ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    西秦岭临潭-岷县-宕昌断裂带新生代运动学历史及动力学分析

    Cenozoic Kinematic History of the Lintan-Minxian-Tanchang Fault in Western Qinling and Its Dynamic Process

    • 摘要: 临潭-岷县-宕昌断裂带是青藏高原东北缘西秦岭腹地具有构造边界性质的区域断裂带之一,它由多条近于平行的逆冲-走滑断层组成。通过对其主要断层之一的小寨-浦麻断层(F3)典型断层带内断层岩类型和分带特征、构造要素的几何学-运动学特征及构造截切关系等观测分析,表明其主要为新生代形成的一条脆性断层,至少经历了3期具有不同几何学-运动学特征的构造活动历史。第一期表现为向北北东陡倾(倾角为70°~80°)的自北向南高角度逆冲作用;第二期表现为向北北东中等倾斜(倾角为30°~50°)的自北向南逆冲作用;而第三期则表现为向南西陡倾(倾角为60°~70°)的左旋走滑作用。根据断层卷入的最新地层时代、三期变形构造要素产状及截切关系和青藏高原东北缘新生代以来区域断裂活动、沉积盆地演化和地壳隆升过程分析,认为第一期挤压逆冲作用起始于始新世中期(45~50 Ma左右)持续到渐新世初期;第二期挤压逆冲作用发生在中新世末或上新世初,持续到早第四纪;而第3期左旋走滑作用只是晚第四纪以来的构造作用。临潭-岷县-宕昌断裂带的小寨-浦麻断层的三期构造活动可能记录了印度板块与欧亚板块碰撞汇聚过程不同阶段在西秦岭的构造动力学响应。第一期挤压逆冲作用可能与印度-欧亚汇聚碰撞高峰期(55~45 Ma)地壳的挤压缩短作用的远程效应有关;而第二期的逆冲作用与青藏高原地壳增厚和高原隆升向东北缘的扩展作用相联系;第三期左旋走滑作用则是晚第四纪以来的构造活动,明显滞后于5 Ma青藏高原腹地的东西伸展和挤出走滑作用,这有可能暗示着青藏高原东北缘断裂构造活动及地壳隆升过程与青藏高原腹地并不同步。这为新生代以来印度板块-欧亚板块碰撞作用是逐渐向北扩展生长过程提供了构造地质学约束。

       

      Abstract: The Lintan-Minxian-Tangchang Fault (abbreviation as LMTF) is one of main boundary faults in the hinterland of Western Qinling, which is located at the northeastern margin of the Qinghai-Tibet plateau. It consists of several nearly parallel thrusting-strike slipping faults. Taking the typical section of Pu-Ma fault (F3) of the LMTF as the studying object, the detailed investigation has been carried out for the types and zoning of fault rocks, geometry-kinematics characteristics of various structural elements. The results indicated that F3 fault is mainly a typical shallow level brittle fault, which experienced at least three phase deformation with different geometric-kinematic characteristics since the Cenozoic era. The first phase deformation is characterized by high angle thrusting from north to south, with NNE steep dipping (dip angle around 70°~80°); the second by medium angle thrusting from north to south, with NNE medium dipping (dip angle around 30°~50°); and the third by sinistral strike-slipping, with NW trending and SW dipping (dip angle around 60°~70°). Based upon comprehensive analysis for the involved strata ages, structural cutting relationship in the fault zone, the regional fault activities, sedimentary basin evolution and crustal uplifting in northeast margin of Qinghai-Tibet plateau since Cenozoic era, it is suggested that the first period high angle thrusting was occurred at beginning of middle Eocene (40~50 Ma), which maybe continued to beginning of Oligocene; the second period medium angle thrusting was occurred at end of Miocene or beginning of Pliocene, which maybe continued to early Quaternary; and the third period sinistral strike-slipping was just the tectonic event occurred since late Quaternary. Three period fault activities of F3 fault in LMTF mentioned above maybe documented the remote tectonic responses of the West Qinling to the three different evolution stages during the collisional converge between India and Eurasian plates. First period high angle thrusting could be related to the compression shortening during India-Eurasia peak collision (55~45 Ma); the second period medium angle thrusting was stood for the out-spreading of crustal thickening and uplifting of Qinghai-Tibet plateau; the third period sinistral strike-slipping was obviously lagged to E-W extension and NW trending strike-slipping, which may indicate the unsynchronized uplifting and strike-slipping in the northeastern margin of Qinghai-Tibet plateau and the hinterland of Qinghai-Tibet plateau. These results may reflect that the present entire Tibetan plateau has been forming by the gradual propagation to the northeast.

       

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