Collaborative Research: Lhasa Block Top to Bottom--Lithospheric Evolution of Asia's Leading Edge

喜马拉雅山？几十年来，西藏造山系统一直是广泛研究的主题，并继续成为了解造山过程和大陆演化的富有成果的实验室。地质和地球物理的研究提供了重要的见解，现代系统的结构和动力学，但传授较少的信息造山带？的早期发展，碰撞大陆的特点，可能会影响随后的演变。 该项目的目标是调查地壳和岩石圈厚度如何在西藏南部的变化，以建立？边界条件？印度-欧亚大陆碰撞（~50 My前）以及碰撞期间和之后岩石圈厚度的变化。 岩石圈厚度定义了地壳和岩石圈的热状态和流变性，是理解碰撞过程中地壳和岩石圈变形本质所必需的重要边界条件和性质。岩石圈厚度将综合地球化学、地质年代学、古高程、地震学、构造学、和模拟，以了解碰撞前的结构和演化的前缘南亚大陆边缘？拉萨街区？以及它在控制更广阔造山带发展中的作用。 他们试图回答两组相关的问题：？拉萨地块从碰撞到现在的地壳厚度是如何演变的？随着时间的推移，海拔和剥蚀历史是如何变化的？变质作用在改变地壳流变学和密度方面起什么作用， 促进地表隆起和侵蚀？？岩石圈变形对该区域增厚的贡献是什么？这组问题是相关的，因为地壳厚度和地表高程的方式可以影响造山带的力学。第二组相关的问题解决了拉萨块体的后期演化：？碰撞后岩浆的起源是什么？熔融在多大程度上促成了地壳的弱化和流动？岩浆和水流体及其分布的横向不均匀性如何影响拉萨地块的演化和变形？为什么拉萨地块的海拔高度相对一致，尽管地质、发掘和深部结构存在相当大的差异？这些问题的重要性来自于流变学及其空间变化在决定造山带如何在大尺度和小尺度上变形方面所起的控制作用。

The Himalaya?Tibet orogenic system has been the subject of extensive research for decades, and continues to be a fruitful laboratory for understanding orogenic processes and continental evolution. Geological and geophysical studies have provided important insights into the structure and dynamics of the modern system, but imparted less information about the orogen?s early development, and the characteristics of the colliding continents that may affect subsequent evolution. The goal of this project is to investigate how crustal and lithospheric thickness changes in southern Tibet in order to establish the ?boundary conditions? for the India-Eurasia collision (~50 My ago) and how lithosphereic thickness changes during and after collision. As pointed out by the PIs, lithospheric thickness defines the thermal state and rheology of the crust and lithosphere, which are important boundary conditions and properties necessary for understanding the nature of crustal and lithospheric deformation during collision.The PIs will integrate geochemistry, geochronology, paleoelevation, seismology, tectonics, and modeling to understand the pre-collision structure and evolution of the leading edge of the southern Asian continental margin ? the Lhasa block ? and its role in controlling the development of the broader orogen. They seek to answer two sets of related questions:? How has the crustal thickness of the Lhasa block evolved from collision to the present?? How have the elevation and denudation histories changed through time?? What role does metamorphism play in altering crustal rheology and density and as a consequence facilitate surface uplift and erosion?? What is the contribution of lithospheric deformation to thickening of the region?This set of questions is relevant because of the way crustal thickness and surface elevation can influence the mechanics of an orogen.The second set of related questions addresses the later evolution of the Lhasa block:? What is the origin of post-collisional magmas?? To what extent has melting contributed to crustal weakening and flow?? How have magmatic and aqueous fluids and lateral heterogeneity in their distribution influenced evolution and deformation of the Lhasa block?? Why are elevations in the Lhasa block relatively uniform despite considerable variations in geology, exhumation, and deep structure?The importance of these questions derives from the control that rheology and its spatialvariations play in determining how orogens deform at large and small scales.