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

9725607 Quade喜马拉雅山站在了造山如何改变气候的争论的中心。海洋87Sr/86Sr记录是喜马拉雅隆起对全球影响最清晰的代用物之一。然而，过去和现在的喜马拉雅河流对海洋87Sr/86Sr记录的具体贡献，以及这种贡献如何定量地转化为硅酸盐风化速率，从而转化为大气二氧化碳的消耗，目前还不清楚。最近的研究表明，喜马拉雅褶皱冲断带前缘Siwalik群前陆盆地沉积中保存的碳酸盐岩可以重建喜马拉雅古河流的87Sr/86Sr比值。这些数据表明，87Sr/86Sr比值在新近纪晚期显著增加，可能是由于喜马拉雅小推覆体和喜马拉雅前缘推覆体的高87Sr/86Sr（0.720-0.729）大理岩和白云岩的剥落所致。我们建议(1)将喜马拉雅河87Sr/86Sr记录扩展到尼泊尔最东部，并追溯到中新世开始，从而完成古恒河系统的同位素历史；(2)量化碳酸盐岩和硅酸盐风化在现代尼泊尔河流中的贡献；(3)将同位素数据与沉积学、构造学、以及来自前陆盆地沉积物的物源数据，以便记录中新世以来尼泊尔喜马拉雅山脉侵蚀剥落的全部记录。所提出的研究结果将对我们理解碰撞造山作用、气候和海水化学之间的关系产生重大影响。

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.