The 87Sr/86Sr Record of Himalayan Paleorivers During the Neogene: Patterns and Causes

点击翻译按钮获取中文摘要

9725607 Quade The Himalayas stand at the center of the debate on how mountain building can alter climate. One of the clearest proxies of the global effects of Himalayan uplift is the marine 87Sr/86Sr record. Yet the specific contribution that past and present Himalayan rivers make to the marine 87Sr/86Sr record, and how this contribution translates quantitatively into silicate weathering rates and therefore consumption of atmospheric CO2 is unclear. Our recent research demonstrates that the 87Sr/86Sr ratios of Himalayan paleorivers can be reconstructed from carbonates preserved in the Siwalik Group foreland basin deposits in the frontal part of the Himalayan fold-thrust belt. These data show 87Sr/86Sr ratios have increased markedly in the late Neogene, probably in response to unroofing of high 87Sr/86Sr (0.720-0.729) marble and dolostone in the Lesser Himalayan and frontal Himalayan nappes. We propose to (1) expand our Himalayan river 87Sr/86Sr record into easternmost Nepal, and back to the beginning of the Miocene, thereby completing the isotopic history for the paleo-Ganges river system, (2) quantify the contribution of carbonate versus silicate weathering in a modern Nepali river, and (3) combine the isotopic data with sedimentological, structural, and provenance data from the foreland basin deposits in order to document the entire record of erosional unroofing of the Nepal Himalayas since the beginning of the Miocene. The results of the proposed research will have major implications for our understanding of the relationships between collisional orogenesis, climate, and ocean water chemistry.