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The controversial history of Indian subduction beneath Asia is crucial to understand the Himalayan orogeny and more in general the geodynamic process of continental subduction. New key information is here presented from the Oligocene‐Pliocene Shiquanhe Basin located in the southwestern Tibetan Plateau. The alluvial‐fan, lacustrine, and braided‐river sediments of the Oligocene Rigongla Formation were non‐conformably deposited onto the Upper Cretaceous Gangdese granitoid rocks and fed from erosion of the batholith itself and of associated Paleogene Linzizong volcanic rocks. Stratigraphic evidence testifies to the development of an orogen‐parallel intracontinental rift along the retro‐side of the Gangdese arc in the Oligocene, at the same time as the Kailas basin formed along the pro‐side of the Gangdese arc. The subsidence of these twin basins may have been caused by steepening of the subducting Indian continental slab or by the passage of a wave of dynamic topography during continuing subduction. Plain Language Summary: The convergence and collision of India and Asia leading to the formation of the Himalayan Mountains and Tibetan Plateau ("the roof of the world") is one of the most significant geological events of the Cenozoic Era. Geophysical data show that rocks of the Indian continent lie beneath southern Tibet, but the early subduction history of India related to the initial topographic grow of the Himalaya remains unclear. We studied the Shiquanhe Basin in southwestern Tibet to investigate the continent's subduction history using stratigraphic, sedimentological, and provenance analyses. Our results indicate that an orogen‐parallel rift developed in southern Tibet during the Oligocene Epoch. Challenging earlier beliefs, we propose two alternative models to explain such event of tectonic extension: steepening of subduction angle or passage of a topographic wave across the subducting plate. The latter hypothesis would also explain the widespread uplift and lack of Oligocene sedimentary deposits recorded all across the front of the Himalayan range. Key Points: Oligocene Rigongla Fm. testifies to orogen‐parallel extension along retro‐side of Gangdese arcShiquanhe Basin passed from extension to compression in Oligocene to Miocene timesOligocene extension was caused by change of Indian subduction angle or wave of dynamic topography [ABSTRACT FROM AUTHOR]

The Yarlung Tsangpo, draining the Himalayan‐Tibetan orogen along the Indus‐Yarlung suture zone, receives detritus from the deformed remnants of both Indian margin to the south and Asian margin to the north. High resolution petrographic, heavy‐mineral and geochemical datasets, combined with published geochronological data, allow us to monitor compositional changes, estimate erosion rates and investigate lithologic, climatic and anthropic controls on sediment fluxes along this large sediment‐routing system entirely developed within high mountain areas. Sediment generated from the Lhasa Block along the southern margin of Asia is characterized by abundant feldspar and volcanic rock fragments, amphibole‐dominated transparent heavy mineral suite and high concentrations of K, Rb, Be, Th and Pb. Himalayan‐derived sand, instead, is characterized by sedimentary to low‐rank metasedimentary rock fragments, poor transparent heavy mineral suite dominated by durable recycled (zircon, tourmaline) or metamorphic minerals (chloritoid, garnet) and high Ca concentration. Sand from the ophiolitic suture is distinguished by serpentinite grains and mafic volcanic or metavolcanic detritus, transparent heavy mineral suite including olivine, Cr‐spinel, enstatite and clinopyroxene, and high Mg, Cr, Ni and low rare earth elements. Himalayan detritus is prominent in Yarlung Tsangpo upper reaches, whereas detritus from the Lhasa Block becomes progressively predominant in the middle and lower reaches. Provenance budgets based on integrated petrographic, heavy‐mineral and geochemical datasets indicate that ca. 83% of the detritus is supplied by the Lhasa Block and the rest mostly from the Himalaya (ca. 12%) and subordinately from the ophiolitic suture (5%). A low average erosion rate of ca. 0.06 mm/a was estimated for the Yarlung Tsangpo catchment upstream of the Namche Barwa syntaxis, which resulted from dry climate, relatively mild average relief and sediment storage in wide valley tracts of the middle and lower reaches. The decrease in sediment flux recorded in recent decades is mainly ascribed to growing human activities, which are becoming a prominent control on sediment generation and transportation even in the high‐mountain area of South Tibet. [ABSTRACT FROM AUTHOR]

Mesozoic oceanic anoxic events were characterized by relatively low seawater sulphate concentrations ([SO42−$$ {{\mathrm{SO}}_4}^{2-} $$]), which likely regulated the development and evolution of these major palaeoceanographic phenomena. However, there is little reliable sedimentary evidence for low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] in ancient marine waters and understanding of how such a seawater chemistry potentially impacted oceanic anoxic events is limited. This study presents an integrated sedimentological, mineralogical and geochemical investigation of the mineral siderite hosted in dark grey shale and sideritic concretions of Early Aptian (coeval with Oceanic Anoxic Event 1a) from the Tibetan Himalaya. Siderite is present throughout the section and possesses similar morphological characteristics whether in dark grey shale or concretions. Siderite can be present as disseminated and rhombic crystals formed during early diagenesis, or minor spherical crystals formed during late diagenesis. The evidence from redox elements, middle rare‐earth element bulge patterns and extremely low carbon‐isotope values of the sideritic concretions indicates that the iron carbonate was formed in the Fe‐reduction zones by the process of dissimilatory iron reduction. This process would have required conditions of low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$], reducing environment, abundant iron and high alkalinity. Additionally, the coexistence of siderite and pyrite may indicate that dissimilatory iron reduction occurred close to the microbial sulphate reduction zone, with seawater [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] hovering around the tipping point at which pyrite could form once seawater sulphate increased. Such an increase during Oceanic Anoxic Event 1a could have resulted from basalt–seawater interaction and associated enhanced continental weathering, and/or hydrothermal activity. This study's observations support the previous hypothesis that low [SO42−$$ {{\mathrm{SO}}_4}^{2-} $$] for Oceanic Anoxic Event 1a was probably caused by massive gypsum burial in the proto‐South Atlantic. Subsequently, enhanced sulphate input could have promoted microbial sulphate reduction and accompanying oxidation of organic matter, which likely further enhanced nutrient recycling, increased primary productivity and organic‐carbon burial, leading to more oxygen consumption and expansion of oxygen minimum zones, as reconstructed for many oceanic anoxic events. [ABSTRACT FROM AUTHOR]

The early Toarcian of the Early Jurassic saw a long-term positive carbon-isotope excursion (CIE) abruptly interrupted by a significant negative excursion (n CIE), associated with rapid global warming and an oceanic anoxic event (T-OAE, ∼183 Ma). However, the detailed processes and mechanisms behind widespread ocean deoxygenation are unclear. Here, we present high-resolution carbonate-associated sulfate sulfur-isotope (δ 34 S CAS) records spanning the late Pliensbachian–Toarcian (Pl–To) interval from the Tibetan Himalaya. We observe a large positive sulfur-isotope excursion (SIE) from ∼20‰ (around the Pl–To boundary) to ∼40‰ (around the end of the T-OAE n CIE), attributed to large-scale burial of reduced sulfur (pyrite and sulfurized organic matter) under widespread anoxic/euxinic conditions. Importantly, high δ 34 S CAS values were maintained into the mid–late Toarcian, even when global anoxic conditions diminished. The δ 34 S data confirm significant spatial heterogeneity in seawater δ 34 S compositions during the whole of the Toarcian, and provide strong evidence for a two-phase pattern of ocean deoxygenation. Upwelling of 34S-enriched equatorial deep water, affected by significant reduced-sulfur burial, likely caused the greatly amplified SIE in the formerly adjacent Tibetan area. By contrast, the dampened magnitude of the Toarcian SIE in Europe is attributed to a smaller, local reduced-sulfur sink. Box-modeling results indicate that the persistent post-T-OAE positive δ 34 S values were likely maintained because of a global reduction in Ca-sulfate (gypsum and anhydrite) burial driven by declining and continuously low seawater sulfate concentrations during and after the T-OAE. This geochemical pattern, albeit markedly reducing the total amount of global pyrite sequestration, increased the proportion of reduced to oxidized sulfur burial needed to generate the observed positive δ 34 S values. • Spatial heterogeneity in seawater δ 34 S during the entire Toarcian. • A long-term, two-phase pattern of ocean deoxygenation in the early Toarcian. • Post-T-OAE positive δ 34 S values were likely maintained by negligible gypsum burial. • The upwelling of 34S-enriched deep water likely caused the amplified SIE in Tibet. [ABSTRACT FROM AUTHOR]

This study presents a detailed stratigraphic record of the Paleocene–Eocene Thermal Maximum (PETM) in the Gamba area of the Tethyan Himalaya, a carbonate-platform succession originally deposited along the southern margin of the eastern Tethys Ocean. The Paleocene-Eocene boundary interval is marked by a negative carbon isotope excursion at the boundary between members 3 and 4 of the Zongpu Formation. The succession is erosionally truncated at this surface, which is overlain by an intraformational carbonate conglomerate, and only the upper part of the PETM interval is preserved. Foraminiferal assemblages of Shallow Benthic Zone 4 are present below the conglomerate bed, but are replaced by assemblages of Shallow Benthic Zone 6 above the conglomerate. Depositional facies also change across this surface; below the disconformity, floatstones and packstones containing nummulitid forams record progressive transgression in an open-marine environment, whereas restricted or lagoonal inner-ramp deposits containing Alveolina and Orbitolites are typical above the disconformity. The prominent negative excursion observed in the δ 13 C of whole-rock carbonate (− 1.0‰ at Zongpu, − 2.4‰ at Zengbudong) and organic matter (− 24.7‰, at Zengbudong) is correlated to the characteristic PETM carbon isotope excursion. This major negative excursion in shallow-marine carbonates may have partly resulted from syndepositional alteration of organic matter. The erosional unconformity can be constrained to the lower PETM interval (between 56 and 55.5 Ma), and is identifiable throughout the Tethyan Himalaya. This widespread disconformity is attributable to tectonic uplift associated with the southward migration of an orogenic wave, originated 3 ± 1 Ma earlier in the middle Paleocene at the first site of India-Asia continent-continent collision. A possible eustatic component of the pre-PETM sea-level fall, which resulted in the excavation of incised valleys filled during the subsequent sea-level rise when the conglomerate bed was deposited, remains to be assessed. [ABSTRACT FROM AUTHOR]

The early Toarcian, as registered in a variety of sedimentary archives, was characterized by an abrupt negative carbon-isotope excursion (CIE) typically superimposed on a long-term positive trend, and was accompanied by significant climatic and environmental changes. However, the changes in continental weathering influx and oceanic deoxygenation in shallow waters and their possible role in causing carbonate-platform crises in low latitudes remains poorly constrained. Here, we present carbonate content and carbonate-hosted elements for the Pliensbachian–Toarcian transitional interval from the Kioto Carbonate Platform (KCP) in the Tibetan Himalaya. The most water-insoluble elements (e.g. Ti, Sc, Th and total rare earth elements) show an obvious increase starting at the Pliensbachian–Toarcian boundary, followed by a weak increase or relatively high-level values during the negative phase of the T-OAE CIE, suggesting that the enhanced terrigenous input can be linked to rapid global warming during this time interval. The Mn, Ce and Ce anomaly start to increase immediately following the rise in abundance of the water-insoluble elements, followed in turn by enhanced values over the interval of the negative CIE. These observations indicate that the deoxygenation process and development of manganous (suboxic) conditions occurred in shallow water during this time interval and were likely linked to enhanced continental weathering and nutrient input, favoring both primary productivity and oxygen consumption. Stratigraphically higher, the water-insoluble elements show a gradual decreasing trend parallel with elevated values of redox proxies during the recovery phase of the CIE, suggesting decline in continental weathering intensity and a corresponding second deoxygenation in shallow waters. In this instance, deoxygenation might have been caused by a slackening of ocean circulation and/or enhanced recycling of bioessential nutrients. The coupled relationship between biotic changes, carbonate content and geochemical data suggest that: (1) the onset of enhanced terrigenous influx and deoxygenation in shallow waters likely led to slight deterioration to the KCP around Pliensbachian–Toarcian boundary time, and (2) the drastically enhanced terrigenous flux and deoxygenation likely played a pivotal role in the more severe crisis for benthic carbonate producers during the negative phase of the CIE. • Continental weathering proxies start to rise at Pl–To boundary, followed by high values in the negative T-OAE CIE interval. • Redox proxies increase immediately following weathering proxy rise, followed by enhanced values in the T-OAE CIE interval. • Relationship between proxies of continental weathering and redox suggests a deoxygenation driven by enhanced primary productivity. • Enhanced continental weathering and deoxygenation could have triggered the carbonate-platform crises before and during the T-OAE CIE. • A decline in continental weathering intensity and corresponding deoxygenation occurred in the recovery T-OAE CIE interval. [ABSTRACT FROM AUTHOR]

Abstract: The geochemistry of detrital chromian spinels is commonly used to discriminate provenance from different tectonic settings of mafic and ultramafic igneous rocks. Detrital spinels in Cenozoic foreland-basin successions fed from the Himalaya Orogen were assertively interpreted as sourced from the ophiolitic rocks of the Indus-Yarlung suture zone. This study compares the geochemistry of detrital Cr-spinels from the Tethys Himalaya passive margin and Cretaceous Xigaze forearc successions with those from the Indus-Yarlung ophiolites. Cr-spinels in the Indus-Yarlung ophiolites have low TiO2 (mostly <0.2%) and high Al2O3 (10–48%). Detrital Cr-spinels from the Tethyan Himalaya have instead high TiO2 (mostly >0.2%) and low Al2O3 (mainly 6–23%), indicating a rift-related basaltic origin. Detrital Cr-spinels from the Xigaze forearc basin have either low TiO2 (mostly <0.2%) and low Al2O3 (4–34%), suggesting provenance from a supra-subduction-zone peridotite, or high TiO2 (>1.0%), indicating intra-plate basaltic origin. Compositional fingerprints of detrital Cr-spinels from Lower Eocene foreland-basin strata in the central-eastern Himalaya indicate provenance from the Lhasa Block without input from the Indus-Yarlung ophiolites. Only Cr-spinels from the Lower Eocene foreland-basin strata in the north-western Himalaya and the Upper Eocene–Lower Miocene remnant-ocean turbidites of the Bengal basin are mostly ophiolite-derived. The Indus-Yarlung ophiolites were thus emplaced and exposed to erosion since the Early Eocene (>50Ma) in the NW Himalaya, but only subsequently (50–38Ma) in the eastern Himalaya. [Copyright &y& Elsevier]

Abstract: Lower Cretaceous volcanic lithic arenites, widely distributed in the Tethyan Himalaya, provide insights into the continental breakup of Eastern Gondwana. In southern Tibet they are represented by the Wölong Volcaniclastics. The volcanic rocks that contributed clastic material to the lower parts of this unit were predominantly alkali basalts, whereas rhyolitic/dacitic volcanism becomes the predominant source of the upper strata. Geochemical analyses of basaltic grains and of detrital Cr-spinels from the Wölong Volcaniclastics demonstrate the alkaline character of the volcanism and suggest “within-plate” tectonic setting for the volcanism. Zircon U–Pb ages confirm that this volcanism continued from ∼140Ma to ∼119Ma. Hf-isotope data on these Early Cretaceous zircons indicate that their parental magmas were mantle-derived, but in the later stage of magmatic activity mantle-derived magmas were mixed with partial melts derived from the continental crust. The Lower Cretaceous volcaniclastics occur along a broad belt paralleling the northern margin of Greater India. The onset of volcaniclastic deposition in the Himalayas appears to become progressively younger toward the west, but it ended synchronously during the Late Albian (∼102Ma). The low volume of volcanic rocks and their intra-plate tectonic setting suggest that they are the result of decompressional melting along extensional deep-seated fractures cross-cutting the continental crust, and reflect changes in regional intra-plate tectonic stresses when Greater India began to separate from the Australia–Antarctica supercontinent. [Copyright &y& Elsevier]

• δ 34 S CAS shows a positive excursion around the Sinemurian–Pliensbachian boundary. • δ 34 S CAS shows a sharp negative–positive couplet in the upper Pliensbachian. SO 4 2 − declined during the Sinemurian to Toarcian reaching a minimum in the TOAE. • Obvious δ 34 S heterogeneity began in early Pliensbachian culminating in the T-OAE. The Early Jurassic is an important interval characterized by several global carbon-isotope (δ 13 C) perturbations. Although the δ 13 C records are becoming better documented during this time interval, we have a relatively poor understanding of the associated long-term environmental and climatic changes. In order to decipher these events, we here present new stable sulfur-isotope data of carbonate-associated sulfate (δ 34 S CAS) for the Sinemurian–Pliensbachian interval from the Wölong section in the Tibetan Himalaya that was located palaeogeographically in the southern hemisphere. An overall positive shift in δ 34 S CAS coincides with the negative δ 13 C excursion around the Sinemurian–Pliensbachian boundary, suggesting an increased 34S-depleted pyrite burial rate. The ensuing overarching negative δ 34 S CAS shift coincides with the upper Pliensbachian positive δ 13 C excursion. The initial falling limb of the δ 34 S CAS shift suggests a transient δ 34 S-depleted sulfate input, but this trend was soon reversed to become positive, likely caused by a persistently enhanced 32S-rich pyrite burial flux in the latest Pliensbachian. Modeling results show that maximum oceanic sulfate concentration likely decreased during the Sinemurian–Toarcian interval, probably due to large-scale evaporite deposition in the western Tethys and proto-Atlantic and enhanced pyrite burial in a number of marine settings. The concentration of seawater sulfate could have been high enough to maintain a homogeneous sulfur-isotope ocean in the late Sinemurian, but its persistent decrease may have initiated a spatially heterogeneous ocean after the Pliensbachian: an oceanic geochemical state that was amplified during the Toarcian Oceanic Anoxic Event. [ABSTRACT FROM AUTHOR]

Tourmaline is a borosilicate mineral commonly found in sedimentary rocks worldwide. It is chemically and mechanically stable and, as a host of boron in crustal rocks, it could be a useful indicator of rock sources. Despite this, its potential as a source indicator using the boron (B) isotope has remained largely under-explored. In this study, we propose a new integrated approach to fingerprint the origin of detrital tourmaline grains and test whether the approach is useful for identifying source rocks. Tourmaline grains in modern river sands from Southern Tibet were analyzed for optical properties, major elements, and B isotope composition. The geochemistry of detrital tourmaline in sand from the Nianchu and Pumchu rivers draining the Himalayan ranges is similar, and the B isotope values indicated they were mainly from Himalayan leucogranites. Tourmalines in the Lhasa River sand were derived from two major sources. Grains with high Al, low Mg, and strongly negative B isotope values (−12‰ to −16‰) were interpreted from the Gangdese arc batholith, whereas those with low Al, high Fe, and B isotope values of −2‰ to 2‰ were proposed most likely from Nyaingentanglha orthogneisses. We examined the relationships between tourmaline properties and found that B isotope values are useful as a source indicator. We also established a database of B isotope values for 2724 tourmaline crystals in different types of exposed rock spanning 37 countries, to promote the use of B isotope values in tourmaline in provenance studies. • Optical, geochemical, and B isotope features of tourmaline in sand were studied. • Tourmaline in the Nianchu and Pumchu derived from Himalayan leucogranite. • Tourmaline of Lhasa River derived from granite and orthogneiss in catchment. • Tourmaline B isotope should be coupled with geochemistry in provenance analysis. [ABSTRACT FROM AUTHOR]

Abstract: Lithostratigraphic studies of the Upper Jurassic–Lower Cretaceous sedimentary successions exposed in the Tingri–Gyangze area, south-eastern Tibet resulted in the establishment of a revised stratigraphic framework. A major crustal fault separates the southern Tibetan sedimentary successions into a Southern Zone and a Northern Zone. The Upper Jurassic–Lower Cretaceous strata of the Southern Zone are subdivided into the Menkadun Formation (Oxfordian, Kimmeridgian, up to lower Upper Tithonian), the Gucuo Formation (Upper Tithonian to Lower Albian) and the overlying Dongshan Formation (Upper Albian). The Gucuo Formation is further subdivided into a quartz arenite unit, which is overlain by a shale unit, in turn overlain by a volcaniclastic sandstone unit. The youngest cluster of detrital zircon absolute age data (127.7±1.8Ma) from the lower part of the volcaniclastic unit of the Gucuo Formation place the volcanic event before the Late Barremian. In the Northern Zone, the Upper Jurassic–Lower Cretaceous strata have been subdivided into four formations: the Zhera Formation (Upper Jurassic), the Weimei Formation (Tithonian), the Rilang Formation (?Berriasian) and the Gyabula Formation (? post-Valanginian). The appearance of silica cemented quartz arenites in both the quartz arenite unit of the Gucuo Formation and the Weimei Formation in the uppermost Jurassic is considered to provide strong evidence for an eustatic sea level drop affecting the northern margin of Greater India. In contrast the appearance of volcaniclastic sandstones in the Gucuo and Rilang formations are interpreted to represent a rift related volcanic event. The Menkadun–Zhera formations, the quartz arenite unit of the Gucuo Formation–Weimei Formation, the volcaniclastic sandstone unit–Rilang Formation in south-eastern Tibet are lithologically similar and broadly correlative with the Spiti Shale, Takh and Pingdon La formations in Zanskar (India), and Spiti Shale, Dangardzong, Kagbeni and Dzong formations in the Thakkhola area (Nepal). The onset of quartzose and subsequently volcaniclastic deposition becomes progressively younger westward, from the Gucuo region toward Zanskar. [Copyright &y& Elsevier]

Detrital geochronology, generally focused on zircon only, is widely used not only to obtain qualitative information on source areas but also in quantitative provenance analysis aimed at calculating sediment yields and erosion rates under the assumption that age spectra broadly reflect the proportions of areal exposures of source rocks. The principal aim of this article is to put this assumption to test. The Tibetan Plateau and Himalayan belt, in which the age of magmatic and metamorphic events has been accurately determined through decades of geological and geochronological studies, represent an excellent natural laboratory for provenance analysis. In this study, we focus on sand carried by three major Tibetan rivers - including the largest tributaries of the Yarlung Tsangpo draining either the Lhasa block or the Himalaya exclusively - and couple classical petrographic and heavy-mineral analyses with geochronological and geochemical fingerprinting of detrital zircon, monazite, titanite, and rutile as witnesses of episodes of crustal growth in their catchment. Zircon, rutile, monazite, and titanite provide different responses to magmatic and metamorphic events and are highly to moderately durable minerals that can be preserved in ancient sandstones, thus representing precious tracers in provenance analysis. Our results show that largely euhedral zircon and titanite grains in Lhasa River sand reflect the multiple magmatic events that affected the Lhasa block through the Mesozoic and Cenozoic, and together with detrital monazite and rutile highlight post-collisional metamorphic events in the Nyainqentanglha Range. Mostly rounded detrital minerals generated in the Nianchu and Pumchu catchments are instead largely recycled from Tethys Himalayan sedimentary rocks, but young ages of monazite and titanite grains reflect the widespread Miocene thermal event associated with leucogranite intrusions both at the top of the Greater Himalayan metamorphic unit and in Northern Himalayan gneiss domes. The geochemical signature of most rutile grains in all studied samples indicates ultimate provenance from metapelites. Most important, the age spectra of different datable detrital minerals reflect poorly and in very different proportions the areal exposure of source-rock lithologies (and in the Lhasa River catchment also the areal exposure of granitoids of different age). We conclude that, although detrital geochronology does provide essential information in qualitative provenance reconstructions, the age distributions of single minerals cannot be reliably converted in terms of proportional sediment yield, and thus cannot be used to calculate sediment budgets or trace erosion rates unless fertility bias is accurately quantified and taken into due account. [ABSTRACT FROM AUTHOR]