They are ferroan, A-type rhyolites. Furthermore, the distinctive low εHf(t) values imply that these rhyolites are likely partial melting products of the southwestern Qiangtang Terrane. The lithosphere in this region undergone long-term shortening and thickening since 80–95 Ma. Pre-thickened lithosphere may be a prerequisite for the Early Eocene delamination, and the simultaneous inducement is a far-field tectonic effect from the India–Eurasia collision. We suggest that: (1) India collided with Eurasia before 55 Ma and triggered delamination to form the Shiquanhe A-type rhyolites on the southwestern Qiangtang margin thereafter; and (2) tectonic stresses related to India–Eurasia collision during the Eocene were transmitted efficiently over large distances. [ABSTRACT FROM AUTHOR]

Volcanic arc degassing contributes significantly to atmospheric CO 2 levels and therefore has a pivotal impact on paleoclimate changes. The Neo-Tethyan decarbonation subduction is thought to have played a major role in Cenozoic climate changes, although there are still no quantifiable restrictions. Here we build past subduction scenarios using an improved seismic tomography reconstruction method and calculate the subducted slab flux in the India–Eurasia collision region. We find remarkable synchronicity between calculated slab flux and paleoclimate parameters in the Cenozoic, indicating a causal link between these processes. The closure of the Neo-Tethyan intra-oceanic subduction resulted in more carbon-rich sediments subducting along the Eurasia margin, as well as continental arc volcanoes, which further triggered global warming up to the Early Eocene Climatic Optimum. The abrupt termination of the Neo-Tethyan subduction due to the India–Eurasia collision could be the primary tectonic cause of the ∼50–40 Ma CO 2 drop. The gradual decrease in atmospheric CO 2 concentration after 40 Ma may be attributed to enhance continental weathering due to the growth of the Tibetan Plateau. Our results contribute to a better understanding of the dynamic implications of Neo-Tethyan Ocean evolution and may provide new constraints for future carbon cycle models. [ABSTRACT FROM AUTHOR]

Unravelling early Cenozoic basin development in northern Tibetan Plateau remains crucial to understanding continental deformation mechanisms and to assessing models of plateau growth. We target coarse‐grained red beds from the Cenozoic basal Lulehe Formation in the Qaidam basin by combining conglomerate clast compositions, paleocurrent determinations, sandstone petrography, heavy mineral analysis and detrital zircon U–Pb geochronology to characterize sediment provenance and the relationship between deformation and deposition. The red beds are dominated by matrix‐supported, poorly sorted clastic rocks, implying low compositional and textural maturity and short transport distances. Although most sandstones have high (meta)sedimentary lithic fragment contents and abundant heavy minerals of metamorphic origin (e.g., garnet, epidote and chlorite), spatiotemporal differences in detrital compositions are evident. Detrital zircon grains mainly have Phanerozoic ages (210–280 Ma and 390–480 Ma), but Proterozoic ages (750–1000 Ma, 1700–2000 Ma and 2300–2500 Ma) are also prominent in some samples. Analysed strata display dissimilar (including south‐, north‐ and west‐directed) paleocurrent orientations. These results demonstrate that the Cenozoic basal deposits were derived from localized, spatially diverse sources with small drainage networks. We advocate that initial sedimentary filling in the northern Qaidam basin was fed by parent‐rocks from the North Qaidam‐South Qilian belts and the pre‐Cenozoic basement within the Qaidam terrane interior, rather than southern distant Eastern Kunlun regions. Seismic and drilling well stratigraphic data indicate the presence of paleohighs and syn‐sedimentary reverse faults and noteworthy diversity in sediment thickness of the Lulehe Formation, revealing that the Qaidam terrane exhibited as several isolated depocenters, rather than a coherent basin, in the early stage of the Cenozoic deposition. We suggest the Cenozoic Qaidam basin to have developed in a contractional deformation regime, which supports models with synchronous deformation throughout most of Tibet shortly after the India‐Eurasia collision. [ABSTRACT FROM AUTHOR]

Carbonated eclogite has been identified as a significant component in the formation of intraplate alkaline basalts, typically attributed to stagnated subducted oceanic slabs, such as the Pacific plate beneath eastern China. However, it is unclear whether this component exists in other tectonic settings. Here, we present new zircon U Pb geochronology, mineral chemistry, and geochemical analyses of Cenozoic Tuoyun basanites and alkaline basalts from western Central Asia, where stagnated subducted oceanic slabs are absent, to elucidate the source properties and associated geodynamic processes. Olivine compositions (e.g., moderate Ni concentrations, low Mn/Fe and Ni/(Mg/Fe) ratios) and whole-rock chemistry (e.g., high Fe/Mn, Ca/Al, and Zr/Hf ratios, TiO 2 contents, and weak anomalies of Zr-Hf-Ti) suggest a carbonated eclogite in the mantle source of the Tuoyun basanites. Trace elements (positive Nb Ta anomalies and absence of positive Eu anomaly) and depleted to slightly enriched Sr-Nd-Hf isotopic compositions indicate that the basanites originated from mantle sources composed of variable proportions of altered oceanic crust (AOC) and carbonates. Synthesizing regional geochemical, geophysical studies and tectonic history, we propose that the continuous India-Eurasia collision triggered mantle upwelling, leading to the formation of a widespread carbonated eclogitic mantle source beneath western Central Asia. Our findings suggest that carbonate-rich mantle sources may also be present in areas without stagnated subduction slabs. • Widespread carbonated eclogitic components beneath western Central Asia. • Mantle upwelling induced by India-Eurasia collision. • Carbonate-bearing mantle source can exist in areas without stagnated subduction slabs. [ABSTRACT FROM AUTHOR]

It has long been debated whether the India-Eurasia collision was a single-stage event that began 60-55 million years ago, or whether it was a two-stage process that involved a collision between India and the Trans-Tethyan Arc before the early Paleocene, and the collision of India with Eurasia during the middle Eocene. Here, we report a late Paleogene angular unconformity (ca. 40-28 Ma) in western Myanmar. This angular unconformity developed around the same time as the Assam unconformity (NE India) but is younger than those found in northern Myanmar. Development of these unconformities indicates that an oblique convergence margin in western Myanmar formed before the middle Eocene, with a major dextral strike-slip fault (proto-Sagaing/Shan Scarp Fault) in the backarc. We interpret this oblique convergence margin to be partial continental collision between the West Myanmar Terrane (WMT) and NE India. In backarc regions, syn-rift successions of the Shwebo sub-basin have formed as a consequence of transtensional tectonics along the proto-Sagaing/Shan Scarp Fault since at least the late Paleocene. The syn-rift successions consist of Asian-derived materials that were not identified in the forearc because of the Wuntho-Popa Arc served as a geographical barrier. The presence of the unconformities and tectonic configuration of the Myanmar backarc sub-basins are inconsistent with the scenario inferred from paleomagnetic data, in which the WMT was part of an intra-oceanic arc at near-equatorial latitudes before the late Oligocene. Instead, we propose that the WMT has been part of continental SE Asia since at least the Paleocene (ca. 60-58 Ma). We reconsider the paleomagnetic data and suggest that the Mawgyi Arc, rather than the WMT, is the oceanic fragment that rifted from the northern Gondwana margin during the Late Jurassic. The Mawgyi Arc collided with continental SE Asia (WMT) during the Late Cretaceous, and then with India during the early Eocene (ca. 51-49 Ma). Our results support the collision between India and Eurasia is a multistage event. • Our findings support a two-stage India-Asia collision scenario. • The unconformities propagated from north to south over western Myanmar during the Paleogene. • Syn-Rift sequences of the Shwebo basin were produced by transtensional faulting. • The West Myanmar Terrane was anchored on SE Asia before the late Paleocene (60-58 Ma). [ABSTRACT FROM AUTHOR]

The onset of timing and the model of the India-Eurasia collision are strongly debated based on continental works, without systematic marine tectonic constraints. Two aseismic ridges, the Laccadives-Maldives-Chagos Ridge (LMCR) formed after the Deccan volcanism in western India and the Ninetyeast Ridge (NER) formed after the emplacement of the Rajmahal Traps in eastern India are prominent features in the Northeast Indian Ocean. The onset of a major and steady increase in magma production rates along the aseismic ridge associated with the significant slowdown of the northward moving Indian Plate is a likely indicator of the onset of the India-Eurasia collision. Using gravity-derived crustal thickness, we calculated the magma production rates along the LMCR and the NER, respectively. The steady increasing magma production rate along the LMCR and a southwestward jump of the Central Indian Ridge constrained the "soft" (India-island arc) and "hard" (India-Eurasia) collisions between western India and Eurasia to 50–52 Ma and ~41 Ma, respectively. The steady increasing magma production rate along the NER and the formation of the Mammerickx Microplate constrained the soft collision between eastern India and Eurasia to 47–49 Ma, and the extinction of the Wharton Ridge constrained the hard collision between eastern India and Eurasia to 38 Ma. Both the soft and hard collisions between western India and Eurasia are ~3 Myr earlier than the soft and hard collisions between eastern India and Eurasia, respectively. With systematic marine tectonic constraints, a two-stage eastward diachronous model of the India-Eurasia collision was proposed. [Display omitted] • Soft collision between western India and Eurasia was constrained to 50–52 Ma. • Soft collision between eastern India and Eurasia was constrained to 47–49 Ma. • Hard collision between western India and Eurasia was constrained to ~41 Ma. • Hard collision between eastern India and Eurasia was constrained to ~38 Ma. • A two-stage, eastward diachronous India-Eurasia collisional model was preferred. [ABSTRACT FROM AUTHOR]

Robust paleomagnetic results through geological time are one of the keys to understand the drift history of the eastern Qiangtang terrane (EQT). Here, we presented comprehensive petrographic observations and rock magnetic and paleomagnetic analyses of the early Carboniferous Upper Zaduo (ZD) limestone Formation (C1z2) from the Sulucun (SLC) section in the Zaduo area, EQT, to investigate its magnetic originality and geological significance. A total of 12 sites (131 samples) were collected. Photomicrograph observations indicate that the limestone samples were characterized by widespread carbonate veinlets. Electron microprobe and energy dispersive spectrometry analyses confirm that authigenic magnetite formed after pyrite. Rock magnetic analyses reveal the dominant magnetic minerals of pyrite and magnetite, with ‘wasp-waisted’ hysteresis loops and close to the “remagnetization trend” hysteresis parameters. Based on both thermal and alternating field demagnetizations, the characteristic remanent magnetization directions for most samples were isolated: Dg = 6.3°, Ig = 50.1°, kg = 54.9, α95 = 6.2° in-situ, and Ds = 330.2°, Is = 58.9°, ks = 5.9, and α95 = 20.5° after 2-step tilt correction. The κ (α95) value decreases (increases) after tilt-correction, and the ChRM directions failed both the McFadden (1990), Watson and Enkin (1993) fold tests, indicating post-folding magnetizations. The 11 site-mean directions yield a mean in-situ paleopole of 84.4°N, 200.3°E, and A95 = 6.8°, which is coincident with the post ∼53 Myr (especially around 40 Ma) paleopoles of the region. We therefore interpreted that these early Carboniferous limestone samples contain remagnetized magnetizations and that they were obtained after 53 Ma, most likely around 40 Ma, due to the far-field effect of the India–Eurasia collision.

Mesozoic and Cenozoic granites are widely distributed in the South Lhasa terrane of southern Tibet and record information about subduction of the Tethys oceanic plate and the India–Eurasia collision. This paper presents petrological, geochemical, zircon U–Pb and Hf isotopic characteristics of Cenozoic intrusive rocks in the Luocang area, South Lhasa terrane. Our data show these granites have ages of 54.4 ± 0.5 Ma and 47.2 ± 0.3 Ma (early Eocene), and are high-K, calc-alkaline, peraluminous, differentiated, I-type granites. The εHf(t) values of two samples are −9.59 to −4.15 and −7.85 to −5.36. These results suggest that the granites were derived from melting of the crust with no input of mantle source material. A review of data from Cenozoic granites of the South Lhasa terrane shows that they formed in a tectonic environment characterised by a gradual west-to-east transition to a post-collisional setting and are associated with breakoff of the Neo-Tethys oceanic plate. During the early Eocene continental collision, breakoff of the Neo-Tethys oceanic lithosphere caused the Indian plate to fold back resulting in a major asthenospheric disturbance. This was accompanied by an input of heat to the overlying continental crust, which caused melting of the mid to lower crust of the Lhasa terrane. The ascending magma underwent fractional crystallisation and was intruded to form the Eocene granites in the Luocang area. Two granitoids in the Luocang area of the South Lhasa terrane (southern Tibet) are high-K, calc-alkaline, peraluminous, differentiated, I-type granites and have negative εHf(t) values (−10 to −4). The U–Pb zircon ages of these two granitoids are 54.4 ± 0.5 Ma and 47.2 ± 0.3 Ma (early Eocene). The Luocang granites were formed by mantle heat input into the lower to middle crust of the Lhasa terrane; these crustal melts underwent fractional crystallisation during emplacement. [ABSTRACT FROM AUTHOR]

Influenced by the far‐field effect of the India–Eurasia collision during the Cenozoic, the Palaeozoic orogenic belt of the southern Tianshan mountains underwent tectonic activation. This resulted in the transmission of intense compressive deformation to the northern margin of the Tarim Basin, Kuqa Depression, where multiple east–west trending fold–thrust belts are formed. Exactly when the Cenozoic compressive deformation in the southern Tianshan orogenic belt was initiated is controversial. Growth strata are sediments of the syn‐tectonic events, and the age of the bottom boundary of the growth strata effectively constrains the initiation timing of the structural deformation. The Kuqa Depression currently receives sediments from the southern Tianshan mountains, and it is natural to use these Cenozoic strata to decipher the southern Tianshan's uplift history. Based on the detailed structural mapping and structural profile survey of the Kuqa Depression area, the Palaeogene Kumugelimu Formation growth strata in the Kuqa Depression were identified. Based on the magnetic stratigraphic sequence of the Cenozoic established by predecessors, the age of the bottom boundary of the Palaeogene Kumgelimu Formation is assumed to be 42–60.5 Ma. Combined with the analysis of the apatite fission‐track ages of the Mesozoic–Cenozoic clastic sediments in the Kuqa Depression by previous workers, there was an evident uplift and cooling event (~50 Ma) during the Palaeogene in the Kuqa Depression. The Cenozoic compression deformation in the south Tianshan and Kuqa Depression was then concluded to be initiated at approximately 50 Ma. [ABSTRACT FROM AUTHOR]

The mechanism of crustal deformation and the development of large offset strike‐slip faults during continental collision, such as the India‐Eurasia zone, remains poorly understood. Previous mechanical models were simplified which are either (quasi‐)2‐D approximations or made the a priori assumption that the rheology of the lithosphere was either purely viscous (distributed deformation) or purely localized. Here we present three‐dimensional visco‐elasto‐plastic thermo‐mechanical simulations, which can produce both distributed and highly localized deformation, to investigate crustal deformation during continental indentation. Our results show that large‐scale shear zones develop as a result of frictional plasticity, which have many similarities with observed shear zones. Yet localized deformation requires both a strong upper crust (>1022 Pa·s) and a moderately weak middle/lower crust (~1020 Pa·s) in Tibet. The brittle shear zones in our models develop low viscosity zones directly beneath them, consistent with geological observations of exhumed faults, and geophysical observations across active faults. Plain Language Summary: Large offset strike‐slip faults are one of the key surface features of continental collision, such as in Tibet. These narrow belts of strike‐slip faults accommodate strong deformation, and deciphering their mechanism of formation helps to understand the complex dynamics of India‐Eurasia collision. Yet previous models developed to address this either assumed simplified rheologies or employed low numerical resolutions that is insufficient to simulate the spontaneous formation of localized zones. Here, we present high‐resolution 3‐D visco‐elasto‐plastic thermo‐mechanical models that simulate the formation of large‐scale strike‐slip faults during Indian indentation, while also taking distributed deformation into account. Our simulations show that a combination of a strong upper crust and a moderately weak middle/lower crust produces faults that are, to first order, consistent with observed ones in the Tibet region. Localized deformation usually initiates at the brittle‐ductile transition, and a weak middle/lower crust facilitates subsequent shear localization such that the shear zones cut through the whole crust. The craton‐like strong terranes can sustain large stresses and initiate large offset faults along their boundaries. Key Points: 3D VEP high‐resolution thermomechanical models accounting for both localized and distributed deformation during India‐Eurasia collisionMajor strike‐slip faults develop preferentially in models with a strong upper and a moderately weak lower crustLower crustal flow and strong terranes surrounding Tibet facilitate fault formation [ABSTRACT FROM AUTHOR]

The offset of geological bodies provides robust evidence of displacement along a fault or ductile shear zone. The amount of displacement along the Xuelongshan–Diancangshan–Ailaoshan structural system, southeastern Tibetan Plateau, is uncertain because of the lack of offset geological markers. This NNW–SSE‐trending system is developed in three isolated metamorphic complexes and interjacent nonmetamorphosed rocks. They are expected to record similar post‐Eocene strain, although their structural patterns should be distinct. Geological mapping in the area between the Xuelongshan and Diancangshan metamorphic complexes has revealed a small Eocene basin, the Madeng Basin, located to the west of the structural system. The sedimentary and volcanic successions of the Madeng Basin are comparable to those of the Jianchuan Basin, which is located to the east of the structural system. Zircon U–Pb geochronological and bulk geochemical data demonstrate that the volcanic rocks of both basins formed during 37–34 Ma and share the same geochemical features. These data suggest that the Madeng and Jianchuan basins previously constituted a single basin, with the distribution of high‐K volcanic rocks in the basins defining an ENE–WSW‐trending volcanic belt that shows a limited dextral offset of ≤20 km across the Xuelongshan–Diancangshan–Ailaoshan structural system. Therefore, the northern segment of the structural system records no evidence of large‐scale lateral movement/displacement. The results suggest that the Indochina block, which is bounded by the Xuelongshan–Diancangshan–Ailaoshan structural system to the east and the Sagaing Fault to the west, has not extruded southward as a whole but rather has been deformed by pervasive crustal shortening. [ABSTRACT FROM AUTHOR]

Field observations, petrology, zircon geochronology, whole-rock geochemistry, and Sr-Nd isotopes were used to reveal the lithology, age, and tectonic setting of the protoliths of the Sangsang mafic schists in the Yarlung Zangbo Suture Zone (YZSZ), central southern Tibet. The mafic schists occur as exotic blocks within the accretionary complex of the YZSZ. Relic amygdaloidal features indicate the schist protoliths were volcanic rocks. The mineral assemblage mainly comprises riebeckite + magnesioriebeckite + chlorite + sericite + albite + relic clinopyroxene. The youngest group of zircon ages constrains the formation time of the protoliths to 149.2 ± 2.2 Ma (i.e., latest Jurassic). Abundant Paleozoic and older zircons suggest the protolith volcanic rocks were erupted onto a continental terrane. Whole-rock geochemical and Sr-Nd isotopic data indicate the protoliths were of ocean island basalt affinity. The mafic schists mostly have high-Ti, alkaline, basaltic compositions with 43.57–46.93 wt% SiO 2 , 3.27–7.24 wt% Na 2 O + K 2 O, and 4.04–4.69 wt% TiO 2. The schists are enriched in light rare earth elements relative to heavy rare earth elements, and have (La/Yb) N = 5.85–8.53 and small positive Ta and negative Zr-Hf anomalies. (87Sr/86Sr) i values vary from 0.7044 to 0.7055, while (143Nd/144Nd) i ranges from 0.512670 to 0.512727, with εNd(t) values of +4.4 to +5.5. The protoliths of the mafic schists were probably formed in a within-plate extension setting associated with mantle plume upwelling and melting of continental lithosphere. This setting was related to the Late Jurassic continental breakup of Argoland off the northern margin of east Gondwana, and thus marked the paleoposition of the northern edge of Greater India before the breakup of India from east Gondwana during Early Cretaceous. The N-S extent of Greater India at that time was ~2400 km. This further indicates how the India–Eurasia continental convergence has been accommodated. Unlabelled Image • Sangsang mafic schists in southern Tibet are metamorphosed OIB-type rocks. • The protoliths formed during latest Jurassic continental breakup of east Gondwana. • The N S extent of Greater India is defined to be ~2400 km. [ABSTRACT FROM AUTHOR]

The Dras Arc in NW India Himalaya is a belt of basaltic‐andesites intercalated with arkose‐dominated volcaniclastic rocks of the Nindam Formation situated along the Indus Suture between India and Eurasia. Debates exist as to whether these rocks developed in a forearc basin to the Eurasian margin or as part of an intraoceanic island arc system that collided with either India or Eurasia before final continental collision. Detrital zircons from the Nindam Formation yield U‐Pb age spectra with dominant youngest age populations of ~84–125 Ma, corresponding with arc magmatism. Sandstone provenance analysis from the Nindam Formation indicates that the Dras Arc evolved from an undissected arc to dissected arc over a period of ~41 Myr. Slightly older, smaller populations occur at ~135–185 Ma, corresponding with reported ages of Neotethyan ophiolites (e.g., Spongtang). The basal section of the Nindam Formation reveals the presence of arc‐derived basaltic‐andesite and tonalite clasts, plus ophiolitic components sourced from an adjacent accretionary complex. There is a distinct absence of quartz or felsic granitic clasts, suggesting that the Nindam Formation did not develop as a forearc basin to the Ladakh Batholith of southern Eurasia but rather as separate intraoceanic island arc. A distinct "Gondwanan" signature occurs in all samples, with zircon age peaks at ~514–988, ~1000–1588, ~1627–2444, and ~2500 Ma. We suggest that the Dras and Spong arcs are the same intraoceanic island arc system that developed as a result of subduction initiation along NNE‐SSW transform faults perpendicular to the Indian and Eurasia continents. Key Points: The Nindam Formation was deposited in an intraoceanic forearc basin as distal deposits, largely sourced from ~84–125 Ma Dras Arc rocksA distinct "Gondwanan" signature composed of Precambrian populations occurs in all samplesThe intraoceanic Dras Arc collided and accreted onto the passive margin of India before final continental collision [ABSTRACT FROM AUTHOR]

Abstract Topographic divides along the northeastern marginal zone of the Tibetan Plateau separate tributary drainage systems that flow into the Yellow River. Field investigations and topographic analysis indicate that: i) Late Quaternary–Holocene sedimentary sequences are deformed into a series of left-stepping WNW–ESE-trending en echelon flexural folds; ii) the folds form topographic divides that separate drainage systems that flow into the Yellow River; and iii) the regional axis of maximum compressive stress, as inferred from flexural folds and active fault-related structures, trends ENE–WSW, consistent with geophysical and seismic data. These results demonstrate that the topographic divides formed through active flexural folding and faulting in the northeastern marginal zone of the Tibetan Plateau, corresponding to the ongoing northeastward shortening of the plateau accommodating the Eurasia-India continental collision. Highlights • Topographic divides formed by active flexural folding in the NE margin zone of the Tibetan Plateau. • Topographic divides separate the tributary drainage systems of the Yellow River. • The late Quaternary–Holocene sedimentary sequences are deformed into a series of left-stepping flexural folds. • The regional axis of maximum compressive stress inferred from flexural folds is oriented to ENE–WSW. [ABSTRACT FROM AUTHOR]

The Cenozoic India-Eurasia collision is evidently recorded in the Qaidam Basin, which is located in the north margin of the Tibetan Plateau. The present study describes a dextrorotary phenomenon at the end of the Eocene in Lenghu Area in the northern Qaidam Basin, discovered in sedimentary and tectonic records. This phenomenon is interpreted to have been a result of the levorotatory movement along the Altyn Tagh Fault (ATF) based on the following evidence. First, provenance, as analyzed by heavy mineral assemblages, was slightly deflected from southwestward to the westward by about 45°. Second, paleocurrent inferred from dip logging and seismic reflection changed clockwise by approximately 25°. Third, there is evidence of increases in fault activity in the area, especially in northwest-southeast-trending branches relative to older west-east-trending branches. Increases in faulting coincide with abrupt increases in sediment supply in the Oligocene, after earlier decreases based on total sand content during the Eocene. Our results demonstrate that the northern margin of the Tibetan Plateau synchronously responded to the initiation and termination of the India-Eurasia collision. The levorotatory strike slip of the ATF was immediately triggered by the complete collision at the end of Eocene, and the strike-slip movement caused the dextrorotary phenomenon in the Lenghu Area. [ABSTRACT FROM AUTHOR]

Abstract The Spongtang Massif is a remnant of Neotethyan ocean crust emplaced onto the Indian passive margin along the Indus-Yarlung-Tsangpo Suture in the NW Himalayan region of Ladakh. The age, tectonic evolution and timing of ophiolite obduction are critical to our understanding of the mechanisms via which entire oceans are formed, consumed and partly preserved before the onset of terminal continent-continent collisions. Geochemistry of the gabbro and basaltic units suggest the presence of both MORB-type and primitive arc-related mafic rocks. Zircons extracted from the Spongtang Massif gabbros yield U-Pb (SHRIMP) ages of 136–133 Ma with initial ε Hf values of +14 to +16, indicating Early Cretaceous juvenile, depleted mantle sources devoid of contamination by older continental crust. Previously, Middle Jurassic (~177 Ma) zircon ages were obtained from gabbro and we suggest these represent MORB-type Neotethyan oceanic crust through which a younger intra-oceanic island-arc (Spong arc) developed in response to subduction initiation during the Early Cretaceous (~136 Ma). Our zircon ages are consistent with Early Cretaceous ages obtained for radiolarian cherts within the Spong Arc complex. Subduction beneath the Spong Arc continued until its collision with the northern Indian continental margin during the early Eocene. We suggest that the Spongtang Massif is equivalent to the nearby Dras island arc terrane. Intra-oceanic subduction beneath this system was possibly initiated along NNE-SSW trending transform faults in the Neotethyan Ocean, along which different ages of ocean crust was juxtaposed, thereby development of the Early Cretaceous Spong Arc is superimposed on the older Jurassic Spongtang N-MORB crust. The juvenile ɛ Hf signature indicates the subduction system that spawned the Spong island arc was not related to the coeval Trans-Himalayan (Ladakh-Gangdese) arc that developed along the southern margin of Eurasia. The age, composition and nature of geological relationships with the underlying Indian rocks indicate the Spong Arc was a juvenile, intra-oceanic terrane that first collided with India before the onset of final continent-continent collision. Therefore, final late Eocene Neotethys closure was between the Kohistan-Ladakh (Eurasian) continental arc and the already inactive Indian + Spongtang margin. Graphical abstract Unlabelled Image Highlights • Gabbros from Spongtang ophiolite yield U-Pb zircon (SHRIMP) Early Cretaceous age of ~136 Ma. • Initial ε Hf zircon values of +14 to +16 indicate juvenile source devoid of older continental crust. • Early Cretaceous Spong Arc superimposed on older Jurassic N-MORB crust. • Spongtang ophiolite-Spong arc first collided with India before final continental collision. [ABSTRACT FROM AUTHOR]

We used an updated data set of 192 GPS-derived surface velocities and 393 earthquake focal mechanisms (Mw > 3.0, hypocenter depths < 30 km) to evaluate the spatial variations in the surface strain rate and crustal stress regime throughout the Pamir Plateau and its surrounding regions. The strain rate field was estimated using the spline in tension approach that solves for the surface velocity in a rectangular grid and the stress field was predicted from focal mechanism solutions using the damped regional-scale stress inversion (DRSSI) method of Hardebeck and Michael (Journal of Geophysical Research, 10.1029/2005jb004144, 2006). The results show that the crustal stress field around the Pamir Plateau is predominantly characterized by NNW-SSE compression and E-W extension, which is consistent with the principal orientations of the two-dimensional surface strain rate tensor. This agreement supports the notion that the Pamir and southwestern Tien Shan are uniformly strained blocks. In particular, the fan-shaped rotational pattern between Shmax and the strain rate from the western Pamir to the Tajik Basin shows that the counterclockwise rotation of the Shmax orientation is associated with vertical deformation, which is consistent with the idea of Schurr et al. (Tectonics 33(8):2014TC003576, 2014) concerning the gravitational collapse and westward extrusion of the crust in the western Pamir. We propose that such a stress-strain pattern, dominated by NNW-ESE oriented compression and E-W trending extension, originated from a combination of the northward push of the Indian continent and the southward subduction of the Tien Shan. [ABSTRACT FROM AUTHOR]

The Lüliang Mountains, located at the western margin of the Trans-North China Orogen, are thought to have undergone several uplift events during the late Mesozoic and Cenozoic due to far field effects of the India–Eurasia collision and/or Pacific Plate subduction. However, the timing and mechanisms of late Cenozoic uplift of the Lüliang Mountains are not clear. Our investigation of the source characteristics of the Shilou red clay sequence, an eolian deposit on the eastern Chinese Loess Plateau adjacent to the Lüliang Mountains, provides a new understanding of the relationship between the material composition of the eolian sediment and regional tectonic activity. Grain size data for the Shilou red clay sequence reveal an abrupt increase at ca. 5.7 Ma, and U Pb detrital zircon geochronology indicates that the major source areas of Shilou red clay shifted after ca. 5.7 Ma, from the Junggar Basin, western Mu Us desert, and Gobi-Alxa arid lands, to the eastern Mu Us desert and the Lüliang Mountains. Detrital zircons younger than 5.7 Ma in the Shilou red clay have similar U and Th contents to zircons from the Lüliang Mountains, indicating that the mountains acted as a proto-source for the red clay after ca. 5.7 Ma. We suggest that the influx of coarser grained sediment is due to rapid uplift of the Lüliang Mountains at ca. 5.7 Ma, and that this timing is consistent with northeastward propagation of mountain uplift in response to the India–Eurasia collision. [ABSTRACT FROM AUTHOR]

The India-Eurasia collision zone is the largest deforming region on the planet; direct measurements of present-day deformation from Global Positioning System (GPS) have the potential to discriminate between competing models of continental tectonics. But the increasing spatial resolution and accuracy of observations have only led to increasingly complex realizations of competing models. Here we present the most complete, accurate, and up-to-date velocity field for India-Eurasia available, comprising 2576 velocities measured during 1991-2015. The core of our velocity field is from the Crustal Movement Observation Network of China-I/II: 27 continuous stations observed since 1999; 56 campaign stations observed annually during 1998-2007; 1000 campaign stations observed in 1999, 2001, 2004, and 2007; 260 continuous stations operating since late 2010; and 2000 campaign stations observed in 2009, 2011, 2013, and 2015. We process these data and combine the solutions in a consistent reference frame with stations from the Global Strain Rate Model compilation, then invert for continuous velocity and strain rate fields. We update geodetic slip rates for the major faults (some vary along strike), and find that those along the major Tibetan strike-slip faults are in good agreement with recent geological estimates. The velocity field shows several large undeforming areas, strain focused around some major faults, areas of diffuse strain, and dilation of the high plateau. We suggest that a new generation of dynamic models incorporating strength variations and strain-weakening mechanisms is required to explain the key observations. Seismic hazard in much of the region is elevated, not just near the major faults. [ABSTRACT FROM AUTHOR]

A volcanic-sedimentary succession of Paleogene age is exposed in isolated patches at the southern margin of the Tajik block in the Ghor province of Central Afghanistan. The volcanic rocks range from basalts and andesites to dacites, including adakites. They are intercalated with sedimentary rocks deposited in shallow marine environments, dated biostratigraphically as Paleocene-Eocene. This age corresponds to the age of the Asyābēd andesites located in the western Ghor province estimated by the 40 Ar/ 39 Ar method as 54 Ma. The magmatism post-dates the Cimmerian collision between the Tajik block (including the Band-e-Bayan block) and the Farah Rod block located to the south. While the investigated volcanic rocks apparently bear geochemical signatures typical to an active continental margin environment, it is presumed that the magmatism was related to rifting processes most likely initiated by far-field tectonics caused by the terminal collision of the Indian plate with Eurasia (Najman et al., 2017). This event led to the dextral movement of the Farah Rod block, particularly along Hari Rod (Herat) fault system, resulting in the development of a transtensional regime in the proximal southern margin of the Tajik block and giving rise to a rift basin where marine sediments were interbedded with pillow lavas intruded by sheeted dyke series. [ABSTRACT FROM AUTHOR]

The Late Cretaceous location of the Lhasa Terrane is important for constraining the onset of India-Eurasia collision. However, the Late Cretaceous paleolatitude of the Lhasa Terrane is controversial. A primary magnetic component was isolated between 580 °C and 695 °C from Upper Cretaceous Jingzhushan Formation red-beds in the Dingqing area, in the northeastern edge of the Lhasa Terrane, Tibetan Plateau. The tilt-corrected site-mean direction is D s / I s = 0.9°/24.3°, k = 46.8, α 95 = 5.6°, corresponding to a pole of Plat. / Plon. = 71.4°/273.1°, with A 95 = 5.2°. The anisotropy-based inclination shallowing test of Hodych and Buchan (1994) demonstrates that inclination bias is not present in the Jingzhushan Formation. The Cretaceous and Paleogene poles of the Lhasa Terrane were filtered strictly based on the inclination shallowing test of red-beds and potential remagnetization of volcanic rocks. The summarized poles show that the Lhasa Terrane was situated at a paleolatitude of 13.2° ± 8.6°N in the Early Cretaceous, 10.8° ± 6.7°N in the Late Cretaceous and 15.2° ± 5.0°N in the Paleogene (reference point: 29.0°N, 87.5°E). The Late Cretaceous paleolatitude of the Lhasa Terrane (10.8° ± 6.7°N) represented the southern margin of Eurasia prior to the collision of India-Eurasia. Comparisons with the Late Cretaceous to Paleogene poles of the Tethyan Himalaya, and the 60 Ma reference pole of East Asia indicate that the initial collision of India-Eurasia occurred at the paleolatitude of 10.8° ± 6.7°N, since 60.5 ± 1.5 Ma (reference point: 29.0°N, 87.5°E), and subsequently ~ 1300 ± 910 km post-collision latitudinal crustal convergence occurred across the Tibet. The vast majority of post-collision crustal convergence was accommodated by the Cenozoic folding and thrust faulting across south Eurasia. [ABSTRACT FROM AUTHOR]

The pattern and timing of collision between India and Eurasia have long been a major concern of the international community. However, no consensus has been reached hitherto. To explore and resolve the disagreements in the Himalayan study, in this paper we begin with the methodology and basic principles for the anatomy of composition and nature of convergent margins, then followed by an effort to conduct a similar anatomy for the India-Eurasia collision. One of the most common patterns of plate convergence involves a passive continental margin, an active continental margin and intra-oceanic basins together with accreted terranes in between. The ultimate configuration and location of the terminal suture zone are controlled by the basal surface of the accretionary wedge, which may show fairly complex morphology with Z-shape and fluctuant geometry. One plausible method to determine the terminal suture zone is to dissect the compositions and structures of active continental margins. It requires a focus on various tectonic elements belonging to the upper plate, such as accretionary wedges, high-pressure (HP)-ultra-high-pressure (UHP) metamorphic rocks, Barrovian-type metamorphic rocks and basement nappes, together with superimposed forearc basins. Such geological records can define the extreme limits and the intervening surface separating active margin from the passive one, thus offering a general sketch for the surface trace of the terminal suture zone often with a cryptic feature. Furthermore, the occurrence of the cryptic suture zone in depth may be constrained by geophysical data, which, in combination with outcrop studies of HP-UHP metamorphic rocks, enables us to outline the terminal suture zone. The southern part of the Himalayan orogen records complicated temporal and spatial features, which are hard to be fully explained by the classic 'two-plate-one-ocean' template, therefore re-anatomy of the compositions and nature for this region is necessitated. Taking advantage of the methodology and basic principles of plate convergence anatomy and synthesizing previous studies together with our recent research, we may gain new insights into the evolution of the Himalayan orogeny. (1) The Yarlung-Zangbo ophiolite is composed of multiple tectonic units rather than a single terminal suture zone, and a group of different tectonic units were juxtaposed against each other in the backstop of the Gangdese forearc. (2) The Tethyan Himalayan Sequence (THS) contains mélanges with typical block-in-matrix structures, uniform southwards paleocurrents and age spectra of detrital zircons typical of Eurasia continent. All of these facts indicate that the THS belonged to Eurasia plate before the terminal collision, emplaced in the forearc of the Gangdese arc. (3) The Greater Himalayan Crystalline Complex (GHC) and Lesser Himalayan Sequence (LHS) comprise complex components including eclogites emplaced into the GHC and the upper part of the LHS. Judging from the fact that HP-UHP metamorphic rocks are exhumed and emplaced in the upper plate, the GHC and the upper part of the LHS where eclogite occur should be assigned to the upper plate, lying above the terminal subduction zone surface. It is the very surface along which the continuous subduction of the India subcontinent occurred, therefore acting as the terminal, cryptic suture. From the suture further southward, the bulk rock associations of the LHS and Sub-Himalayan Sequence (Siwalik) show little affinity of mélange, probably belonging to the foreland system of the India plate. By the anatomy of tectonic features of all the tectonic units in the Himalayan orogen as well as the ages of the subduction-accretion related deformation, we conclude that the terminal India-Eurasia collision occurred after 14 Ma, the timing of the metamorphism of the eclogites emplaced into the upper plate. The development of rifts stretching in N-S direction in Tibet and tectonic events with the transition from sinistral to dextral movements in shear zones, such as the Ailaoshan fault in East Tibet, can coordinately reflect the scale and geodynamic influence of the India-Eurasia convergence zone. By conducting a detailed anatomy of the southern Himalayas, we propose a new model for the final collision-accretion of the Himalayan orogeny. Our study indicates that the anatomy of structures, composition, and tectonic nature is the key to a better understanding of orogenic belts, which may apply to all the orogenic belts around the world. We also point out that several important issues regarding the detailed anatomy of the structures, compositions and tectonic nature of the Himalayan orogeny in future. [ABSTRACT FROM AUTHOR]

Models that support a single collision scenario for India and Eurasia are incompatible with the evidence that an intra-oceanic island arc (IOIA) existed within the Neotethyan Ocean. Understanding the spatial and temporal extent of any IOIA is crucial for India-Eurasia collision studies as the entire ocean, including any intra-oceanic features, must have been consumed or emplaced prior to continental collision. Here, we review what is known about the Neotethyan IOIA and report evidence from sedimentary successions in NW India and southern Tibet to constrain when and where it was emplaced. We use detrital mineral geochemistry and supporting provenance and age data to identify the source of the sediments and compare the timing of erosion of IOIA-derived material in both regions. Detrital chrome spinels, extracted from distinct sedimentary horizons in southern Tibet (Sangdanlin) and NW India (Ladakh), exhibit similar average geochemical values (TiO 2 = 0.09 and 0.24%, Cr# = 0.66 and 0.68 and Mg# = 0.45 and 0.53, respectively) and supra-subduction zone (SSZ), forearc peridotite signatures. Furthermore, they overlap with in-situ chrome spinels reported from the Spongtang Ophiolite in NW India and the Sangsang Ophiolite in southern Tibet. As with many of the ophiolitic remnants that crop out in and adjacent to the Yarlung-Tsangpo and Indus suture zones (YTSZ and ISZ respectively), the Spongtang and Sangsang ophiolites formed in an IOIA setting. Linking the source of the detrital chrome spinels to those analysed from remnant IOIA massifs in the YTSZ and ISZ is strong evidence for the emplacement of the IOIA onto the Indian margin. The timing of the IOIA collision with India is constrained by the depositional ages of the chrome spinel-bearing sediments to the end of the Paleocene (Thanetian) in southern Tibet and the Early Eocene in NW India. This indirectly provides a maximum age constraint of Late Paleocene-Early Eocene for intercontinental collision between India and Eurasia. Additionally, this study highlights the importance of targeting distinct sedimentary horizons in collision zones to find evidence for discrete tectonic events that may be obfuscated by later collisions. [ABSTRACT FROM AUTHOR]

Mapping of seafloor tectonic fabric in the Indian Ocean, using high-resolution satellite-derived vertical gravity gradient data, reveals an extinct Pacific-style oceanic microplate (‘Mammerickx Microplate’) west of the Ninetyeast Ridge. It is one of the first Pacific-style microplates to be mapped outside the Pacific basin, suggesting that geophysical conditions during formation probably resembled those that have dominated at eastern Pacific ridges. The microplate formed at the Indian–Antarctic ridge and is bordered by an extinct ridge in the north and pseudofault in the south, whose conjugate is located north of the Kerguelen Plateau. Independent microplate rotation is indicated by asymmetric pseudofaults and rotated abyssal hill fabric, also seen in multibeam data. Magnetic anomaly picks and age estimates calculated from published spreading rates suggest formation during chron 21o (∼47.3 Ma). Plate reorganizations can trigger ridge propagation and microplate development, and we propose that Mammerickx Microplate formation is linked with the India–Eurasia collision (initial ‘soft’ collision). The collision altered the stress regime at the Indian–Antarctic ridge, leading to a change in segmentation and ridge propagation from an establishing transform. Fast Indian–Antarctic spreading that preceded microplate formation, and Kerguelen Plume activity, may have facilitated ridge propagation via the production of thin and weak lithosphere; however both factors had been present for tens of millions of years and are therefore unlikely to have triggered the event. Prior to the collision, the combination of fast spreading and plume activity was responsible for the production of a wide region of undulate seafloor to the north of the extinct ridge and ‘W’ shaped lineations that record back and forth ridge propagation. Microplate formation provides a precise means of dating the onset of the India–Eurasia collision, and is completely independent of and complementary to timing constraints derived from continental geology or convergence histories. [ABSTRACT FROM AUTHOR]

Despite several decades of investigations, inferences on the timing and nature of collisions along the Mesozoic–Cenozoic Eurasian margin remain controversial. We assimilate geological and geophysical evidence into a plate tectonic model for the India–Eurasia collision that includes continuously-closing topological plate polygons, constructed from a time-dependent network of evolving plate boundaries, with synthetic plates constructed for now-subducted ocean floor, including back-arc basins that formed on the southern Eurasian margin. Our model is regionally-constrained and self-consistent, incorporating geophysical data from abyssal plains offshore West Australia and East Antarctica, including Jurassic age data from offshore Northwest Australia, limiting much of northern Greater India to a ~ 1000 km-long indenter, originally reaching to the Wallaby–Zenith Fracture Zone. Southern Eurasia and Southeast Asia are riddled with dismembered oceanic arcs indicating long-lived Tethyan intra-oceanic subduction. This intra-oceanic subduction system was well-established from Cretaceous time in the India–Eurasia convergence zone in the NeoTethys, which was consumed during Greater India's northward trajectory towards Eurasia from the Early Cretaceous. Fragments of obducted oceanic crust within the Yarlung-Tsangpo Suture Zone, between India and Eurasia, predominantly date to the Late Jurassic or mid Cretaceous (Barremian–Aptian). The various ophiolites along strike and a hiatus in subduction-related magmatism during the Tithonian–Aptian suggest that there was at least one generation of intra-oceanic arc formation, whose plate boundary configuration remains uncertain. Paleomagnetic and magmatic studies suggest that the intra-oceanic arc was at equatorial latitudes during the Early Cretaceous before subduction resumed further north beneath the Eurasian margin (Lhasa terrane), with another hiatus in subduction-related magmatism along southern Lhasa during ~ 80–65 Ma, possibly as the back-arc spreading centre approached the active Andean-style margin. In our model, Greater India collided with the Tethyan intra-oceanic arc in Paleocene–Eocene time, finally closing the Tethyan seaway from Mid-Late Eocene time, which is consistent with the age of the youngest marine deposits found between India and Eurasia. Geological evidence from the collision zone indicates an age of initial arc–continent collision by ~ 52 Ma, followed by the “soft” (initial) continent–continent collision between India and Eurasia by ~ 44 ± 2 Ma. This timing is supported by marine geophysical data, where the spreading centres in the Indian Ocean record a drastic decline in seafloor spreading rates and changes in spreading directions first at ~ 52 Ma, followed by another reorganisation at ~ 43 Ma. The abandonment of spreading in the Wharton Basin and the onset of extrusion tectonics in Asia by ~ 36 Ma are likely indicators of “hard” (complete) continent collision, and highlight the multi-stage collisional history of this margin. Our continuously evolving network of mid-ocean ridge and subduction zone geometries, and divergence/convergence vectors through time, provide a basis for future refinements to assimilate new data and/or test alternative tectonic scenarios. [ABSTRACT FROM AUTHOR]

The Sanjiang region in SE Tibet Plateau, and the western Yunnan region in southwestern China constitute a collage of Gondwana-derived micro-continental blocks and arc terranes that were accreted together after the closure of the Paleotethys Oceans in Permo-Triassic. The lithospheric structure in Sanjiang prior to the Cenozoic was dominantly characterized by sub-parallel sutures, subduction-modified mantle and crust, Mesozoic basins between the sutures, and primary polymetallic accumulations. During the Cenozoic, intense deformation, episodic magmatism, and diverse mineralization occurred, jointly controlled by the underthrust of South China lithosphere and the subduction of Pacific plate to the east, the India–Eurasia continental collision and the subduction of Indian oceanic plate to the west. In this paper, we identify the following four main phases for the Cenozoic evolution in the Sanjiang region. (i) Subduction and rollback of Neotethyan oceanic plate before ca. 45–40 Ma caused lithosphere shortening, indicated by folding-thrusting in the shallow crust and horizontal shearing in middle crust, and multiple magmatic activities, with associated formation of Sn ore deposits in the Tengchong block, Cu polymetallic ore deposits within Mesozoic basins, and Mo and Pb–Zn ore deposits in the Cangyuan area nearby the Changning–Menglian suture. (ii) Breakoff of Neotethyan slab in 45–40 Ma in combination with the India–Eurasia continental hard collision caused the diachronous removal of the lower lithospheric mantle during 42–32 Ma, with the resultant potassic–ultrapotassic magmatism and formation of the related porphyry–skarn ore deposits along the Jinshajiang–Ailaoshan suture. (iii) Underthrusting of the South China plate resulting in the kinking of Sanjiang, expressed by block rotation, extrusion, and shearing in the southern Sanjiang during 32–10 Ma, with contemporary formation of the orogenic gold deposit along shear zones and the MVT Pb–Zn ore deposits within Mesozoic basins. (iv) Subduction of Indian oceanic plate possibly together with the Ninety East Ridge caused the local extension and volcanism in western Sanjiang, and the interplay between India–Eurasia collision and the Pacific plate subduction induced tensile stress and mantle perturbation in eastern Sanjiang from ca. 10 Ma to present. The Cenozoic tectonic process traces a continuum of lithosphere shortening, sub-lithosphere mantle removal, and lithosphere underthrusting. During the lithospheric mantle removal, the simultaneous melting of the metasomatized lithospheric mantle and juvenile lower crust with possible metal enrichment contributed to the formation of potassic–ultrapotassic intrusive rocks and related porphyry–skarn mineralization. It is proposed that the kinking in the Sanjiang region was controlled by the non-coaxial compressions of the South China block and India continent, which are much larger in size than the blocks in Sanjiang. The underthrust continental lithosphere of the South China block caused the formation of orogenic gold deposits due to the release of metamorphic fluids from the front of the underthrust zone and the development of MVT Pb–Zn deposits via fluid circulation in the farther metal-enriched Mesozoic basins. Our study reveals that the pre-Cenozoic lithospheric structure in Sanjiang played an important role in the styles of tectonic movement, the nature and spatial distribution of magmatism, and the large-scale metallogeny during the Cenozoic. [ABSTRACT FROM AUTHOR]

Evidence for episodic magmatism is found within large batholiths of ancient and modern convergent margin settings and is often attributed to regional geodynamic changes such as an increase in plate convergence rate, lithospheric extension and/or delamination, and intra-crustal/lithospheric shortening. The nature and timing of collision between India and Eurasia remain contentious as many models suggest that the “hard” collision occurred during the Early Paleogene (65 to 45 Ma) whereas other models suggest younger ages (~ 34 Ma) or a diachronous collision. New zircon LA-ICPMS U/Pb ages from rocks of the Ladakh Batholith range from 47.7 ± 0.7 Ma to 57.6 ± 0.7 Ma and correspond to two main episodes of magmatism. The two major episodes of magmatism are correlative to changes in the convergence rate of the Indian and Eurasian plates. The formation of adakitic rocks within the Ladakh Batholith at 49.2 ± 1.2 Ma is facilitated by partial melting of a garnet-bearing thickened lower crust. Therefore we suggest that crustal thickening was initiated by the “hard” collision between India and Eurasia. The convergence slowdown is concurrent with an increase in magmatism within the Ladakh Batholith. Thus the collision is constrained by the decreasing convergence rates at ~ 52 Ma and formation of the adakitic rocks at ~ 49 Ma. [ABSTRACT FROM AUTHOR]

The Hahaigang W–Mo polymetallic skarn deposit is located in the central-eastern part of Gangdese tectono-magmatic belt in Lhasa terrane, Tibet. The deposit was discovered in 2007 with currently proven 46milliontons of WO3 ores, 12milliontons of Mo ores, and 1.31milliontons of combined Cu–Pb–Zn ores, at an average grade of 0.20% WO3, 0.07% Mo, 0.026% Cu, 0.49% Pb, and 3.1% Zn. Ore bodies occur in veins or disseminations, and are confined within the NE-striking Dalong fault zone which is hosted by the Lower-Permian Pangna Group of dominantly quartz sandstone and slate. Several granitic plutons are exposed in the area or known from drill-holes. Ages of these granitic plutons are determined by using zircon U–Pb LA–ICP–MS method. For example, the biotite monzogranite yields a 206Pb/238U–207Pb/238U concordia age of 58.66±0.90Ma and a weighted mean 206Pb/238U age of 57.02±0.42Ma. The granite porphyry yields a 206Pb/238U–207Pb/238U concordia age of 109.1±8.9Ma and a weighted mean 206Pb/238U age of 114.0±2.6Ma. The biotite monzogranite yields a weighted mean 206Pb/238U age of 56.1±1.1Ma. Re–Os isochron age of 63.2±3.2Ma from 5 molybdenite samples collected from the W–Mo skarn ores is also obtained in this study. The zircon U–Pb and molybdenite Re–Os geochronological data suggest that the W–Mo mineralization was not temporally associated with any of the dated igneous plutons. However, the molybdenite Re–Os age of 63.2±3.2Ma indicates that the W–Mo mineralization might have occurred during the main India–Eurasia collision that was initiated around 65Ma. Microprobe analysis of ilvaite that occurs in two generations in the W–Mo skarn ores reveals a close relationship to Ca–Fe–F-rich hydrothermal fluids, which were probably derived from deeply-seated magmas. We suggest that ascent of the fluids was strictly controlled by the ore-controlling Dalong fault zone, and that chemical interaction and metasomatism between the fluids and the Lower-Permian Pangna quartz-feldspathic host rocks produced the ilvaite and the W–Mo polymetallic skarn deposit during the main India–Eurasia collision. Although the majority of the polymetallic deposits in the Gangdese belt are reported to be either pre- or post-main collision, it is evident from this study that the main collision also produced W–Mo polymetallic mineralization within the belt. [ABSTRACT FROM AUTHOR]

Abstract: Large-scale intraplate deformation of the crust and the lithosphere in Central Asia as a result of the indentation of India has been extensively documented. In contrast, the impact of continental collision between Arabia and Eurasia on lithosphere tectonics in front of the main suture zone, has received much less attention. The resulting Neogene shortening and uplift of the external Zagros, Alborz, Kopeh Dagh and Caucasus Mountain belts in Iran and surrounding areas is characterised by a simultaneous onset of major topography growth at ca. 5Ma. At the same time, subsidence accelerated in the adjacent Caspian, Turan and Amu Darya basins. We present evidence for interference of lithospheric folding patterns induced by the Arabian and Indian collision with Eurasia. Wavelengths and spatial patterns are inferred from satellite-derived topography and gravity models. The observed interference of the patterns of folding appears to be primarily the result of spatial orientation of the two indenters, differences in their convergence velocities and the thermo-mechanical structure of the lithosphere west and east of the Kugitang–Tunka Line. [Copyright &y& Elsevier]

Abstract: Based on a detailed analysis of satellite imagery combined with field geologic and geomorphic observations, we have mapped late Cenozoic folds and faults in the northeastern Pamir–Tian Shan convergence zone. It is a unique example to understand intracontinental ongoing mountain building within India–Eurasia collision system. In the front of northeastern Pamir, our investigations reveal that the NW-WNW-trending folds display a right-stepping en echelon pattern and NW-WNW-striking faults are mainly characterized by south-dipping thrusts with an extensive dextral strike-slip component. Drainage systems across the active faults show a systematic right-lateral offset. In contrast, structural style of the ENE trending fold-and-thrust belts are predominated by south–north directed shortening southwest of the Tian Shan. Our results also infer that oblique thrusting accommodates as long-term dextral slip rate of ca. 4.0mm/yr during the late Cenozoic time north of the Pamir topographic front. Tectono-stratigraphic evidence suggests that the tectonic deformation was initiated at ca. 3–5Ma in the study area. We suggest that intracontinental mountain building in the Pamir–Tian Shan convergence zone should be attributed to the crustal shortening caused by folding and thrusting as well as block rotation related to strike-slip faulting within the India–Eurasia collision system. [Copyright &y& Elsevier]

Reconstructions of the relative positions of the India and Eurasia plates, using recently revised histories of movement between India and Somalia and between North America and Eurasia and of the opening of the East African Rift, show that India's convergence rate with Eurasia slowed by more than 40% between 20 and 10 Ma. Much evidence suggests that beginning in that interval, the Tibetan Plateau grew outward rapidly and that radially oriented compressive strain in the area surrounding Tibet increased. An abrupt increase in the mean elevation of the plateau provides a simple explanation for all of these changes. Elementary calculations show that removal of mantle lithosphere from beneath Tibet, or from just part of it, would lead to both a modest increase in the mean elevation of the plateau of ∼1 km and a substantial change in the balance of forces per unit length applied to the India and Eurasia plates. [ABSTRACT FROM AUTHOR]

A portable broadband seismic array was deployed from the northeast Tibetan Plateau to the southwest Ordos block, China. The seismic structure of the crust and uppermost mantle of the Liupanshan area is obtained using receiver function analysis of teleseismic body waves. The crustal thickness and Poisson’s ratios are estimated by stacking the weighted amplitudes of receiver functions. Our results reveal complex seismic phases in the Liupanshan area, implying intense deformation at the boundary between the Tibetan Plateau and the Ordos block. The average crustal thickness is 51.5 km in the northeast Tibetan Plateau, 53.5 km in the Liupan Mountain and 50 km in the southwest Ordos block, resulting in a concave Moho beneath the Liupan Mountain. The Poisson’s ratio of the Liupanshan area varies between 0.27–0.29, higher than the value of 0.25–0.26 to the east and west of the Liupan Mountain, suggesting partial melting in the lower crust. The variance in Poisson’s ratio across the Liupan Mountain indicates notable changes in the crustal composition and mechanical properties, which may be formed by the northeastward flow of the Tibetan lower crust during the India-Eurasia collision. [ABSTRACT FROM AUTHOR]

Active intraplate deformation of the India–Australia Plate is now being captured by far-field global positioning system (GPS) measurements as well as measurements on a few islands located within the deforming zone itself. In this paper, we combine global and regional geodetic solutions with focal mechanisms of earthquakes to derive the present-day strain field of the India–Australia Plate. We first compile an updated catalogue of 131 Indian intraplate earthquakes spanning the period between the two Asian mega earthquakes of Assam 1897 and Sumatra 2004. Using Haines and Holt's numerical approach applied to a fully deformable India–Australia Plate, we show that the use of GPS data only or earthquakes data only has severe drawbacks, related, respectively, to the small number of stations and the incompleteness of the earthquakes catalogue. The combined solution avoids underestimation of the strain inherent to the Kostrov summation of seismic moments and provides details that cannot be reached by pure GPS modelling. We further explore the role of heterogeneity of the India–Australia Plate and find that the best model, in terms of geodetic vectors fit, relative distribution of strain, style and direction of principal strain from earthquakes, is obtained using the surface heat-flow as a proxy for rheological weakness of the oceanic lithosphere. The present-day deformation is distributed around the Afanasy Nikitin Chain in the Central Indian Basin (CIB)—where it is almost pure shortening—and within the Wharton Basin (WB) off Sumatra—where it is almost pure lateral strike-slip. The northern portion of NinetyEast ridge (NyR) appears as a major discontinuity for both strain and velocity. The new velocity field gives an India/Australia rotation pole located at overlapping with previous solutions, with continental India moving eastward at rates ranging from 13 mm yr−1 (southern India) to 26 mm yr−1 (northern India) with respect to Australia. Taking into account the intraplate velocity field in the vicinity of the Sumatra trench, we obtain a convergence rate of 46 mm yr−1 towards N18°E at the epicentre of the 2004 Aceh megaearthquake. The predicted instantaneous shortening in the CIB and WB and extension near Chagos-Laccadive are in good agreement with the finite deformation measured from plate reconstructions and seismic profiles, suggesting a continuum of deformation since the onset of intraplate deformation around 7.5–8 Ma. Since no significant change in India convergence is detected at that time, we suggest that the intraplate deformation started with the trenchward acceleration of Australia detaching from India along a wide left-lateral oceanic shear band activating the NyR line of weakness as well as north–south fracture zones east of it. The predicted total amount of left lateral finite strain along these faults is in the range 110–140 km. [ABSTRACT FROM AUTHOR]

Abstract: A number of previous models have been proposed to explain the formation of the South China Sea, the largest marginal sea basin in Southeast Asia, but no consensus has been reached. In this work, two-dimensional (2D) plan-view models (linear viscous rheology) are constructed to simulate the India–Eurasia collision, its resultant intra-plate deformation and lateral motion along the Red River Fault. We then use 2D cross-section models (a combination of linear viscous rheology and elastic–plastic rheology) to simulate the influence of deep asthenosphere upwelling on lithospheric deformation. The plan-view models show that the India–Eurasia collision can result in extensive east-southeastward tectonic extrusion, consistent with the prediction of the analogue experiments. During extrusion, the modelled Red River Fault first experienced huge left-lateral shearing and then changed to right-lateral shearing (reversal). The style of shearing motion along the Red River Fault is a function of the distance between the fault and the India–Eurasia collision frontier, which decreases with time and controls relative extrusion movement between the South China Block and Indochina Block. Our models also show that the extrusion can generate extension in an approximately N-S direction in the region containing the present-day South China Sea. Our cross-section models further demonstrate that such horizontal extension can only generate limited thinning of the continental lithosphere in the South China Sea region. In contrast, asthenosphere upwelling is much more efficient in generating lithospheric upper mantle thinning but still inefficient for crust thinning. It is the combination of mechanical extension and asthenosphere upwelling that proves to be the most efficient way to thin the entire lithosphere, and that represents the most likely driving mechanism for the opening and spreading of the South China Sea. [Copyright &y& Elsevier]

Abstract: Using a dynamic method, we present a quantitative model for the present-day crustal movement in China. We consider not only the effect of the India–Eurasia collision, the gravitational potential energy difference of the Tibet Plateau, but also the contribution of the shear traction on the bottom of the lithosphere induced by the global mantle convection. By solving a system of force balance equations using a finite element method, we obtain the crustal movement velocity in China with respect to the Eurasia plate. The comparison between our result and the velocity field obtained from the GPS observation shows that our model satisfactorily reproduces the general picture of crustal deformation in China. Numerical modeling results reveal that the shear traction at the base of the lithosphere induced by the mantle flow is probably a considerable factor that causes the movement and deformation of the lithosphere in China continent. But its effect focus on the eastern China. [Copyright &y& Elsevier]

Approximately 2200 magnetic anomaly crossings and 800 fracture zone crossings flanking the Carlsberg ridge and Central Indian ridge are used to estimate the rotations of the Indian and Capricorn plates relative to the Somalian Plate for 20 distinct points in time since 20 Ma. The data are further used to place limits on the locations of the northern edge of the rigid Capricorn Plate and of the southern edge of the rigid Indian Plate along the Central Indian ridge. Data south of and including fracture zone N (the fracture zone immediately south of the Vema fracture zone), which intersects the Central Indian ridge near 10°S, are well fit assuming rigid Capricorn and Somalian plates, while data north of fracture zone N are not, in agreement with prior results. Data north of fracture zone H, which intersects the Central Indian ridge near 3.2°S, are well fit assuming rigid Indian and Somalian plates, while data south of and including fracture zone H are not, resulting in a smaller rigid Indian Plate and a wider diffuse oceanic plate boundary than found before. The data are consistent with Capricorn–Somalia motion about a fixed pole since≈8 Ma, but require rotation about a pole 15° farther away from the Central Indian ridge from 20 to≈8 Ma. The post-8-Ma pole also indicates Capricorn–Somalia displacement directions that are 7° clockwise of those indicated by the pre-8-Ma stage pole. In contrast, India–Somalia anomaly and fracture crossings are well fit by a single fixed pole of rotation for the past 20 Ma. India–Somalia motion has changed little during the past 20 Myr. Nonetheless, astronomically calibrated ages for reversals younger than 12.9 Ma allow resolution of the following small but significant changes in spreading rate: India–Somalia spreading slowed from 31 to 28 mm yr−1 near 7.9 Ma and later sped up to 31 mm yr−1 near 3.6 Ma; Capricorn–Somalia spreading slowed from 40 to 36 mm yr−1 near 11.0 Ma, later sped up to 38 mm yr−1 near 5.1 Ma and further sped up to 40 mm yr−1 near 2.6 Ma. The motion between the Indian and Capricorn plates is estimated by differencing India–Somalia and Capricorn–Somalia rotations, which differ significantly for all 20 pairs of reconstructions. India has rotated relative to the Capricorn Plate since at least≈20 Ma. If about a pole located near 4°S, 75°E, the rate of rotation was slow,(95 per cent confidence limits), from 20 to 8 Ma, but increased to(95 per cent confidence limits) at≈8 Ma. The onset of more rapid rotation coincides, within uncertainty, with the inferred onset at 7–8 Ma of widespread thrust faulting in the Central Indian basin, and with the hypothesized attainment of maximum elevation and initiation of collapse of the Tibetan plateau at≈8 Ma. The plate kinematic data are consistent with steady India–Capricorn motion since 8 Ma and provide no evidence for previously hypothesized episodic motions during that interval. The convergence since 8 Ma between the Indian and Capricorn plates significantly exceeds (by 13 to 20 km) the convergence estimated from three north–south marine seismic profiles in the Central Indian basin. Where and how the additional convergence was accommodated is unclear. [ABSTRACT FROM AUTHOR]

Although the Altyn Tagh Fault (ATF) is thought to play a key role in accommodating India-Eurasian convergence, little is known about its earthquake history. Studies of this strike-slip fault are important for interpretation of the role of faulting versus distributed deformation in the accommodation of the India- Eurasia collision. In addition, the > 1200 km long fault represents one of the most important and exemplary intracontinental strike-slip faults in the world. We mapped fault trace geometry and interpreted paleoseismic trench exposures to characterize the seismogenic behavior of the ATF. We identified 2 geometric segment boundaries in a 270 km long reach of the central ATF. These boundaries define the westernmost Wuzhunxiao, the Central Pingding, and the easternmost Xorxol (also written as Suekuli or Suo erkuli) segments. In this paper, we present the results from the Camel paleoseismic site along the Xorxol Segment at 91.759°E, 38.919°N. There evidence for the last two earthquakes is clear and 14C dates from layers exposed in the excavation bracket their ages. The most recent earthquake occurred between 1456 and 1775 cal A.D. and the penultimate event was between 60 and 980 cal A.D. Combining the Camel interpretations with our published results for the central ATF, we conclude that multiple earthquakes with shorter rupture lengths (?? 50 km) rather than complete rupture of the Xorxol Segment better explain the paleoseismic data. We found 2-3 earthquakes in the last 2-3 kyr. When coupled with typical amounts of slip per event (5-10 m), the recurrence times are tentatively consistent with 1-2 cm/yr slip rates. This result favors models that consider the broader distribution of collisional deformation, rather than those with northward motion of India into Asia absorbed along a few faults bounding rigid blocks.

The Tian Shan, east–west trending more than 2000 km, is one of most active intracontinental mountain building belts that resulted from India–Eurasia collision during Cenozoic. In this study, Quaternary folding related to intracontinental mountain building of the Tian Shan orogenic belt is documented based on geologic interpretation and analyses of the satellite remote sensing images [Landsat Thematic Mapper (TM)/Enhanced Thematic Mapper (ETM) and India Remote Sensing (IRS) Pan] combined with field geologic and geomorphic observations and seismic reflection profiles. Analyses of spatial–temporal features of Quaternary folded structure indicate that the early Quaternary folds are widely distributed in both piedmont and intermontane basins, whereas the late Quaternary active folds are mainly concentrated on the northern range-fronts. Field observations indicate that Quaternary folds are mainly characterized by fault-related folding. The formation and migration of Quaternary folding are likely related to decollement surfaces beneath the fold-and-fault zone as revealed by seismic reflection profiles. Moreover, analysis of growth strata indicates that the Quaternary folding began in late stage of early Pleistocene (2.1–1.2 Ma). Finally, tectonic evolution model of the Quaternary deformation in the Tian Shan is presented. This model shows that the Quaternary folding and faulting gradually migrate toward the range-fronts due to the continuous compression related to India–Eurasia collision during Quaternary time. As a result, the high topographic relief of the Tian Shan was formed. [Copyright &y& Elsevier]

The Pamir indentor of the northwestern Himalayan syntaxis is a first-order feature demonstrating partly the northward extent of deformation due to the Cenozoic Indo-Eurasia collision. The Alai Valley of Kyrgyzstan at the northern end of the indentor is a strategically positioned, E-W trending intramontane basin that constrains the timing and extent of crustal deformation in this area of the collision zone. To quantify the convergence accommodated across the Alai Valley during the Late Cenozoic, we collected structural and stratigraphic field data, reviewed existing Soviet literature, and analyzed migrated seismic reflection profiles to construct and restore two regional sections crosscutting the basin. Our study suggests that the development, progressive closure, and conversion of this formerly marine basin into a terrestrial intramontane basin result from two main deformation events: (1) Distributed north-south contraction took place during the late Oligocene-early Miocene, accommodated one third to half of the total shortening and was followed by the formation of a regional erosion surface; and (2) N-S shortening resumed in the mid-Miocene and continues today. During this second episode the thrust front migrated southward, localized along the Trans Alai ranges, and failed to reactivate earlier Neogene structures. Horizontal shortening of about 35% across the Alai Valley implies relatively low strain rates and displacement rates of about 4.18-4.69 × 10−16 s−1 and 0.66-0.78 mm yr−1, respectively, for the last 25 Myr. Our study confirms other regional observations indicating that contractional deformation occurred far in the interior of the Asian continent as early as the late Oligocene. [ABSTRACT FROM AUTHOR]

Late Quaternary right-lateral displacement and slip rates have been determined along WNW–ESE-trending active faults in the intermontane Yanqi Basin on the southeastern flank of the Chinese Tian Shan. Detailed analyses of satellite images and field investigation have revealed that the active Kaidu River fault zone on the southern margin of the basin is a strike–slip fault zone. Drainage systems incising late Pleistocene–Holocene alluvial fans record between 3 and 250 m dextral offsets and show progressive displacement along the fault zone. Fault scarps developed in the alluvial fans range in height from 1 to 25 m and alternate along the strike of the fault zone from northeast to southwest facing in a left-stepping en echelon pattern. Based on the offset of stream channels, 14C dates of alluvial deposits, and fabrics within fault rocks, we infer that (1) the average right-lateral slip rate is about 8 mm/year, with a vertical component of 1 mm/year, (2) the offset produced by individual seismic faulting event is typically 3–7 m, (3) the average recurrence interval of large seismic events (M>7) is ca. 500 years, and (4) the most recent movement occurred during the past 2.5 ky in the Kaidu River fault zone. These strike–slip faults represent partitioning of horizontal slip within an otherwise thrust dominated orogen related to the India–Eurasia collision within the Tian Shan during late Quaternary. [Copyright &y& Elsevier]

The East Asian continental margin straddles the boundary between the Pacific Subduction Domain to the east and the Tethyan Collision Domain to the west. The spatial and temporal interaction between these two dynamic domains induced a dextral trans-tensional stress field, generating nearly 75% of the globe's marginal seas and continental margin rifts during the Cenozoic. Among these, the South China Sea (SCS) and its northern margin are located in the core of the Pacific Subduction Domain and the Tethyan Collision Domain. The evolution of the SCS and its northern margin are of prime interest because of their spectacular magnetic lineations and strong rifting. In spite of the several investigations carried out on the Cenozoic marginal seas and rift basins, their formation mechanisms remain equivocal. Here we perform a comprehensive analysis of seismic profiles and fault architecture data with a view to understand the Cenozoic tectonic evolution of the northern margin of the SCS. Based on detailed structural analysis of the geometry and kinematics, we demonstrate that the NE- and ENE-striking faults assembled to horsetail- or feather-shaped structures in plan view, which display flower-like structures in seismic profiles. Two stages of faulting along NE-trending faults are identified along the northern margin of the SCS. The earlier oblique extension occurred during the Paleocene to the early Middle Eocene (~44–42 Ma), accompanied by strong rifting and formation of some left-step en echelon -like faults. The later trans-tensional faulting developed during the late Middle Eocene to the Early Miocene (~21 Ma), resulting in the formation of the dextral right-step trans-tensional fault system. Two stages of faulting were linked to the joint effect among the Indo-Eurasian collision to the west, the subduction of the Pacific Plate to the east and the slab pull of the proto-SCS to the south. Our study provides important insights into the dynamics and tectonics controlling the opening of the South China Sea. During the Late Eocene to the Oligocene, the dextral trans-extensional faulting along the right-step strike-slip fault system caused the opening of the Northwest Sub-basin, the East Sub-basin and the Northeast Sub-basin. However, during the Early Miocene, the sinistral strike slipping of the Ailao Shan-Red River (ASRR) shear zone and the slab-pull force of the proto-SCS resulted in the opening of the Southwest Sub-basin and the change of the spreading direction of the East Sub-basin. [ABSTRACT FROM AUTHOR]

• First calcite U-Pb geochronlogy on tectonic veins in Thailand. • Timing of calcite precipitation is constrained to Indosinian II and Cenozoic. • Redox-sensitive element maps are used to decipher U-Pb data. U-Pb dating of calcite veins allows direct dating of brittle deformation events. Here, we apply this method to hydrothermal calcite veins in a fold-and-thrust belt and a large scale strike-slip fault zone in central and western Thailand, in an attempt to shed new light on the regional upper crustal deformation history. Calcite U-Pb dates for the Khao Khwang Fold and Thrust Belt (KKFTB) of 221 ± 7 Ma and 216 ± 3 Ma demonstrate that calcite precipitated during tectonic activity associated with stage II of the Indosinian Orogeny (Late Triassic – Early Jurassic). One additional sample from the KKFTB suggests that the Indosinian calcite has locally been overprinted by a Cenozoic fluid event with a different chemistry. For the Three Pagodas Fault Zone (TPFZ), our calcite U-Pb results suggest a complex, protracted history of Cenozoic brittle deformation. Petrographic information combined with contrasting redox-sensitive trace elemental signatures suggest that the vein arrays in the TPFZ precipitated during two distinct events of brittle deformation at ~48 and ~23 Ma. These dates are interpreted in the context of far-field brittle deformation related to the India-Eurasia collision. The presented calcite U-Pb dates are in excellent agreement with published age constraints on the deformation history of Thailand, demonstrating the utility of the method to decipher complex brittle deformation histories. The paper further illustrates some of the complexities in relation to calcite U-Pb dating and provides suggestions for untangling complex datasets that could be applied to future studies on the deformation history of Thailand and other regions. [ABSTRACT FROM AUTHOR]