川西盆地晚三叠世沉积特征及原型盆地分析

发布时间：2019-05-29 16:05

【摘要】：川西盆地位于扬子板块西缘,现今东以龙泉山隆起与川中地区分隔,西以龙门山北川-映秀断层为边界。中三叠以前,川西盆地作为扬子板块被动大陆边缘沉积了巨厚的海相碳酸盐岩地层。自晚三叠世以来,伴随印支运动,川西盆地逐渐过渡为陆相沉积盆地,沉积马鞍塘组和须家河组。从现今构造格架分析,龙门山逆冲构造带、川西盆地与龙泉山隆起均呈NE走向,似乎具有盆-山配套关系,因此晚三叠世的川西盆地长期被认为是现今龙门山逆冲推覆带控制形成的前陆盆地,以须家河组(T3x)为代表的晚三叠世沉积为前陆盆地沉积。然而在川西盆地发育的上三叠统在盆地的西南段明显为北川-映秀断层截切,在断层西侧上盘仍发育有须家河组等地层,位于龙门山腹陆带内的探井也钻遇须家河组,表明晚三叠世盆地西缘并非现今的北川-映秀断层。因此,重建晚三叠世川西原型盆地是深入理解这一时期盆地-山脉关系,乃至重新认识川西地区晚三叠世构造格局的关键。原型盆地分析的关键是盆地沉积物的特征,我们综合研究了川西盆地野外露头资料及钻井资料,分析上三叠统的沉积特征及展布特点。结果表明从早到晚须家河组沉降中心具有从北东向南西迁移的规律,其中的砾岩沉积物从T3x2~T3x4分布范围逐渐扩大,具有从盆地北段向中段进积的规律。运用碎屑锆石测年方法,分析确定须家河组初始沉积年龄为222Ma,碎屑锆石指示其物源主要来自西秦岭。综合分析以上成果,表明晚三叠世从早到晚以粗碎屑为代表的盆地边缘相和盆地沉降中心从北向南西迁移,边缘沉积相带走向可能从近东西向逐渐转变为NE向,从而在此基础上建立了晚三叠世川西盆地演化模式,认为其主要受西秦岭南缘逐渐向南西扩展的前陆逆冲构造控制。
[Abstract]:The western Sichuan basin is located in the western margin of the Yangtze plate. At present, the Longquan Mountain uplift is separated from the central Sichuan area in the east, and the Beichuan-Yingxiu fault in the west is the boundary in the west. Before the Middle Triassic, the western Sichuan Basin, as the passive continental margin of the Yangtze plate, deposited a very thick marine carbonate strata. Since the late Triassic, with the Indochina movement, the western Sichuan basin has gradually transitioned into a continental sedimentary basin, sedimentary Maantang formation and Xujiahe formation. From the analysis of the present tectonic framework, the Longmenshan thrust tectonic belt, the western Sichuan basin and the Longquanshan uplift show NE strike, which seems to have a basin-mountain matching relationship. Therefore, the western Sichuan basin in the late Triassic has long been considered to be a Foreland basin controlled by the Longmenshan thrust nappe belt, and the late Triassic deposits represented by the Xujiahe formation (T3x) are the Foreland basin deposits. However, the Upper Triassic developed in the western Sichuan basin is obviously cut by Beichuan-Yingxiu fault in the southwest section of the basin, and there are still Xujiahe formation and other strata in the upper plate on the west side of the fault, and the exploration wells located in the Longmenshan ventral continental belt are also drilled into the Xujiahe formation. It shows that the western margin of the late Triassic basin is not the present Beichuan-Yingxiu fault. Therefore, the reconstruction of the late Triassic prototype basin in western Sichuan is the key to deeply understand the basin-mountain relationship in this period, and even to re-understand the late Triassic tectonic pattern in western Sichuan. The key to the analysis of the prototype basin is the characteristics of basin sediments. We comprehensively study the outcrop data and drilling data in the western Sichuan basin, and analyze the sedimentary characteristics and distribution characteristics of the Upper Triassic. The results show that the subsidence center of Xujiahe formation has the law of migration from north east to south west from morning to night, and the distribution range of gravel sediments is gradually expanded from T3x2~T3x4, and it has the regularity of accumulation from the north section of the basin to the middle part of the basin. By using the clastic zircon dating method, it is determined that the initial sedimentary age of Xujiahe formation is 222 Ma, and the clastic zircon indicates that its provenance mainly comes from the West Qinling Mountains. The comprehensive analysis of the above results shows that the basin margin facies and basin subsidence center represented by crude clastic migrated from north to south and the marginal sedimentary facies belt may gradually change from near east to west to NE from early to late Triassic. On this basis, the evolution model of the late Triassic western Sichuan basin is established, and it is considered that it is mainly controlled by the Foreland thrust structure which gradually extends to the south west of the southern margin of the western Qinling Mountains.
【学位授予单位】：中国地质大学(北京)
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：P534.51

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