西南天山柯坪逆冲推覆构造带的地壳缩短分析  

THE ANALYSIS FOR CRUST SHORTENING OF KALPIN THRUST TECTONIC ZONE, SOUTH-WESTERN TIANSHAN, XINJIANG, CHINA

作　　者：杨晓平[1] 冉勇康[1] 宋方敏[1] 徐锡伟[1] 程建武[1] 闵伟[1] 韩竹军[1] 陈立春[1] 

机构地区：[1]中国地震局地质研究所,北京100029

出　　处：《地震地质》2006年第2期194-204,共11页Seismology and Geology

基　　金：中国地震局"新疆巴楚-伽师6.8级地震应急工作专项计划"项目资助

摘　　要：柯坪逆冲推覆构造带是西南天山山前晚新生代以来形成的活动逆断裂一褶皱带，由5～6排近平行的弧形褶皱带组成，出露地层为寒武系一第四系。背斜形态多为复式箱状背斜和不对称的斜歪背斜，分别与断层弯曲背斜和断层扩展背斜的几何形态一致。地震勘探资料显示，各褶皱带前缘活动逆断裂在深部归并于统一的、由寒武系中的石膏层组成的滑脱面。滑脱面深度具有南浅北深、东浅西深的特点，皮羌断裂西侧滑脱面深度约为9kin，东侧滑脱面深度为5km。在柯坪逆冲推覆构造中部的皮羌断裂东西两侧各5kin和8kin的位置，以断层弯曲褶皱和断层扩展褶皱构造模型为指导，用线长平衡的方法完成了2条长度分别为78kin和73kin的平衡地质剖面，恢复到变形前的形态后计算出这2条剖面上的地壳缩短量分别为40kin和45km，缩短率为33％和37％。由于对柯坪逆冲推覆构造开始形成时间的证据较少，所以要计算长期的缩短速率是比较困难的。对比天山南麓库车活动逆断裂一褶皱带的形成时代，以及柯坪逆冲推覆构造与印干断裂的关系，认为柯坪逆冲推覆构造形成于第四纪早期的西域砾岩沉积阶段，按距今2．5Ma计算，柯坪逆冲推覆构造的地壳缩短速率是15．4～17．3mm／a．Kalpin thrust tectonic is an active reverse fault fold zone at the southwestern Tianshan front piedmont, it consists of five to six rows of arc fold zones which are formed by Cambrian-Quaternary sedimentary rocks. The major morphology of the anticline is multiple box-shaped or asymmetry inclined, mostly, and it is similar to that of fault-bend fold and fault-propagation fold. Depending on the seismic reflection surveys data, the reverse faults on the front of the nappe in Kalpin thrust tectonic zone form an integrate detachment surface in the deep along the gypsum stratum in Cambrian. The depth of the detachment is shallower in the southeast and deeper in the northwest. The depth of the detachment fault is deeper in the west part （ about 9km deep） and shallower in the east part （about 5km deep） of the Piqiang fault. In the middle part of the Kalpin reverse fault-fold zone, we have made two balanced cross-sections at the two sides of Piqiang fault. On the two geological cross-sections, we construct the structure mode at depth using fault-bend fold or fault-propagation fold model. The length of the two sections is 73km and 78km, respectively. The restored sections yield a crustal shortening of 40km to 45kin, the shortening rate is 33% and 37% , respectively. Calculating the long-term shortening rate from these two across-sections is difficult, because the time of initiation of deformation is poorly known. Geological evidence suggests that most of the shortening began in the beginning of the deposition of the thick conglomerate unit in lower Quaternary. If the initiation time is about 2.5Ma, the shortening rate of Kalpin thrust tectonic zone is 15.4 - 17.3mm/a.

关 键 词：地壳缩短 逆冲推覆构造 柯坪塔格 天山 

分 类 号：P315.2[天文地球—地震学]