Probing the Rheology of Tibetan Lithosphere: Surface Deformation in Response to Climatically-Induced Changes in Lake Loads

探讨青藏高原岩石圈的流变性：气候引起的湖泊荷载变化引起的地表变形

• 批准号: 0911587
• 负责人: Eric Kirby
• 金额: $ 45.99万
• 依托单位: Pennsylvania State Univ University Park
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-01-01 至 2013-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0911587&HistoricalAwards=false
• 关键词: Probing; Rheology; Tibetan; Lithosphere; Surface

This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).Direct measurements of the deformational properties of actively deforming lithosphere remain elusive and lead to fundamental gaps in the understanding of how the evolution of rheology controls the evolution of orogenic systems. Despite abundant geophysical and geological data for the Indo-Asian collisional orogen, the mobility of the lower crust beneath central Tibet, its physical state, and the role that localized channel flow has played in the evolution of the Plateau and the Himalaya remain first-order questions. This project focuses on characterizing the deformational response of Tibetan lithosphere to time-varying surface loads to place quantitative constraints on the rheology of the crust. The project utilizes flights of relict shorelines around several large lakes within the internally-drained interior of the Tibetan Plateau. These shorelines indicate former positions of more extensive lake levels, and the withdrawal of the lakes in response to climatically-driven hydrologic changes represents a load removed from the lithosphere. Because the shorelines represent a paleo-horizontal datum, deflection of these markers during flexural isostatic rebound can place constraints on the elastic strength of the lithosphere and the viscosity of the underlying substrate. The study will couple detailed field observations and geochronology with rigorous deformational modeling (elastic flexure and 3-D visco-elastic deformation) to link the history of lake unloading to physical properties of the lower crust and mantle. In doing so, two fundamental questions about the Tibet-Himalayan orogen will be addressed: (1) Is Tibetan crust capable of lateral flow on geologic timescales, and (2) Do the rheologic properties of Tibetan lithosphere vary among the individual terranes comprising the plateau? The answers to these questions extend far beyond the specifics of the Tibet-Himalayan orogen and will provide additional constraints on the conditions that favor or impede lower-crustal flow during orogenesis in both active and ancient mountain belts.Deformation within the deep crust is a fundamental process that links the driving forces for plate tectonics - flow in the earth's mantle - to slip on tectonic faults in the upper, brittle crust. Because direct measurements of the physical properties of the deep crust are technically infeasible, the behavior of the deep crust during mountain building is hotly debated. In particular, whether the deep crust is capable of widespread, lateral flow has implications for both strain accumulation on plate boundary fault systems - transient deformation along the Cascadia margin in the Western US is thought to be related to deformation in the deep crust - as well as the rates and patterns of development of high topography in Asia. The latter problem is one of great interest in that high topography of the Tibetan Plateau fundamentally influences atmospheric circulation. Understanding the processes and rates by which this high topography developed will enable more rigorous tests of the possibility that growth of the Tibetan Plateau played a central role in climate change over geologic timescales. This study will yield new insight into the nature of deformation within the deep crust beneath Tibet, information that is sorely lacking in today?s models of mountain building. In doing so, the project will also provide new constraints on climatically-driven changes in lake levels, information that is central to a more comprehensive understanding of the water budget in this resource-limited part of the world. Finally, the results will guide a more general understanding of how flow in the deep crust influences the overall deformation of the earth?s surface, including the potential for earthquake-generating slip on tectonic faults.

该奖项是根据2009年美国复苏和再投资法案（公法111-5）资助的。对活跃变形岩石圈的变形性质的直接测量仍然难以实现，并导致对流变学演化如何控制造山系统演化的理解存在根本性空白。尽管印度-亚洲碰撞造山带有丰富的地球物理和地质资料，但西藏中部下地壳的活动性、其物理状态以及局部河道流在高原和喜马拉雅演化中所起的作用仍然是一级问题。该项目的重点是描述西藏岩石圈对随时间变化的地表载荷的变形响应，从而对地壳流变学进行定量约束。该项目利用了青藏高原内部排水的几个大型湖泊周围的残留海岸线。这些海岸线表明以前的位置更广泛的湖泊水平，和湖泊的退缩，以应对气候驱动的水文变化代表了从岩石圈中删除的负载。由于海岸线代表了一个古水平基准面，挠曲均衡反弹过程中这些标记的偏转可以限制岩石圈的弹性强度和底层基底的粘度。这项研究将把详细的实地观察和地质年代学与严格的变形建模（弹性挠曲和三维粘弹性变形）结合起来，把湖泊卸载的历史与下地壳和地幔的物理性质联系起来。在这样做的时候，两个基本的问题，西藏-喜马拉雅造山带将被解决：（1）西藏地壳能够横向流动的地质时间尺度，（2）西藏岩石圈的流变特性之间的个别岩石圈组成的高原变化？这些问题的答案远远超出了西藏-喜马拉雅造山带的具体情况，并将提供额外的约束条件，有利于或阻碍造山作用期间的下地壳流动在活动和古老的山脉带。地壳深部的变形是一个基本的过程，连接板块构造的驱动力-在地幔中的流动-在上部，脆地壳的构造断层上滑动。由于直接测量地壳深部的物理性质在技术上是不可行的，因此地壳深部在造山过程中的行为引起了激烈的争论。特别是，无论是地壳深部是能够广泛的，横向流动的影响，应变积累的板块边界断层系统-瞬态变形沿着卡斯卡迪亚边缘在美国西部被认为是在地壳深部变形-以及在亚洲的高地形的发展速度和模式。后一个问题是一个非常感兴趣的，因为青藏高原的高地形从根本上影响大气环流。了解这种高地形发展的过程和速度将使更严格的测试的可能性，青藏高原的增长发挥了核心作用，在地质时间尺度的气候变化。这项研究将产生新的洞察变形的性质在地壳深部西藏之下，信息是非常缺乏的今天？山建筑的模型。在这样做的过程中，该项目还将提供对气候驱动的湖泊水位变化的新限制，这些信息对于更全面地了解世界上这个资源有限地区的水资源预算至关重要。最后，结果将指导更广泛的了解如何在地壳深处的流动影响地球的整体变形？的表面，包括潜在的地震产生滑动的构造断层。