【作者】 郭秀峰；

【导师】 张国伟；

【作者基本信息】 西北大学 ， 构造地质学， 2009， 硕士

【摘要】 秦岭造山带南部南大巴山弧形推覆带前缘的前陆褶皱带西缘与米仓山东西向构造东端形成了镇巴—简池以北的横跨叠加区和南部以出露三叠系与侏罗系为主的扇形三角叠加区。研究不同类型叠加区构造几何学和运动学特征及其形成演化,有利于更好地认识燕山期以来秦岭造山带与扬子地块北缘陆内构造的关系。以前人研究成果为基础,论文利用野外构造观测和褶皱几何要素统计进行构造解析,辅以磁组构测试方法,结合地球物理解释资料,综合分析了印支期勉略带闭合后燕山期为主的陆内构造演化过程南大巴山推覆带西缘与米仓山近东西向短轴背斜、米仓山南部巨型挠曲向斜的叠加关系。经分析总结最终得出以下认识与成果:(1)初步探讨了研究区扇形三角叠加区的形成机制。米仓山南缘近东西向挠曲向斜与华蓥山西缘向斜在研究区南部镇巴—万源之间叠加形成一个北东收敛、南西开放的向斜叠加区;稍后南大巴山前陆褶皱带南西向的推覆叠加,使这一区域形成现今以三叠系—侏罗系为主要变形岩层的扇形三角叠加区构造面貌。(2)基于前人成果和本文取得认识,探讨了四川盆地东北缘研究区范围内燕山期陆内构造的演化时序。中侏罗世末扬子地块向北的继续深俯冲在其北缘首先发育一期近东西向褶皱构造,近于同时或稍晚川东褶皱带由南东向北西扩展,与米仓山南缘的东西向挠曲向斜形成叠加向斜;晚侏罗世末,大巴山构造带在两侧汉南和黄陵刚性地块的阻挡下向南西方向推覆,形成了指向南西的弧形南大巴山前陆褶皱带,与上述向斜叠加,这一由三方向构造共同作用下的叠加过程至少持续到早白垩世晚期,其中米仓山近南北向挤压则趋于减弱。(3)对磁组构在多方向多期次水平挤压形成叠加变形的沉积岩区的应用进行了探索性的尝试。论文研究取得一些初步认识与成果,同时还提出应用其进行叠加构造分析时必须与区域地质资料紧密联系,并应在一定限定条件下使用。更多还原

【Abstract】 In the front of south Dabashan arcuate thrust belt, two kinds of superposed areas are formed in the west margin of foreland fold belt, the one is the cross superposed area in the northern part, and the other is a fan-shaped superposed area, which is dominated by Triassic and Jurassic in the southern part. It is meaningful to study the structural geometry and kinematic characters and formation of different types of superposed areas to further understand the intracontinental tectonics and relationship between the Qinling orogenic belt and the north margin of Yangtze block. Based on previous research results, some research methods are applied in this study, such as structural analysis by field observation and statistic of fold geometric factors, test of anisotropy of magnetic susceptibility（AMS） and so on. The discussion comprehensively analysis the superposed relationship between the west margin of south Dabashan foreland fold belt and the Micangshan nearly EW anticline, as well as the giant flexural syncline located to the south of the Mt. Micangshan during the Yanshanian intracontinental tectonic evolution after the closure of Mianlue suture in Indosinian. The most significant fruits of this study can be concluded as follows.1) The formation mechanism of the fan-shaped superposed area is preliminarily discussed. At the first step, the nearly EW giant flexural syncline to the south of Mt. Micangshan and the NNE syncline to the west of Mt. Huayingshan were superposed in the south of the study area and a broad superposed syncline area was formed, whose NE part was narrow while SW part was raletively wide. Later, the broad syncline underwent another superposition by the west margin of south Dabashan foreland fold belt, and the fan-shaped superposed area which mainly outcrop Triassic and Jurassic was finally formed at the south of study area.2) Based on previous results and boundaries of abundant materials obtained in this study, it can be inferred that the NE margin of Sichuan basin has undergone the following intracontinental tectonic evolution sequence in Yanshanian. Late J₂, a nearly EW fold was formed in the north margin of Yangtze block, due to the continuing subduction of Yangtze block towards north. Synchronously or later, the South Sichuan fold belt extended from SE to NW, and superposed with the nearly EW flexure syncline and formed the primary framework of the south part of study area. Because of the barrier of Hannan and Huangling rigid blocks, at late J3, the Dabashan thrust belt overthrusted from NE towards SW, which induced the foreland fold belt and superposed onto the former syncline. Furthermore, the tectonic regime made up of the three different tectonic stress last to at least late of K₁, however, the nearly SN compressional stress became much weaker in the late stage.3) Due to the study and analysis of the application of magnetic fabric in such a condition where the sedimentary rocks deformed in a multi-stage and multi-direction regime, plenty of useful information are obtained, and it’s also suggest that this method should be based on the basic geologic background and be used carefully in intricate area.更多还原