西藏南部聂拉木地区前寒武纪岩石磁组构及其构造意义  

CHARACTERISTICS OF PRECAMBRIAN ROCK MAGNETIC FABRICS IN THE NYALAM AREA OF THE SOUTHERN TIBET AND ITS TECTONIC SIGNIFICANCE

作　　者：邹光富[1] 庄忠海[1] 潘忠习[1] 朱同兴[1] 陈永明[1] 

机构地区：[1]成都地质矿产研究所,成都610082

出　　处：《物探化探计算技术》2007年第4期326-333,共8页Computing Techniques For Geophysical and Geochemical Exploration

基　　金：国家自然科学基金项目(40272012)

摘　　要：通过对西藏南部聂拉木地区前寒武纪岩石磁组构进行研究表明：该区岩石磁化率百分率的各向异性胃值较高，均大于10％，这说明岩石曾经历了较强烈的韧性变形。根据岩石最小磁化率从主轴硒方向推断的岩石变形期，最大的主压应力方位主要有SN向、NE—SW向、NW—SE向。岩石磁组构费林（Flinn）图解表明，大部分岩石磁组构具有磁面理发育、磁线理不发育，岩石磁化率量值椭球体呈压扁状的特点。部分岩石磁组构还具有磁线理发育、磁面理不发育，岩石磁化率量值椭球体呈拉长形的特点。因此，该区域构造应变型式具有压缩应变和拉伸应变二种型式。岩石磁组构研究还表明，该区具有SN向挤压、NW—SE向挤压、NW—SE向伸展滑脱三期构造应力。这说明高喜马拉雅结晶基底岩石曾经历了SN向逆冲推覆构造作用，NW—SE向逆冲推覆构造作用和NW—SE向伸展滑脱构造作用过程。构造应力场的转变及其构造作用，为印度板块与欧亚板块之间，自白垩纪末～始新世晚期发生的弧～陆、陆～陆碰撞，和始新世晚期以来，强烈的陆内汇聚造山与青藏高原剧烈隆升，及区域伸展滑脱构造作用过程的响应。This paper reports Precambrian rock magnetic fabrics in the Nyalam area of the southern Tibet. The analytical results of magnetic fabrics show that the values of H are high(>10% in general), so that the ductile deformations of the Precambrian rock is strong. The orientation of the maximum principal stress inferred from the minimum magnetic susceptibility is nearly S-N, NE--SW,NW-SE and NW-SE. The Flinn diagram of the magnetic fabrics shows that the strain pattern are oblate and constrictional type. Magnetic foliation of the majority rock samples is well developed and the magnetic lineation is poor and the magnetic susceptibility ellipsoid is flattened. The magnetic lineation of the minority rock samples is well developed and the magnetic foliation is poor and the magnetic susceptibility ellipsoid is prolate. According to the geological field and the magnetic fabrics, there are 3 times tectonic stress field in SN directed extruding、NW-SE directed extruding、NW-SE directed extension. It shows that the Nyalam area has undergone process the orientation of SN, NW-SE nappe structure and NW-SE directed extension structure. The change of tectonic stress is reflected by the field characteristics of the Precambrian rock magnetic fabrics that is the direct responding result of the arc-continental, continent-continental collision between the India and Asian continents in the late part of the Late Cretaceous to Late Eocene and subsequently shifted to intra-continental convergent, the plateau uplifting and extension structure stage since the Late Eocene.

关 键 词：磁组构:构造变形分析 前寒武纪岩石 西藏南部聂拉木地区 

分 类 号：P542[天文地球—构造地质学]