Timing, Conditions, and Rates of Thrust Transport in the Nepalese Himalaya

首席研究员为朗塘地区高级岩石开发的新岩石学和年代学方法（尼泊尔中东部）表明，自大约2000万年前以来，逆冲断层运动速率通常与印度次大陆的会聚一致，约为2厘米/年（相当于现代速率），但逆冲速率是可变的，一个逆冲席的就位速率是平均速率的2-3倍。这些数据还突出了在过去的3-4百万年中，快速侵蚀（5-10毫米/年）在挖掘变质岩中的重要性。拟议研究的目的是测试这些模式是否也在其他两个地区-西部的安纳普尔纳地区和尼泊尔远东的阿伦地区-以及测试大喜马拉雅序列是否经历了高压或超高压变质作用。采用了以下方法：（1）独居石颗粒化学填图和定量微区分析，以及离子探针测年。这些年龄记录了冷却的时间，对于许多结构层次来说，冷却是推力运动的直接结果。(2)通过已发表的喜马拉雅热模型确定压力-温度条件并转换为古位置。位移量、冷却时间和每片的推力运动被转换成推力率的估计值。(3)确定了阿荣地区榴辉岩的年龄和P-T条件，以确定它们是否与喜马拉雅早期变形有关。这项工作对构造研究及其与侵蚀和地球化学演化的相互关系具有重要的广泛意义。这项工作还将支持一名地球化学/构造学研究生的教育。

A new petrologic and chronologic approach developed by the principal investigator for high-grade rocks in the Langtang region (east-central Nepal) demonstrates that thrust fault movement rates since about 20 million years ago are generally consistent with convergence of the Indian subcontinent at about 2 cm/yr (equivalent to modern rates), but that thrust rates were variable, with emplacement of one thrust sheet at a rate 2-3 times the average rate. These data also highlight the importance of rapid erosion (5-10 mm/yr) in exhuming metamorphic rocks over the last 3-4 million years. The purpose of the proposed research is to test whether these patterns are also found in two other areas - the Annapurna region to the west, and the Arun region in far eastern Nepal - and to test whether the Greater Himalayan Sequence experienced high-pressure or ultra-high-pressure metamorphism. The following methods are being used: (1) Chemical mapping and quantitative microanalysis of monazite grains, and dating of chemically distinct domains via ion microprobe. These ages are documenting the timing of cooling, which for many structural levels is a direct result of thrust movement. (2) Determination of pressure-temperature conditions and conversion to paleoposition via published thermal models for the Himalaya. The amount of displacement, and timing of cooling and thrust movement for each sheet is being converted to estimates of thrust rate. (3) Determination of ages and P-T conditions of eclogites in the Arun region to determine whether these are related to early Himalayan deformation. This work has major broad implications for tectonics research and its interrelationship with erosion and Earth's chemical evolution. This work will also support the education of one graduate student in geochemistry/tectonics.