慈利—保靖断裂带大地电磁测深研究

Tectonic characteristics of Cili-Baojing fault zone based on MT data

慈利—保靖断裂带是雪峰山基底隆升带的西北缘边界。前人对断裂带及邻域的地质认识主要基于地面地质调查和少量地震勘探资料,区域构造研究中对断裂带的构造属性一直存有争议。本文通过多条横跨该断裂带的大地电磁测深反演电阻率剖面,结合重力资料和岩石物性测试结果进行了电性构造分布特征综合解释。结果表明:慈利—保靖断裂带由多条不同尺度且大致平行的正、逆断裂组成;主断裂北陡南缓,收敛于基底滑脱面,不是深切岩石圈的深大断裂;该断裂带作为雪峰山隆升带与扬子地台湘西北褶皱带的分界是合理的;在沅麻盆地的东缘,由于基底拆离上推,沅古坪—沅陵向斜中的寒武系以下地层被推覆构造掩覆深埋,可能成为常规油气或页岩气勘探的有利目标区。

Cili-Baojing fault zone is located in the northwest boundary of Xuefeng mountains uplift belt.The current geological knowledge about this fault zone and neighboring areas is mainly based on geological field surveys and few seismic data,so there is a dispute about understanding of tectonic characteristics in the zone.We interpret geoelectric structural features based on the resistivity inverted from magnetotelluric(MT)data combined with gravity data,and the laboratory core test data in the zone.The following understandings are obtained based on our study:A.Cili-Baojing fault zone consists of several nearly-parallel reverse and normal faults;B.The major fault is steep in the north and gentle in the south,and converges to the base detachment surface;C.It is reasonable to regard this fault zone as the boundary between the northwestern margin of Xuefeng uplift belt and the Yangtze Platform;D.Lower Cambrian formations in YuangupingYuanling syncline deep-buried by overthrusts at the east margin of the Yuanma Basin may be a favorable zone for conventional oil and gas or shale gas exploration.