摘要
通过对近年新获得的航磁、重力、大地电磁测深和地质等资料的综合研究揭示,羌塘西部隆起查桑段具有明显的南北分带、东西分块和垂向分层的结构、构造特征。该区总体由两(东部)、三(西部)个东西向展布的大型南倾构造块体推覆叠置而成,其间又被数条近南北向断裂分割为若干个断块。各块带出露地层时代、结构构造和地球物理场特征有较大差别。在查桑段及邻区,地壳中上部有两个低阻层,所在的深度分别为15±5km和约40km之下。壳内上部低阻层主要分布在查桑段及其以南,为各块体总体向北运动和逆掩叠覆之底部主拆离推覆面,该区各南倾大断裂均向下收敛并交会到该层。下部低阻层的展布超出了查桑段,向北已达北羌塘坳陷,其影响的范围可能更为广阔。此南北分带、多块叠置的结构和复杂多变的地球物理场特征,仅孤零零地出现在双湖—绒马之间,不具区域意义。其形成与该区东、西两侧中生代始存在的近南北向转换断层和晚古生代可能曾发育有裂谷之背景密切相关。该区段挤压变形和叠覆隆升,始于早白垩世羌塘盆地反转期;始新世以来,印度板块碰撞遂继续向北推挤,又得到进一步的发展、加强及改造。
Synthesize studying on the data of aeromagnetic survey, gravity survey, magnetotelluric sounding and geology investigation, which were received newly in recent years, shows that there are clear structure and tectonic features of belting in south-north trend, block-faulting in east-west trend and vertical sphere-laying in the Chasang section of western uplift of Qiangtang region. The Chasang section is formed, napped and superimposed in general by two (east part of the area) or three (west part of the area) big tectonic blocks with east-west strike and south direction of dip. This area is divided into several fault-blocks by the several nearly south-north trend fractures. There are bigger difference on the features of time of outcropping strata, structure and tectonic, geophysical field of every block and belt. There are two low-resistance layers, with the depth of 15 ± 5 km and nearly under 40 km separately, in the upper and middle crust of Chasang section and neighboring area. The intra-crustal upper low-resistance layer, which is a main detachment fault and nappe surface at the base of the several blocks with movement of north direction and thrusting and superimposing in general, is mainly located in the Chasang section and the south part of the area. These big fractures with south direction of dip in the region are all gathered down and converged to the fracture at the base of the region. Spreading of the lower-resistance layer is out of the scope of the Chasang section and extended at north direction to the north Qiangtang down-warping region and its affected scope may be more wide. The structure of belting in south-north trend and superimposing of multi-block, complex and various features of geophysical fields, only appeared lonely between Shuangla Co (Lake) and Rongma, and has no regional significance. Its formation not only has a close relation to nearly south-north trend transform fault existing at the beginning of Mesozoic Era on the both sides of east and west part of the region, but also has a close r
出处
《地质论评》
CAS
CSCD
北大核心
2002年第6期593-602,共10页
Geological Review
基金
国家重点基础研究发展规划项目(编号 G1998040808)
中国石油天然气集团公司"九五"科技工程项目资助的成果
关键词
青藏高原
羌塘盆地
查桑地区
结构构造
推覆叠置
后期改造
地理物理
地质构造
Qinghai-Tibet plateau
Qiangtang Basin
Chasang area
structure and tectonics
nappe and superimposing
later reformation
geophysics
