四川盆地成盆前地质结构及其向盆地转化

PRE-BASINING CONSTRUCTION OF SICHUAN BASIN AND ITS TRANSFORMATION

韩永辉 郭正吾

Han Yonghui Guo Zhengwu

地质矿产部西南石油地质局

Southwest China Bureau of Petroleum Geology, Ministry of Geology and Mineral Resources

上扬子地台周边出露的前震旦纪地层是崆岭群、大别群和黄水河群下伏的条带状混合岩系。它们呈东西向展布在北纬30°—32°之间。航磁资料是一个东西向展布的强磁异常带,为组成基底的基性—超基性岩体的反映。从江汉到四川为基性—超基性岩及其间的最老沉积物构成的一套地层,它们于17—19亿年经变质作用、混合岩化和花岗岩化作用固结并转为陆壳。在其北侧平行分布一个冒地槽和一个优地槽,晋宁运动使其关闭,形成陆壳,镶嵌于四川—江汉陆壳区的北缘。在其南侧广大地区四堡期为洋壳上的优地槽沉积,四堡运动(14亿年)强烈褶皱固结并使具过渡性地壳性质;晋宁期为以板溪群为代表的冒地槽沉积,并超复到川东及江汉地区,晋宁运动在康滇一带形成许多中酸性杂岩体,使其基底不均一,澂江运动则对晋宁运动已基本固结定形的上扬子地台基底进行局部改造(图1)。

By reviewing comprehensive geological data from Sichuan basin and adjacent areasopre-basining construction and main factors affecting them are studied. In the light of opening and closing of the ancient Tethys in China, the mechanism of formation and transformation of the basin is discussed and four relavant stages are identified as follows. 1) Stage of formation of the basement (pre-Sinian), when the basement was consolodated and turned into continental crust through pre-Sibao orogeny (1.700m.y. -1.900m.y.),Sibao orogeny (1.400m.y.) and Jinning movement (800m.y.). 2) Stage of uplifting of Chuanzhong-Kangdian-Yajiang crustal rise (pre-Permian) which, according to depositional characteristics, thicknesses, bio-assemblages and tectonic features of strata from Sinian to Carboniferous, is believed to be the westerly extention of Upper Yangtze plateform. 3) Stage of initiation of basinning (Permian to Middle Triassic), represented by disintegration of the thermogenic tectonic rise proposed above, the opening of the north branch of the ancient Tethys, the reversion of regional stress field (from compressional to tentional) and the variation of thermo-regime, all of which influenced the Chuanzhong rise in such a Way that denudation there was converted into subsidence, resulting in initiation of formation and evolution of the basin. 4) Stage of formation and evolution of the basin (Late Triassic), when predominant controlling factors for the basinning were the opening and closing of the ancient Tethys. Moreover, influences of other factors and margins on the evolution of the basin elsewhere are briefly described, characteristics of the basin during each stage and mechanism of subsidence are discussed and, subsequently, three promising prospects for petroleum are recommended.

https://doi.org/10.11781/sysydz198404288