地学前缘 ›› 2008, Vol. 15 ›› Issue (6): 208-218.

• 论文 • 上一篇    下一篇

青藏高原东部及其邻区力学耦合的岩石圈变形模式

  

  1. 1中国地震局 地球物理研究所, 北京 100081
    2Carnegie Institute of Washington, DTM, Washington DC 20015, USA
    3Pudue University, West Lafayette, IN 47907, USA

  • 出版日期:2008-06-20 发布日期:2008-06-20
  • 作者简介:王椿镛(1945—),男,研究员,固体地球物理学专业,主要从事地球内部构造和地球动力学研究。E-mail: wangcy@cea-igp.ac.cn
  • 基金资助:

    国家自然科学基金项目(40334041, 40774037);科学技术部重点国际合作项目(2003DF 000011)

A model of mechanically coupled deformation in lithosphere beneath the eastern Tibetan Plateau and its vicinity.

  1. 1Institute of Geophysics, China Earthquake Administration, Beijing 100081, China
    2Carnegie Institute of Washington, DTM, Washington  DC 20015, USA
    3Pudue University, West Lafayette, IN 47907, USA

  • Online:2008-06-20 Published:2008-06-20

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摘要：

根据青藏高原东部及其邻区布设的143个宽频带固定和流动地震台站的远震记录的SKS波分裂分析获得了各台站的快波偏振方向和快慢波之间的时间延迟。SKS分裂分析结果总体上反映了高原东部的上地幔物质流动方向,即高原内部表现为环绕喜马拉雅东构造结的顺时针旋转。在造山运动过程中有关岩石圈地壳和地幔力学耦合的造山变形方式,用从GPS和第四纪断裂滑动速率数据确定的地面变形场和由地震波各向异性数据推断的地幔变形场联合分析来定量求得。在青藏高原东部和云南、四川等地区新近快速增加的GPS和SKS波分裂观测数据,提供了对青藏高原岩石圈地幔实际变形方式的检验。这些新的数据不仅加强了高原内部力学耦合岩石圈的证据,而且也解释了高原外部相同的耦合特征。文中引入简单剪切变形和纯剪切变形的概念,用于解释高原内外不同的耦合变形特征。青藏高原和周围区域力学耦合岩石圈的垂直连贯变形有两个方面的大陆动力学含义:第一,岩石圈垂直强度剖面被一个重要的条件所约束,即要求与重力势能变化相关的应力能够从地壳传递到地幔;第二,青藏高原各向异性的空间变化反映了一个岩石圈变形的大尺度模式,以及从高原内部的简单剪切变形向高原外部的纯剪切变形的过渡带。文中提出的力学耦合岩石圈变形模型与当前已有的多种造山运动变形模型具有不同的变形含义,因此,地幔变形在青藏高原隆升过程中起主要作用。

关键词: 青藏高原;岩石圈变形;力学耦合;地震波各向异性;垂直连贯变形

Abstract:

Based on the SKSwave splitting analysis on the seismic records at 143 broadband permanent and temporary stations deployed in the eastern Tibetan Plateau and its vicinity, we have determined the fast polarization direction and delay time between fast and slow waves at individual stations; the pattern of SKSsplitting fast polarization direction exhibits the flow direction of upper mantles material in the eastern Tibetan Plateau, i.e., the clockwise rotation around the Eastern Himalayan Syntaxis. The style of orogenic deformation can be quantitatively evaluated by the joint analysis of the surface deformation field, as inferred from GPS and Quaternary fault slip, and the mantle deformation field from seismic anisotropy. The greatly expanded data set of surface deformation (GPS) and seismic anisotropy (SKS splitting) from eastern Tibet, Yunnan and Sichuan regions provides a stringent test for the manner in which the Tibetan lithosphere actually deforms. These new data not only strengthens the evidence for the coupled deformation onplateau, but also argues this same property offplateau. The vertically coherent deformation of a mechanicallycoupled lithosphere for Tibet and its vicinity has two implications for continental dynamics. First, the lithospheric vertical strength profile is constrained by the requirement that GPErelated stresses are being efficiently transmitted from the crust into the mantle. Second, the observed spatial variations in anisotropy reflect the largescale pattern of lithospheric deformation, as well as a transition in deformational style from simple shear on the Tibetan Plateau to pure shear offplateau. The model of mechanicallycoupled deformation in lithosphere presented in this paper has different implications from the previously presented models of orogenic deformation. Therefore, the mantle deformation plays a major role in the uplift process in the Tibetan plateau.

Key words:

Tibetan Plateau; lithospheric deformation; mechanical coupling; seismic anisotropy; vertically coherent deformation

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