Crustal Anisotropy and Mantle Stratigraphy in the Tibetan Plateau and Central Andes

青藏高原和安第斯山脉中部的地壳各向异性和地幔地层

• 批准号: 0125121
• 负责人: George Zandt
• 金额: $ 10.12万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-04-15 至 2005-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0125121&HistoricalAwards=false
• 关键词: Crustal; Anisotropy; Mantle; Stratigraphy; Tibetan

The largest mountains and highest plateaus on Earth are built when continents collide. Seismic converted phases (receiver functions) are used to investigate two key questions in continental collisions: does the lower crust flow beneath high plateaus, and does continental mantle subduct beneath mountain belts? If crustal flow occurs in a relatively thin channel, as some modeling predicts, it would develop a strong structural or mineral fabric that may be identified by seismic anisotropy. Unlike shear-wave splitting studies that provide only bulk anisotropy information between the source and receiver, azimuthal variations of converted phases can constrain anisotropy parameters for layers within the crust. Previous studies have generally found crustal anisotropies 5%, but highly anisotropic (10%) layers within the crust have recently been identified in New Zealand and the Central Andes using the receiver function method. This new technique is being applied to receiver functions recorded across the highest elevations on Earth, the Tibetan Plateau, in order to search for evidence of large-scale crustal flow.The upper mantle beneath the stable interiors of continents is layered on a large scale. Some layer boundaries are observed regionally and denoted by seismologists as "H", "X", and "L". The origin of the stratification of the continental upper mantle is still poorly understood. In some locations the layering has significant dip. Receiver functions have been used to image modern subductions zones as well as identify dipping layers in the upper mantle beneath ancient cratons. Some of these layers beneath cratons appear to have anisotropic properties and may identify relict continental subduction zones. Even if the origin of the stratification is unknown, it can be used as a "tracer" to follow the subduction or destruction of an impinging strong plate beneath a continental collision zone, for example, to track the Indian plate beneath the Himalayas and Tibet.The primary goal of this project is to map out crustal anisotropy and upper mantle layering across the Tibetan Plateau, and use the results to improve our understanding of how high plateaus are built. This research will continue the development of the receiver function technique in the study of seismic anisotropy and mantle stratigraphy, and contribute to the technical education of two young scientists.

地球上最大的山脉和最高的高原是在大陆碰撞时形成的。地震转换相位（接收函数）被用来研究大陆碰撞中的两个关键问题：高原下地壳是否流动，以及大陆地幔是否俯冲到山脉带之下？ 如果地壳流动发生在一个相对较薄的通道中，正如一些模型预测的那样，它将发展出一个强大的结构或矿物组构，可以通过地震各向异性来识别。与只提供源和接收器之间的体各向异性信息的剪切波分裂研究不同，转换相位的方位角变化可以约束地壳内各层的各向异性参数。以前的研究一般发现地壳各向异性为5%，但最近在新西兰和中部安第斯山脉使用接收函数法确定了地壳内的高度各向异性（10%）层。这一新技术正被应用于地球上海拔最高的青藏高原所记录的接收器函数，以寻找大规模地壳流动的证据。大陆稳定内部之下的上地幔是大规模分层的。 有些层的边界是在区域上观察到的，地震学家用“H”、“X”和“L”表示。大陆上地幔分层的起源仍然知之甚少。在某些地方，地层有明显的倾斜。接收器功能已被用来成像现代俯冲带，以及确定倾斜层在上地幔下的古代俯冲带。其中一些地层下的岩石似乎具有各向异性的性质，并可能确定残留的大陆俯冲带。即使不知道分层的起源，它也可以作为一种“示踪剂”，跟踪大陆碰撞带下碰撞的强板块的俯冲或破坏，例如，跟踪喜马拉雅山和西藏下面的印度板块。这个项目的主要目标是绘制整个青藏高原的地壳各向异性和上地幔分层图，并利用这些结果来提高我们对高原是如何形成的理解。这项研究将继续发展接收函数技术在地震各向异性和地幔地层学研究中的作用，并有助于两位年轻科学家的技术教育。