大陆岩石圈解耦及块体运动讨论——以青藏高原—川滇地区为例  

CONTINENTAL LITHOSPHERE DECOUPLING:IMPLICATION FOR BLOCK MOVEMENT

作　　者：杨晓松[1] 马瑾[1] 

机构地区：[1]中国地震局地质研究所地震动力学实验室,北京100029

出　　处：《地学前缘》2003年第U08期240-247,共8页Earth Science Frontiers

基　　金：国家重点基础研究发展规划项目 (G19980 40 70 0 ) ;国家自然科学基金资助项目 (4 0 0 72 0 62 ) ;地震科学联合基金项目

摘　　要：块体构造理论的发展不断地深化着人们对现今大陆岩石圈运动 ,尤其是大陆强震的孕育和发生规律的认识。块体底部边界的构造性质是块体运动的核心问题之一 ,同时也是块体构造理论研究中的薄弱环节。确定块体底部边界的岩石物理性质是利用地球物理方法探测和识别块体底部边界的前提。文中依据现代实验岩石学、实验岩石物理学、地球物理学、地质学等的研究成果 ,对块体底部边界之成因属性和岩石物理性质进行了分析。将大陆块体划分为两种基本类型———地壳型块体和岩石圈型块体。地壳型块体是由大陆上部地壳所构成的“薄板” ,壳内软弱带的顶面为其底部边界和潜在的解耦带。岩石圈型块体在岩石圈尺度上是力学耦合的 ,以上地幔软流圈的顶面为其底部边界。壳内软弱带具有垂直方向低速和各向异性的基本特征 ,联合多种地震测深方法有望确定块体的底界。在现今构造活动区内 ,地壳型块体的潜在解耦带可能由壳内部分熔融带承担。青藏高原南部—川滇地区 2 0 35km的深度上广泛存在低速带。地热、岩石学、实验岩石学和模拟均显示该地区的低速带具有部分熔融的成因属性。块体沿着该壳内低速层与下伏地壳发生某种程度解耦。It is necessary to determine the petrophysical features of the weak layers of underlain blocks for identifying them by geophysical surveys and for understanding the block movement. However, we have little knowledge about the nature and structural features of the layers to date. On the basis of the data of modern petrological and petrophysical experiments, geophysical surveys and geological investigations, the authors have discussed the petrophysical characteristics of the layers. Blocks can be divided into two typical kinds—the crustal block and the lithospheric block. The former is the “thin plate” constituted by the upper part of crust that lies on an intracrustal weak layer or potential decoupling zone along which the crustal block can move independently to some extent. The latter is mechanically coupled in lithosphere scale, and consequently it lies on asthenosphere and the top of asthenosphere is regarded as its bottom. The distinguishable features of the intracrustal weak zone are both low velocity when seismic waves pass though the layer perpendicularly and anisotropy. Therefore, it is expected to detect the zone by multi-seismic methods. Generally, in active tectonic regions, intracrustal partial melting zone is one of candidates to cause the upper part of crust (crustal block) to decouple to the other part of lithosphere. The low velocity zones attributed to partial melting occur within the depth of 20~35 km in southern Tibet and Sichuan-Yunnan extensively. The blocks in these areas are partially decoupling along the low velocity zones.

关 键 词：块体 壳内软弱带 低速层 各向异性 部分熔融 青藏高原—川滇地区 

分 类 号：P31[天文地球—固体地球物理学] P542[天文地球—地球物理学]