One Year Renewal Request: Investigation of Syncollisional Extension and Basin Development in the High Himalaya

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Initial Indo-Asian intercontinental collision is considered to have begun approximately 55 million years ago along the Indus suture zone. This work is focused on a thick succession of Cenozoic clastic sediments that accumulated along the suture zone and recorded the evolution of flanking source terranes, depositional environments, and regional paleoelevation. The Kailas Formation consists of thick alluvial fan to lacustrine deposits that were derived mainly from the north side of the suture zone. U-Pb zircon ages from interbedded tuffs indicate an age of 26 to 23 million years ago, roughly 20 to 30 miliion years younger than previously documented in the literature. As such, the Kailas Formation no longer can be interpreted as the result of intercontinental collision during Eocene time. Moreover, sedimentological and paleobotanical data demonstrate deposition in large deep lakes, which preserved abundant algal and terrestrial plant material and vertebrate fossils. Palynological data suggest humid tropical pollen assemblages, and raise the prospect that the Kailas lakes formed at moderate to low elevation, fully 30 million years after the putative onset of collision. Today these rocks crop out at elevations above 6,000 meters, demonstrating that attainment of high regional elevation in southwestern Tibet was much later than previously assumed. Previous research in central Tibet on rocks of identical age to the Kailas Formation showed high elevations in that region by late Oligocene. Therefore, central Tibet had already become very high by the time that the Kailas Formation was accumulating at apparently much lower elevation along the suture zone. Together this research provides new insights but also raises many questions about the timing and nature of the initial collision, the mechanics of development of the Tibetan Plateau, and its implications for changing ocean chemistry and paleoclimate dynamics. This project is focused on the geological history of the complex zone that marks the site of collision between the Indian and Asian continents. This collision began perhaps as early as 55 million years ago and has produced the largest mountain range on Earth - the Himalayan-Tibetan orogen. The Himalayan mountains are higher than 8,000 meters and the Tibetan Plateau has an average elevation over an area equivalent to the western third of the United States that is higher than the tallest mountain in the conterminous United States. This colossal orogenic system has a profound effect on global climate dynamics and ocean chemistry, but understanding of how and when the system developed is poor. This project is designed to shed light on the timing of the Indo-Asian collision by gathering data from sedimentary rocks that were deposited right along the collision zone, or suture zone. The results of this study would challenge the idea that the collision began as early as 55 million years ago and, thus, would have major implications for the mechanics of the entire collision process as well as impact scientific understanding of Cenozoic ocean and climate evolution. The work is being conducted in collaboration with Drs. Ding Lin and Zhang Haijun and several graduate students from the Institute of Tibetan Plateau Research, Chinese Academy of Sciences, Beijing.