Collaborative Research: Exhumation History of the Indian Lesser Himalaya: Discriminating Tectonic Models with Implications for the Neogene Isotopic Composition of Seawater

印度板块和欧亚板块碰撞导致喜马拉雅山脉隆起，这是板块构造学中大陆碰撞的典型例子。造山带的隆升对地表系统过程和岩石圈动力学的影响是巨大而深远的。该项目将采用综合多学科方法，更好地了解印度小喜马拉雅“外”喜马拉雅地区逆冲断层变形和地壳岩石挖掘的时间和顺序。这项研究将大大提高我们对与造山有关的挤压驱动的地壳变形过程的理解。这些结果将为批判性地评估季风强度与逆冲断层传播之间的潜在关系提供一种手段，并记录喜马拉雅隆起、挖掘和化学风化对海洋化学的重要性。沉积岩石中锇同位素比值（187Os/188Os）已被用作全球化学风化的代用物，本研究结果将为未来的全球海洋学和气候模式提供具有深远影响的数据。除了本研究的科学目标之外，对社会和国家利益的潜在好处还包括：为大型研究机构的早期职业研究人员提供支持；科学、技术、工程和数学（STEM）学科的研究生和本科生培训；一名美国研究生和博士后研究员与印度科学家进行国际合作；针对美国和印度K-12学生的教育和推广活动；以及为公众开发基于网络的信息贡献。该项目将促进代表性不足的群体扩大对科学的参与，工作成果将通过专业科学报告、同行评议的科学文献传播研究成果，并将研究成果纳入向公众开放的社区数据库。该项目包括对印度北部喜马拉雅锋面系统的基岩和前陆盆地沉积物进行高分辨率地质/热年代学调查，以限制小喜马拉雅不同区域的挖掘时间。这项工作将集中在主要逆冲片上的一系列走向垂直横断面上，对锆石和磷灰石进行（铀-钍）/氦定年，并通过对前陆盆地矿床进行详细的相分析和锆石铀-铅-氦（U-Pb-He）双定年进行物源研究。对小喜马拉雅断块的逆冲扩展序列，特别是“外”小喜马拉雅带的发掘时间和构造亲和性提出了对比模型。这些模型假定“外部”小喜马拉雅地带的构造就位年龄从始新世晚期到不到1400万年前——可能存在1400万年到3000万年的差异。然而，最近对前陆盆地物源数据的研究表明，“外部”小喜马拉雅带可能是在大约16 Ma时被挖掘出来的，这与季风强度的显著增加相对应。“外”小喜马拉雅带岩石富含放射性成因1870 - o的风化作用与1600万年前新近纪海水1870 - o / 1880 - o的显著增加有关。我们的综合研究将限制“外”小喜马拉雅带的冲断传播序列和挖掘时间，使我们能够：1)区分喜马拉雅冲断带演化的对比运动学模型，2)验证喜马拉雅不同构造带的挖掘和风化是新近纪海水化学长期变化的主要驱动因素的假设。初步的(U-Th)/He年代学数据为喜马拉雅风化与海水化学之间的直接联系的假设提供了有趣的支持。该奖项由美国国家科学基金会国际科学与工程部共同资助。

The uplift of the Himalayan Mountains due to collision of the Indian and Eurasian plates is the textbook example of continental collision in plate tectonics. The effect that uplift of this orogenic belt has had on the Earth surface system processes and lithospheric dynamics has been dramatic and far-reaching. This project will use an integrative multidisciplinary approach to better understand timing and sequence of thrust fault deformation and exhumation of crustal rocks in the 'outer' Himalayan zone of the Lesser Himalaya of India. The research will greatly improve our understanding of compression-driven crustal deformation processes associated with mountain building. These results will provide a means to critically evaluate the potential relationship between monsoon intensity and thrust fault propagation, as well as document the importance of Himalayan uplift and exhumation and chemical weathering on ocean chemistry. The isotopic seawater record of the ratios of osmium (187Os/188Os) as recorded in sedimentary rocks has been used as a proxy for global chemical weathering, and the results of this study will provide data with profound influences on future global oceanographic and climate models. In addition to the scientific objectives of this study, potential benefits to society and national interests include providing support for an early career researcher at a major research institution; graduate and undergraduate student training in a science, technology, engineering, and mathematics (STEM) discipline; with international collaboration of a U.S. graduate student and post-doctoral researcher with Indian scientists; education and outreach activities aimed at U.S. and Indian K-12 equivalent students; and development of web-based informational contributions for the general public. The project will promote broadening of participation of underrepresented groups in science, and the results of the work will dissemination of research results through professional science presentations, the peer-reviewed scientific literature, and incorporation of research results in into publicly accessible community databases. The project involves a high-resolution geo/thermochronometric investigation of bedrock and foreland basin deposits of the Himalayan frontal system in north India to constrain exhumation timing for distinct zones in the Lesser Himalaya. This work will focus on a series of strike-perpendicular transects across major thrust sheets for (Uranium-Thorium)/Helium dating of zircon and apatite, coupled with detailed facies analysis and provenance studies via zircon Uranium-Lead-Helium (U-Pb-He) double dating of foreland basin deposits. Contrasting models have been proposed for the sequence of thrust propagation of Lesser Himalayan blocks, notably the time of exhumation and structural affinities of the 'outer' Lesser Himalayan zone. These models postulate structural emplacement ages for the 'outer' Lesser Himalayan zone that range from the late Eocene to less than about 14 million years ago--a potential 14 to 30 million-year discrepancy. However, recent studies of foreland basin provenance data suggested the 'outer' Lesser Himalayan zone was likely exhumed at approximately 16 Ma, which corresponds with a noted increase in monsoon intensity. The weathering of 'outer' Lesser Himalayan zone rocks enriched in radiogenic 187Os has been tied to a pronounced increase in Neogene seawater 187Os/188Os at 16 million years ago. Our comprehensive study will constrain the sequence of thrust propagation and exhumation timing of the 'outer' Lesser Himalayan zone, allowing us to: 1) differentiate between contrasting kinematic models for Himalayan thrust belt evolution, and 2) test the hypothesis that exhumation and weathering of distinct Himalayan tectonic zones was the principal driver of secular changes in Neogene seawater chemistry. Preliminary (U-Th)/He geochronologic data offers intriguing support for the hypotheses of a direct link between Himalayan weathering and seawater chemistry.This award is co-funded by NSF's International Science and Engineering Section.