Geometry and kinematics of the Main Himalayan Thrust and Neogene crustal exhumation in the Bhutanese Himalaya derived from inversion of multithermochronologic data
Geometry and kinematics of the Main Himalayan Thrust and Neogene crustal exhumation in the Bhutanese Himalaya derived from inversion of multithermochronologic data
复制标题
DOI：
10.1002/2013jb010891
复制
发表时间：
2014-02-01
影响因子：
3.9
通讯作者：
Duncan, Chris
中科院分区：
文献类型：
--
作者：
Coutand, Isabelle;Whipp, David M.;Duncan, Chris
气候和构造作用都影响汇聚造山带的基岩侵蚀和折返，但确定它们各自的影响是困难的。必要的第一步是量化造山带内的长期侵蚀速率(类似于10(6)年)。在喜马拉雅山脉，过去的研究表明，沿着山脉前缘，长期的侵蚀速率在空间和时间上都不同，导致了许多构造模型来解释观测到的侵蚀速率分布。在这里，我们反演了大量新的和现有的热年代学年代学数据，以确定不丹东喜马拉雅地区新近纪构造活动的长期折返速率和运动学。新数据包括31个磷灰石和5个锆石(U-Th)/He年龄，49个磷灰石和16个锆石裂变径迹年龄，沿着不丹西部和东部造山带的两个南北方向的断面。数据反演是使用三维热运动学模型Pecube的修改版本进行的，参数范围由可用的地质年代学、变质、构造和地球物理数据定义。在几个重要的观察结果中，我们的三个主要结论如下：(1)热年代学年龄与主要断裂带的地表痕迹在空间上没有相关性，但似乎反映了喜马拉雅主冲断带的几何学特征；(2)我们的数据符合强烈的构造影响，涉及喜马拉雅主冲断带的不定倾角几何学和稳定地形；(3)不丹西部的侵蚀速率在过去10 Ma左右保持不变，而不丹东部在6 Ma左右出现侵蚀速率显著下降，我们部分将这种下降归因于会聚分裂为石龙高原的隆起。
Both climatic and tectonic processes affect bedrock erosion and exhumation in convergent orogens, but determining their respective influence is difficult. A requisite first step is to quantify long-term (similar to 10(6)year) erosion rates within an orogen. In the Himalaya, past studies suggest long-term erosion rates varied in space and time along the range front, resulting in numerous tectonic models to explain the observed erosion rate distribution. Here, we invert a large data set of new and existing thermochronological ages to determine both long-term exhumation rates and the kinematics of Neogene tectonic activity in the eastern Himalaya in Bhutan. New data include 31 apatite and five zircon (U-Th)/He ages, and 49 apatite and 16 zircon fission-track ages along two north-south oriented transects across the orogen in western and eastern Bhutan. Data inversion was performed using a modified version of the 3-D thermokinematic model Pecube, with parameter ranges defined by available geochronologic, metamorphic, structural, and geophysical data. Among several important observations, our three main conclusions are as follows: (1) Thermochronologic ages do not spatially correlate with surface traces of major fault zones but appear to reflect the geometry of the underlying Main Himalayan Thrust; (2) our data are compatible with a strong tectonic influence, involving a variably dipping Main Himalayan Thrust geometry and steady state topography; and (3) erosion rates have remained constant in western Bhutan over the last similar to 10Ma, while a significant decrease occurred at similar to 6Ma in eastern Bhutan, which we partially attribute to convergence partitioning into uplift of the Shillong Plateau.