The timing of initial collision between India and Asia has remained controversial for half a century. This paper attempts to review this crucial and hotly debated argument, describing first the ...different methods used to constrain the age of collision and discussing next the rationale, results, inferences and problems associated with each. We conclude that stratigraphy represents the best direct way to unravel collision chronology. Other methods focusing on the magmatic, metamorphic or paleomagnetic record provide additional fundamental constraints, but cannot provide a robust direct estimate of collision onset.
Initial collision in the central-eastern Himalaya is dated directly at the middle Paleocene (59±1Ma) by the abrupt change in sediment provenance recorded in trench settings. The quasi-synchronous unconformities documented along both Tethyan passive margin of India and active margin of Asia from Tibet to Zanskar-Ladakh confirm that orogeny was underway at the close of the Paleocene (56Ma), well before the disappearance of marine seaways in the Himalaya during the early-middle Eocene (50–45Ma). Sedimentary evolution and provenance changes in marine to fluvio-deltaic successions are recorded synchronously within error from the western to the central-eastern Himalaya, failing to provide conclusive evidence for diachronous collision.
These coherent observations are hard to reconcile with three widely cited hypotheses invoking either Paleogene arc-continent collision or Late Cretaceous ophiolite obduction, or the protracted existence of a Greater India Basin, which are all not favored after discussing the geological evidence critically point by point. A scenario no more complex than the one involving solely the passive continental margin of India and the active continental margin of Asia is needed to explain the geological evolution of the nascent Himalaya. The collision between the Tethys Himalaya and the Transhimalayan arc-trench system does represent the collision between India and Asia. Because the Yarlung Zangbo Ophiolite is the forearc basement of the Asian active margin, its obduction onto India could not have preceded the initial closure of Neo-Tethys. Ophiolite obduction began when collision began, in the middle Paleocene.
A deeper understanding of hyperthermal events in the Earth’s history can provide an important scientific basis for understanding and coping with global warming in the Anthropocene. Two types of ...hyperthermal events are classified based on the characteristics of the carbon isotope excursion (CIE) of the five representative hyperthermal events in the Mesozoic and Cenozoic. The first type is overall characterized by negative CIEs (NCHE) and represented by the Permian-Triassic boundary event (PTB, ~252 Ma), the early Toarcian oceanic anoxic event (TOAE, ~183 Ma), and the Paleocene-Eocene Thermal Maximum event (PETM, ~56 Ma). The second type is overall characterized by positive CIEs (PCHE) and represented by the early Aptian oceanic anoxic event (OAE1a, ~120 Ma) and the latest Cenomanian oceanic anoxic event (OAE2, ~94 Ma). Hyperthermal events of negative CIEs (NCHE), lead to dramatic changes in temperature, sedimentation, and biodiversity. These events caused frequent occurrence of terrestrial wildfires, extreme droughts, acid rain, destruction of ozone layer, metal poisoning (such as mercury), changes in terrestrial water system, and carbonate platform demise, ocean acidification, ocean anoxia in marine settings, and various degree extinction of terrestrial and marine life, especially in shallow marine. In contrast, hyperthermal events of positive CIEs (PCHE), result in rapid warming of seawater and widespread oceanic anoxia, large-scale burial of organic matter and associated black shale deposition, which exerted more significant impacts on deep-water marine life, but little impacts on shallow sea and terrestrial life. While PCHEs were triggered by volcanism associated with LIPs in deep-sea environment, the released heat and nutrient were buffered by seawater due to their eruption in the deep sea, thus exerted more significant impacts on deep-marine biota than on shallow marine and terrestrial biota. This work enriches the study of hyperthermal events in geological history, not only for the understanding of hyperthermal events themselves, large igneous provinces, marine and terrestrial environment changes, mass extinctions, but also for providing a new method to identify the types of hyperthermal events and the inference of their driving mechanism based on the characteristics of carbon isotopic excursions and geological records.
The Xiukang Mélange of the Yarlung-Zangbo suture zone in south Tibet documents low efficiency of accretion along the southern active margin of Asia during Cretaceous Neotethyan subduction, followed ...by final development during the early Paleogene stages of the India–Asia collision. Here we present integrated petrologic, U–Pb detrital-zircon geochronology and Hf isotope data on different types of sandstone blocks in the Xiukang Mélange. Three groups of sandstone blocks with different provenance and depositional setting are distinguished by their petrographic, geochronological and isotopic fingerprints. Blocks of turbiditic quartzarenite originally sourced from the Indian continent were deposited in pre-Cretaceous time on the northernmost edge of the Indian passive margin and eventually involved into the mélange at the early stage of the India–Asia collision. Two distinct groups of volcaniclastic-sandstone blocks were derived from the central Lhasa block and Gangdese magmatic arc. One group was deposited in the trench and/or on the trench slope of the Asian margin during the early Late Cretaceous, and the other group in a syn-collisional basin just after the onset of the India–Asia collision in the Early Eocene. The largely erosional character of the Asian active margin in the Late Cretaceous is indicated by the scarcity of off-scraped trench-fill deposits and the relatively small subduction complex developed during limited episodes of accretion. The Xiukang Mélange was finally structured in the Late Paleocene/Eocene, when sandstone blocks of both Indian and Asian origin were progressively incorporated tectonically in the suture zone of the nascent Himalayan Orogen.
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•Xiukang Mélange contains sandstone blocks derived from both India and Lhasa terrane.•Xiukang Mélange evolved during both Cretaceous subduction and Paleocene collision.•Asian active margin was largely erosional but partly accretional in Late Cretaceous.
Diverging interpretations and incompatible scenarios have been proposed for the early stages of Himalayan history. Numerous researchers have postulated that northern India was involved in ophiolite ...obduction, arc–continent, or continent–continent collision during the Late Cretaceous or Early Paleocene, but firm geological evidence was never produced. In this article we argue against orogenic events predating the Late Paleocene, when the Neotethys Ocean was still open. The Tethys Himalayan sedimentary record testifies to anorogenic evolution, primarily controlled by dynamic uplift of the passive margin prior to the massive outburst of Deccan lavas and eventually followed by thermal subsidence. Major stratigraphic gaps in pelagic sediments suggest that such tectono-magmatic episode started to affect the base of the Indian Plate in the Campanian or possibly even in the Santonian, 10 to 20Ma before the climax of Deccan flood-basalt eruptions. The abrupt increase in siliciclastic supply and accumulation rates recorded in sedimentary basins all around the Indian subcontinent during the Maastrichtian was followed by progradation of coastal quartzarenites along the northern Indian margin in the Early Paleocene. Sandstones derived from the rejuvenated craton and uplifted inner continental margin in the south are dominantly but not exclusively quartzose. Felsitic volcanic rock fragments and Cr-spinels, many of which with the same geochemical fingerprint as Deccan spinels and newly found throughout the Maastrichtian to Danian succession, resisted the combined effect of subequatorial weathering and subsequent diagenesis, and testify that detritus from Deccan basalts reached the Indian passive margin as far as South Tibet. At the close of the Early Paleocene India drifted away from the Seychelles block, and thermal subsidence led to widespread carbonate deposition along the Tethys Himalaya. This article illustrates how mega-events of magmatic upwelling followed by lithospheric cooling may control passive-margin sedimentation and stratigraphic patterns, as occurred in northern India first in the Early Cretaceous and next in the latest Cretaceous/Paleocene.
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•Sedimentary record rules out the onset of India–Asia collision in the Late Cretaceous.•Forearc basement was not obducted onto India before Paleocene/Eocene collision.•Same Cr-spinel chemistry in Tethys Himalayan sandstones and Deccan flood basalts.•Uplift and erosion of India were driven by magmatic upwelling in the Maastrichtian.•Passive-margin stratigraphy records tectono-magmatic events followed by cooling.
The stratigraphic succession of a forearc basin provides crucial information on the history of a convergent plate margin. In particular, it helps to establish the origin of the underlying ophiolites ...and to unravel the earliest evolutionary stage of arc-trench systems, which remain poorly understood. The Xigaze forearc basin in southern Tibet is one of the best examples of a fossil forearc basin. This study illustrates detailed stratigraphic and high-precision SIMS U–Pb zircon geochronological and Hf isotopic data from the Chongdui Formation, representing the very base of the Xigaze forearc-basin succession, and reconstructs when and how the basin was formed. The Chongdui Formation includes tuffaceous chert and siliceous mudrocks deposited directly on top of pillow basalts of the Xigaze ophiolite and conformably overlain by volcaniclastic turbidites. Tuff layers are interbedded throughout the unit, and their U–Pb zircon ages range from 119 to 113 Ma in the lower member and from 113 to 110 Ma in the upper member, broadly consistent with the established radiolarian biostratigraphy. U–Pb ages and Hf isotope signatures of zircons contained in both tuff layers and turbiditic sandstones indicate clear affinity with magmatic rocks of the Lhasa terrane. Direct depositional and chronostratigraphic relationship with the underlying oceanic crust, dated between 131 and 124 Ma, proves that the Xigaze ophiolite is the basement of the Xigaze forearc basin. After an initial prolonged stage of starved siliceous sedimentation, influx of terrigenous detritus began at 113–110 Ma, reflecting the onset of topographic growth and erosion of the Lhasa terrane in response to intense magmatic activity. Formation of the ophiolitic basement during the early stage of subduction and the subsequent topographic growth of the arc source induced by subduction-related magmatism are thus two critical factors for the birth of the Xigaze forearc basin. Similar stratigraphies were identified in the Great Valley and Luzon Central Valley forearc basins, suggesting that the initial geodynamic evolution of the Xigaze forearc basin may be common to many other forearc basins worldwide.
•The Xigaze forearc basin was built above the newly formed Xigaze ophiolites.•Stratigraphic base comprises a lower siliceous member and an upper turbidite member.•Siliceous deposition with Transhimlayan tuffs followed the formation of ophiolites.•Deposition of volcaniclastic turbidites began at 113–110 Ma.•Early stages of Neotethyan subduction determined the birth of Xigaze forearc basin.
The Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Ma) was a profound short-term environmental perturbation associated with the large-scale release of 13C-depleted carbon into the global ocean–atmosphere ...system, which resulted in a significant negative carbon-isotope excursion (CIE). The general lack of characteristic T-OAE records outside of the northern hemisphere means that the precise environmental effects and significance of this event are uncertain. Many biotic carbonate platforms of the northern hemisphere western Tethys drowned or shifted to non-skeletal platforms during the early Toarcian. However, southern hemisphere records of Toarcian carbonate platforms are rare, and thus the extent and significance of biotic platform demise during the T-OAE is unclear. Here we present high-resolution geochemical and sedimentological data across two Pliensbachian–Toarcian shallow-water carbonate-platform sections exposed in the Tibetan Himalaya. These sections were located paleogeographically on the open southeastern tropical Tethyan margin in the southern hemisphere. The T-OAE in the Tibetan Himalaya is marked by a negative CIE in organic matter. Our sedimentological analysis of the two sections reveals an abundance of storm deposits within the T-OAE interval, which emphasizes a close link between warming and tropical storms during the T-OAE event, in line with evidence recently provided from western Tethyan sections of the northern hemisphere. In addition, our analysis also reveals extensive biotic carbonate-platform demise by drowning or changing to non-skeletal carbonates coincident with the onset of the CIE. Taken together, our results suggest that rapid and pervasive seawater warming in response to carbon release likely played a significant role in sudden biotic carbonate platform demise, and suppression/postponement of biotic platform re-development along the whole tropical/subtropical Tethyan margin.
•The T-OAE is recognized on the shallow carbonate platform in southern hemisphere.•Increased storm deposits point to climatic disturbance related to warming.•Warmth likely led to the sudden biotic platform demise and delayed their redevelopment.
The timing of the India‐Asia collision onset, essential to understanding the evolution of the Himalayan‐Tibetan orogen, has been widely investigated through multidisciplinary approaches. Among these, ...the India to Asia provenance reversal (IAPR) documented in the Indian passive margin successions has proved to be most effective. We present integrated stratigraphic, sedimentological, and provenance data on Upper Cretaceous‐Paleogene strata from the newly investigated Mubala section exposed south of the Yarlung‐Zangbo suture zone (YZSZ) in southern Tibet, which preserves continuous deep‐marine turbiditic and biogenic sedimentation on the distal Indian passive margin. Sandstone petrography, heavy minerals, detrital zircon geochronology and Hf isotopes, and detrital Cr‐spinel geochemistry constrain the IAPR to later than 62.7 Ma (youngest zircon ages from the earliest Asian‐derived sandstone) and by 61.0 ± 0.3 Ma (SIMS age of a tuffaceous layer ∼30 m above this bed). The onset of intercontinental collision along the YZSZ began by 61 Ma.
Plain Language Summary
The India‐Asia collision, ultimately leading to uplift of the Himalayan Mountains and Tibetan Plateau, has greatly influenced global climate and oceanic circulation. The timing of collision is essential to reconstruct the growth history of the Himalayan‐Tibetan orogen and its environmental and paleogeographic effects. The change in sediment provenance documented along the Indian continental margin has proved to be a most effective method to constrain the timing of initial collision. We here report a newly‐discovered sedimentary succession deposited onto the deep‐marine edge of India, in which strata composed of detritus derived entirely from India are overlain by strata composed of detritus derived instead from Asia. This provenance change took place later than 62.7 million years ago (Ma; which is the age of the youngest group of zircons contained in the oldest sandstone derived from Asia) and 61.0 ± 0.3 Ma (which is the age of zircon crystals contained in a volcanic tuff found 30 m above the oldest Asian‐derived sandstone). The Indian and Asian continents thus first came into direct contact by 61 Ma.
Key Points
Sandstones derived first from India and next from Asia constrain India‐Asia collision onset
The India‐Asia provenance reversal is bracketed between 62.7 and 61 Ma in the Mubala section
Subduction of the Indian continental margin beneath Asia began by 61 Ma
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