discovery of upper cretaceous neo tethyan trench deposits in south tibet luogangcuo formation

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Late Cretaceous to Late Eocene Exhumation in the Nima Area, Central Tibet:Implications for Development of Low Relief Topography of the Tibetan Plateau

Much of the interior of the Tibetan Plateau is characterized by internal drainage, low relief topography, and high altitude. How and when this landscape formed is controversial. In this study, we use new zircon U-Pb data and low-temperature thermochronological data (apatite and zircon [U-Th/He], apatite fission track [AFT]) from the Late Cretaceous to Cenozoic Nima Basin sedimentary rocks and Xiabie granite in the adjacent Muggar Thrust hanging wall (part of the regional Shiquanhe-Gaize-Amdo thrust system), to determine the paleodrainage and timing of exhumation in the region. Individual AHe and ZHe cooling ages range from 9 to 60 Ma and 58 to 118 Ma, and the AFT ages range from 30 to 90 Ma. The thermal history derived from the Northern Nima Basin sediments and Xiabie granite require a period of exhumation between 70 and 40 Ma in the thrust fault hanging wall, and 40 and 30 Ma in the Nima Basin. Across the region, this event was followed by low rates of exhumation and the deposition of locally sourced sediment, lacustrine, and evaporitic deposits that are indicative of an internal drainage system. We suggest that the exhumation event is associated with development of thrust-elevated relief that may have disrupted the drainage network favoring the development of an endorheic system. This system, sediment accumulation, and/or post-30 Ma tectonic quiescence led to the generation of low relief topography

Carbonate-platform response to the Toarcian Oceanic Anoxic Event in the southern hemisphere : Implications for climatic change and biotic platform demise

We are grateful to Zhifei Liu for TOC and analyses at the Tongji University. We thank also Wei An, Bo Zhou and Shiyi Li for their assistance in the field, and Zhicheng Huang, Yiwei Xu and Weiwei Xue for their help in the laboratory, and Chao Chang, Tianchen He and Bolin Zhang for their helpful discussion. Hugh Jenkyns commented on a draft of the manuscript. We would also like to thank Editor Derek Vance, Christopher Pearce and two anonymous reviewers whose comments greatly improved the manuscript. This study was financially supported by the National Natural Science Funds for Distinguished Young Scholar in China (41525007) and the Chinese MOST 973 Project (2012CB822001). DBK acknowledges support of NERC Fellowship NE/I02089X/1. This is a contribution to the IGCP 655.Peer reviewedPostprin

Late Paleozoic magmatism in South China : oceanic subduction or intracontinental orogeny?

A gneissic granite with an U-Pb age of 313±4 Ma was found in northeastern Fujian Province, South China. It is an S-type granite characterized by high K₂O, Al₂O₃ and low SiO₂, Na₂O contents with high A/CNK ratio of 1. 22 for the whole rock. Zircons with stubby morphology from the gneissic granite yield ²⁰⁶Pb/²³⁸U ages ranging from 326 to 301 Ma with a weighted average age of 313±4 Ma, and negative ℇHf(t) values from -8. 35 to -1. 74 with Hf model ages (TC DM) of 1. 43 to 1. 84 Ga. This S-type granite probably originated from late Paleoproterozoic crust in intracontinental orogeny. Integrated with previous results on paleogeographic reconstruction of South China, the nature of Paleozoic basins, Early Permian volcanism and U-Pb-Hf isotope of detrital zircons from the late Paleozoic to early Mesozoic sedimentary rocks, we suggest the occurrence of a late Paleozoic orogeny in the eastern Cathaysia Block, South China. This orogenic cycle includes Late Carboniferous (340-310 Ma) orogeny (compression) episode and Early Permian (287-270 Ma) post-orogenic or intraplate extension episode. Therefore, the late Paleozoic magmatism in the southeastern South China probably occurred during the intraplate orogeny rather than the arc-related process.8 page(s

Late Cretaceous-Eocene exhumation of the northern Lhasa terrane and topographic implications for the Central Tibet

The central Tibetan Plateau has an average altitude of ~5000 m; its exhumation and chemical weathering greatly influence the global climate and ocean chemistry. The modern central Tibet is characterized by low-relief, high elevation topography with endorheic drainage. When and how these geomorphic characteristics of central Tibet were initiated remains controversial. Here, we have applied zircon Usingle bondPb dating and low-temperature thermochronology on the Cretaceous plutons from Coqin Basin of central Tibet in order to assess timings of exhumation. The thermal history modeling indicates a period of relatively rapid cooling (2.5–4 °C/Ma) occurred in Late Cretaceous to Middle Eocene times (from ~80 Ma to ~40 Ma), with the exhumation rates of 0.2–0.4 mm/yr assuming a geothermal gradient of 25 °C/km. Cooling rates then slowed to ~0.5 °C/Ma during the Middle Eocene to the present, with a relatively lower exhumation rates of ~0.02–0.03 mm/yr. Synchronous rapid cooling and exhumation has also been identified in central Tibet; this signal of widespread Late Cretaceous exhumation across the region may be viewed as evidence for the initial surface uplift and erosion of the central Tibetan plateau. Lower exhumation rate since ~40 Ma, combined with sedimentological data suggests that the low-relief, internally drained topography of central Tibet was initiated around this time