雪峰造山带北西缘永顺-大明逆冲推覆构造的厘定及其地质意义  

THE DETERMINATION OF YONGSHUN-DAMING THRUST-NAPPE STRUCTURE IN THE NORTHWESTERN MARGIN OF XUEFENG OROGENIC BELT AND ITS GEOLOGICAL IMPLICATIONS

作　　者：李泽泓 曾广乾 凌跃新 熊延旺 曾凡海 吴开彬 

机构地区：[1]湖南省地质调查院,湖南长沙410016 [2]贵州省地质调查院,贵州贵阳550005

出　　处：《矿物岩石》2017年第4期62-73,共12页Mineralogy and Petrology

基　　金：中国地质调查局扬子工程湘西-鄂西成矿带神农架-花垣地区地质矿产调查二级项目(No.DD20160029);贵州省地质矿产勘查开发局局管重大科研项目"贵州区域构造特征;构造演化与矿产空间分布关系研究"

摘　　要：通过1∶5×10~4区域地质调查及对重点区段的解剖,首次对湘西永顺-大明逆冲推覆构造的几何样式与变形特征进行详细研究。推覆构造总体呈北东—南西向展布,在逆冲推覆构造的前锋断层沿线,寒武系及奥陶系向北西逆冲推覆于奥陶系及志留系之上,形成规模不等的串珠状排列的飞来峰与构造窗。推覆主断层具有典型的台阶式结构特征,即推覆断层在寒武系上统和奥陶系以灰岩、白云岩为主的强硬岩层中形成高角度切层断坡,进入下志留统下部以泥岩、页岩为主的软弱岩层后断层倾角变缓,转为断坪。推覆构造沿走向变形强度以及结构特征存在明显变化,由北东往南西各区段的水平位移总体上呈现递减趋势,最大推覆距离约4km。永顺-大明逆冲推覆构造的厘定确证雪峰造山带北西缘推覆构造的存在,但诸多证据表明该区域并不存在大规模推覆作用,推覆体为准原地型。分析认为推覆构造是印支—燕山期在北西—南东向挤压应力场下递进变形的产物。Based on the 1=5 × 104 regional geological survey and key section investigation in the field, the geometrical pattern of the thrust-nappe structure in Yongshun-Daming area is studied in details. The nappe structure has a NE--SW trend, and the Cambrian and Ordovician strata thrus- ted northwestward on the Ordovician and Silurian strata, formed different scales of the klippes and structural windows in the beaded form. The major nappe thrust has a typical step texture, forming steep fault in the relative competent Cambrian and Ordovician limestones and becoming gentlely dipped when entering the relative imcompetent Silurian mudstone layers. The deforma- tion and style of the thrusts change along the strike of structural belt and the amount of horizon- tal displacement reduced from northeast to southwest as a whole, with a maximum displacement value of about 4 km. These deformatioin features in the Yongshun-Daming area indicate the exist- ence of nappe structures in the northwestern margin of Xuefeng orogenic belt. However,they are relatively small scale structures characteristic of parautochthonous nappes. It is considered that the nappe structure is resulted from the progressive deformation with NW--SE compressional stress field during India-Yanshan period.

关 键 词：逆冲推覆构造 几何学与运动学 飞来峰与构造窗 慈利-保靖断裂带 雪峰造山带 

分 类 号：P542[天文地球—构造地质学]