Collaborative Research: Deep Structure of the Northeast Tibetan Collision Zone- INDEPTH IV

这个项目（第四次调查）是以前资助的项目（第一、二、三次调查）的继续。纵深研究的首要目标是了解大陆与大陆碰撞时发生的基本过程。深度一、二、三是中美联合项目。研究以了解青藏高原和喜马拉雅山脉的形成，它们共同构成了地球上活跃的大陆-大陆碰撞带的典型例子。这些研究结果深刻地影响了这种构造背景下流行的造山理论。deep4的焦点是青藏高原的东北边界。这一边界在当代关于大陆高原形成是对碰撞造山运动的陆内反应的争论中起着中心作用。最近的地质研究和有限的地球物理测量表明，a)隆起是由于亚洲地壳的内部叠瓦“堆积”，而b)亚洲大陆岩石圈被分离并“俯冲”到西藏地幔中。这种模式与一种竞争性的模式形成对比，这种模式主要来自高原南部和东部的观测，将高原的形成归因于地壳深处的韧性流动。任何地表构造模型的关键是高原及其邻近地区的地幔动力学。北部高原下的上地幔地球物理性质不同地归因于由增厚岩石圈不稳定引发的剥离、地幔盖剥离和/或与印度大陆岩石圈俯冲相关的软流圈逆流。INDEPTH IV将通过在东北高原边界带的三个关键部分进行综合的、集中的地球物理调查计划来测试这些假设中的关键要素。地球物理调查将包括综合地震反射、折射和密集间隔的被动地震剖面、详细的大地电磁调查和区域宽带地震阵列。调查要调查的具体特征包括：a)拟议的莫霍偏移的存在和性质；B)高原边界主要逆冲断层的深部几何构造；C)逆冲断层与走滑断层的关系；D)构造连续性对下地壳流动的约束；e)俯冲亚洲岩石圈的存在和性质；f)高原前陆下岩石圈增厚模式。

This project (INDEPTH IV) is a continuation of previously funded projects (INDEPTH I, II, III). The overarching goal of the INDEPTH studies is to understand the basic processes that take place in a continent-continent collision. INDEPTH I, II, and III were joint Sino-U.S. studies to understand the formation of the Tibetan Plateau and Himalayan mountains, which together comprise Earth's type example of an active continent-continent collision zone. Results from these studies have profoundly influenced prevalent theories of mountain building in such tectonic settings. The focus of INDEPTH IV is the northeastern boundary of the Tibetan Plateau. This boundary plays a central role in a contemporary debate concerning continental plateau formation as an intracontinental response to collisional orogeny. Recent geological studies and limited geophysical measurements in this region have been cited to argue that a) uplift is due to internal imbricate "stacking" of Asian crust while b) Asian continental lithosphere is being detached and "subducted" into the Tibetan mantle. Such models contrast with a competing paradigm, derived primarily from observations in the southern and eastern portions of the Plateau, that attribute plateau formation to ductile flow in the deep crust. Critical to any model of surface tectonics is the mantle dynamics beneath the plateau and adjacent regions. Upper mantle geophysical properties beneath the northern plateau have been variously attributed to delamination triggered by instability of a thickened lithosphere, mantle lid detachment and/or asthenospheric counterflow associated with subduction of Indian continental lithosphere. INDEPTH IV will test key elements in these hypotheses with an integrated, focused program of geophysical surveys across three key segments of the NE Plateau boundary zone. Geophysical surveys will consist of integrated seismic reflection, refraction and densely spaced passive seismic profiles, a detailed magnetotelluric survey, and a regional broadband seismic array. Specific features to be investigated by the surveys include: a) the existence and nature of proposed Moho offsets; b) the deep geometry of major thrust faults at the plateau boundary; c) the relationship between major thrusts and strike slip faults; d) constraints on lower crustal flow from structural continuity of crustal markers; e) the existence and nature of subducting Asian lithosphere; and f) the mode of lithospheric thickening beneath the plateau foreland.