米苍山东河地质大剖面的构造几何学与运动学及其对上扬子北部陆内俯冲机制的约束

Geometry and kinematics model of Donghe geological cross section of Micangshan Mountain and constraint to the intracontinental subduction in the northern Yangtze

米苍山位于四川盆地北缘,受秦岭造山带由北向南挤压作用的影响,构造变形特征复杂,深入研究米苍山地区构造变形特征对陆内造山作用以及山前冲断带油气勘探具有积极作用。本文通过对米苍山地区的野外地质考察,对地表产状进行详细观测,建立了米苍山地区东河地表地质大剖面,并且利用等倾角区划与轴面分析,对东河剖面进行构造解析,建立了米苍山造山带构造几何学模型,通过构造楔模型分析了米苍山扇形隆升机制,通过不整合面分析,对四川盆地北部米苍山构造变形时间进行了研究。米苍山南缘基底发育4个构造楔,是影响米苍山南部地层抬升的主要原因,其顶部滑脱层为震旦系,底部滑脱层为元古界变质岩,前缘单斜带由嘉陵江—雷口坡组膏岩层作为滑脱层产生的反冲断层控制,寒武系滑脱层与震旦系滑脱层共同影响了大两会背斜的形成,而米苍山北缘则发育单个构造楔,其顶部滑脱层为震旦系,元古界变质岩为底部滑脱层;通过对米苍山地区不整合面研究,米苍山造山带自中生代以来,至少经历了印支期与燕山期两次大规模的隆升。因此,米苍山前表现为多期次多层滑脱的构造特征。

Micangshan Mountain located in the northern Sichuan Basin margin, it experienced compression driving force from north to south, which caused the structure much more complex in the front of Micangshan Mountain. We create East River cross section through collection of the strata attitude from field practice in the front of Micangshan Mountain, and do some structure analysis to the East River cross section using dip domain method and analysis of the axial surface, construct the geometry model of the structure in the front of the Micangshan Mountain, and finally, we use unconformity to analyze the structure evolution in the north Sichuan Basin. There lies four structure wedge underground in the front of the Mieangshan Mountain which are the main influence to the uplift of the Micangshan Mountain,and its upper detachment is Sinian,the Leikoupo Formation as detachment create recoil fault to control the formation of the monocline, the Cambrian detachment and the Sinian detachment both the deformation of Dalianghui Anticline. Through the analysis of the unconformity, Micangshan thrust belt has experienced two uplift events since Late Palaeozoic, therefore, it seems as the characteristic of multi-phase and muti-layer detachment in the front of Micangshan Mountain.