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

该项目（INDEPTH IV）是以前资助的项目（INDEPTH I、II、III）的延续。 INDEPTH研究的首要目标是了解大陆-大陆碰撞中发生的基本过程。 INDEPTH I，II和III是中美联合研究，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。 这些研究的结果深刻地影响了在这种构造环境中造山运动的流行理论。INDEPTH IV的重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陆内碰撞造山作用的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）隆升是由于亚洲地壳内部的叠瓦状“堆叠”，而B）亚洲大陆岩石圈正在拆离和“俯冲”到西藏地幔。 这种模型与主要来自高原南部和东部的观测的竞争范式形成对比，该范式将高原形成归因于地壳深部的韧性流动。 任何地表构造模型的关键是高原和邻近地区之下的地幔动力学。 北方高原下的上地幔地球物理性质被不同程度地归因于增厚岩石圈不稳定性引发的拆沉、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将在东北高原边界带的三个关键部分进行综合的、有重点的地球物理调查，以测试这些假设中的关键要素。 地球物理勘探将包括综合地震反射、折射和密集的被动地震剖面、详细的大地电磁勘探和区域宽带地震阵列。 调查将调查的具体特点包括： a）提议的莫霍面偏移的存在和性质; B）高原边界主要逆冲断层的深部几何形状; c）主要逆冲断层与走滑断层之间的关系; d）地壳标志物的结构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）高原前陆下方岩石圈加厚的模式。

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.