Search

Whether tectonic strain from the early stage India‐Asia collision has synchronously affected the far‐field margin of the Tibetan Plateau is crucial for understanding plateau deformation and growth processes. However, direct evidence for early far‐field deformation remains scarce. Utilizing illite K‐Ar dating of three fault gouge samples, we established the faulting history of the Leibo fault zone (LFZ) at the southeastern margin of the Tibetan Plateau (SEMTP). Consistent authigenic illite ages of 52 ± 2, 54 ± 12 and 55 ± 6 Ma suggest the reactivated thrust faulting of the LFZ in the Early Cenozoic. Positioned ∼700 km east of the collisional boundary and at the intersection of three blocks with distinct lithospheric rheology in strength/viscosity, this event suggests a quasi‐synchronous far‐field tectonic response in the SEMTP to the India‐Asia collision. Plain Language Summary: Understanding how tectonic strain resulting from the collision between the Indian and Eurasian plates in the Early Cenozoic can spread to the edges of the Tibetan Plateau is crucial for comprehending the plateau's tectonic development. To investigate this question, we used fault gouge, which resulted from the sliding of brittle faults, to directly reveal faulting information. By conducting illite K‐Ar dating on three samples from the Leibo fault zone (LFZ) at the southeastern margin of the Tibetan Plateau (SEMTP), we found consistent ages of newly formed illite, 52 ± 2, 54 ± 12, and 55 ± 6 million years ago. Since this type of minerals form simultaneously with faulting, these ages reveal a reactivated thrust faulting event of the LFZ, suggesting a nearly simultaneous response of faulting in the SEMTP to the early stage of the India‐Asia collision. Key Points: Fault gouge illite K‐Ar dating is used to establish the faulting history of the Leibo fault zone, SE margin of the Tibetan PlateauThree consistent authigenic illite ages of ∼55, ∼54, and ∼52 Ma suggest a reactivated thrust faulting event of the Leibo fault zoneThis event indicates a quasi‐synchronous far‐field response of the SE margin of the Tibetan Plateau to the India‐Asia collision [ABSTRACT FROM AUTHOR]

Long‐distance lateral magma propagation may reflect the complex interaction between regional tectonics and crustal uplift. Here, we report observations on the Taxkorgan intrusive complex (TIC) of the Central Pamir. TIC is a 70 km long, 10–18 km wide, north‐northwest–elongated body intruded into mid‐upper crust in parallel with, and close to, the Kongur Shan Extensional System. New zircon U‐Pb dating shows that syenite samples exhibit a clear younging pattern from south to north along the pluton axis within an interval between 11.5 and 10.3 Ma, which is interpreted as lateral magma propagation from a single feeder zone at its northwestern margin. The lateral magma propagation was caused by a combination of crustal rigidity differences, and a topography‐induced pressure gradient that is nearly orthogonal to the least compressive stress. We propose that long‐distance lateral magma propagation plays an important role in plateau expansion, restraining the thickness and elevation of the Pamir Plateau. Plain Language Summary: Long‐distance lateral magma propagation within the crust has been documented for diverse magmatic systems. The Miocene Taxkorgan intrusive complex was formed during India‐Asia collision in the Central Pamir Plateau, and it consists of a syenite pluton and several discrete lobes of monzogranites. New SIMS zircon U‐Pb dating results shows that monzogranites across TIC have overlapping ages between 12.4 and 12.2 Ma, indicating they were emplaced from a series of synchronous and independent magma feeder zones. In contrast, syenite samples exhibit a clear younging pattern from south to north within an interval between 11.5 and 10.3 Ma. The pattern of decreasing ages along the pluton axis is interpreted as lateral magma propagation from a single feeder zone at its northwestern margin. It is inferred that long‐distance lateral magma propagation, such as documented for the Taxkorgan intrusive complex, played a key role in plateau expansion, restraining the thickness and elevation of the Pamir Plateau. Key Points: Taxkorgan intrusive complex (TIC) syenite pluton shows a clear younging pattern from south to north within an interval between 11.5 and 10.3 MaTIC syenite pluton formed by lateral magma propagation from a single feeder zone at its northwestern marginLong‐distance lateral magma propagation plays an important role in plateau expansion, restraining the thickness and elevation of Plateau [ABSTRACT FROM AUTHOR]

Paleocene lavas of the Dianzhong Formation preserved in the Linzhou Basin of South Tibet provide a unique opportunity to constrain the initial geometry of the India‐Asia collision; however, earlier studies argued a complex magnetic signature resulting from thermal and/or chemical remagnetizations. To better characterize the remanences obtained from the Dianzhong lavas, we carried out an intraformational conglomerate test on a previously‐studied section in the Linzhou Basin. The positive conglomerate test suggests that the characteristic remanences reported from the Dianzhong Formation are primary. The updated Paleocene pole confirms a paleolatitude of 6.7° ± 4.4°N for the Lhasa terrane and positions the southern margin of Asia in the equatorial humid belt. An initial collision, between India, Asia and an intra‐oceanic arc in the equatorial humid belt, may have intensified silicate weathering and resulted in an extra consummation of carbon dioxide, which contributes to a long‐term cooling of the Earth during the Cenozoic. Plain Language Summary: The locus of the initial India‐Asia collision can be constrained using paleomagnetic studies on the Paleocene volcanics from the Linzhou Basin, South Tibet. However, the primary nature of the magnetic signature previously reported from the Dianzhong Formation was questioned. This study carries out an intraformational conglomerate test collected from the middle part of the Dianzhong Formation. The stable remanences isolated from a layer of intercalated lava cobbles yield a random distribution in contrast to the well‐grouped directions obtained from the over‐ and underlying lava layers resulting in a positive conglomerate test. We therefore argue for a primary nature for the characteristic remanence recorded by the Dianzhong lavas from the Linzhou Basin. Our study confirms a low latitude of ∼7°N, that is, within the equatorial humid belt, for the southern margin of Asia during ∼64–60 Ma. An initial low‐latitude collision between India and Asia is critical for understanding the tectonic and climatic significance of the India‐Asia collision. Key Points: Characteristic remanences reported from the Dianzhong lavas in the Linzhou Basin are primary in originThe updated Paleocene pole confirms a low latitude of ∼7°N for the Lhasa terraneAn initial collision between India, Asia and an oceanic arc in the equatorial humid belt may contribute to the Cenozoic cooling of the Earth [ABSTRACT FROM AUTHOR]

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 onsetThe India‐Asia provenance reversal is bracketed between 62.7 and 61 Ma in the Mubala sectionSubduction of the Indian continental margin beneath Asia began by 61 Ma [ABSTRACT FROM AUTHOR]

When and how the TP underwent uplift and deformation are still under heated debate. We present paleomagnetic evidence for the NB in the northeastern central TP to help decipher the potential plateau deformation mechanism. Magnetostratigraphy with zircon U‐Pb age of volcanic rock demonstrates that the NB basin deposited during 52.5–35.0 Ma. Paleomagnetic declinations indicate that the basin experienced counterclockwise rotation of 25.9 ± 7.2° during 52–46 Ma and clockwise rotation of 24.4 ± 9.7° during 41–35 Ma, which coexisted with the intrusion and explosion of volcanic rocks at 51–46 and 39–35 Ma. We proposed a stepwise compression and extrusion model to interpret the basin deposition, rotation, and volcanism by northward compression and eastward extrusion of the eastern Lhasa and Qiangtang Blocks (Proto‐TP) in relation to the Sichuan Basin as early response to the India‐Asia collision. Plain Language Summary: How the Tibetan Plateau (TP) adjusted its inner crustal thickening and tectonic deformation during the India‐Asia collision is still in hot debate, for example, through lateral extrusion or continuous distribution. The Nangqian Basin (NB) is located in the bending (transitional) part from an east‐west tectonic area in the central TP to a north‐south tectonic area in the eastern and southeastern TP. It is an ideal location to provide abundant tectonic evidences for the plateau deformation and uplift models. We report a detailed paleomagnetic dating of the Paleogene sedimentary sequence from the NB with a complete paleomagnetic rotation analysis. Radiometric and magnetostratigraphic dating suggested that the NB commenced its deposition at 52.5 Ma and ended at 35.0 Ma. Paleomagnetic declination data reveal a change of rotation sense of the NB, from a counterclockwise rotation of 25.9° at 52–46 Ma to a clockwise rotation of 24.4° at 41–35 Ma. Integrated with other lines of geological evidence, we believe that the Eocene deformation, rotation, and uplift of the south and east central TP in response to the early India‐Asia collision can be explained by stepwise compressions and eastward extrusions. Key Points: Magnetostratigraphic results demonstrate that the Early Cenozoic sedimentary sequence of the Nangqian Basin yields ages of 52.5–35.0 MaDeclination data indicate change of rotation in the Nangqian Basin from counterclockwise during 52–46 Ma to clockwise during 41–35 MaThe Eocene deformation, rotation, and uplift of the east central Tibetan Plateau favor the compression and extrusion model [ABSTRACT FROM AUTHOR]