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    中生代多向挤压构造作用与四川盆地的形成和改造

    Mesozoic multi-directional compressional tectonics and formation-reformation of Sichuan basin

    • 摘要: 提要:远离活动板块边缘的四川盆地以其周缘复杂分布的褶皱构造带而著称,这些构造带的成因及其大地构造背景一直是华南大地构造研究的焦点之一。本文基于区域构造编图、褶皱构造样式和叠加变形分析,论述了四川盆地及其周缘中生代挤压变形特征及其定型时代,确定了重要构造事件及其产生的构造样式。研究显示,四川盆地及其周缘地带中生代经历了3个重大构造事件,每个构造事件产生的构造形迹在空间上发生复合和联合,造就了四川盆地及其周缘复杂的构造组合样式。中晚三叠世碰撞造山事件(印支运动)在扬子地区形成近W-E向褶皱构造,扬子地块西缘伴随着松潘—甘孜褶皱造山带的形成,发育了龙门山—锦屏山逆冲-推覆构造带及川滇前陆盆地,奠定了川—渝—黔—滇大型沉积盆地,构成四川盆地的原形。中晚侏罗世时期(燕山早幕),东亚构造体制发生重大变革,来自北部、东部、西部和南部的板块多向汇聚导致了大陆多向汇聚构造体系的形成和发展,其中秦岭造山带的再生活动导致南部米仓山—大巴山前陆构造带的形成和发展;来自太平洋板块向西推挤,导致了川东地区NW向突出的弧型构造和川南华蓥山帚状构造的形成;羌塘地块的向东侧向挤出,在扬子地块西北缘发生褶皱逆冲变形(龙门山—锦屏山构造带)。这期多向挤压事件强烈改造了四川T3-J1-2原形盆地,周缘褶皱构造带基本定型。早白垩世晚期的挤压事件(燕山晚幕)进一步改造了四川盆地,NW-SE向构造得到加强。除了西缘以外,四川盆地其他周缘褶皱构造带主体定型于晚侏罗世的陆内造山作用阶段,是扬子克拉通周边造山带在周邻板块多向汇聚作用下引发的再生复活的结果,成为中国东部陆内汇聚构造体系的重要组成部分。

       

      Abstract: Abstract:The Sichuan basin located far away from the active plate boundaries is well known for its surrounding fold zones whose genesis and tectonic settings have long been one of the key issues in the geotectonic study of South China. Based on a compilation of regional structural geology and an analysis of superimposed folding structures, this paper presents a synthetic discussion on the Mesozoic compressional tectonics in such aspects as its deformation features and structural styles, main tectonic events and their timing. Strudies show that the Sichuan basin and its surrounding zones experienced three major tectonic events during Mesozoic, each one creating fold zones that were compounded spatially and resulted in the formation and reformation of the Sichuan basin. The Triassic collisional orogeny along the northern and western margins of the Yangtze cratonic block resulted in the formation of the proto basin, i.e., the Chuan-Yu-Dian -Qian sedimentary basin whose extending size is larger than the present-day Sichuan basin. Folds created by this tectonic event mainly trend in W-E direction. Tectonic regime changed profoundly during the Middle-Late Jurassic, dominated by multi-directional plate convergences in Asia, which caused rejuvenation of old orogenic belts and formation of new tectonic systems. In particular, the rejuvenation of the Qinling orogenic belt resulted in the development of the Micangsahn-Dabashan foreland fold and fault zone along the northern margin of the Sichuan basin; the westward subduction of the Paleo-Pacific plate activated the Xuefengshan tectonic zone and created the oroclinal folds in east and south Sichuan; the eastward extrusion of the Songpan-Ganze orogenic belt reactivated the Longmenshan-Jinpingshan thrust zone in west Sichuan. This multi-directional compressional event greatly reformed the proto Sichuan basin, and shaped the basic structural pattern surrounding the Sichuan basin. The third major event occurred in latest Cretaceous and was characterized by NW-SE compression, and it strengthened the NE-SW trending structures. It is concluded that the main fold zones in and around the Sichuan basin was characterized by pervasively distributed thin-skinned structures mainly formed in Middle-Late Jurassic, and in consequence of multi-directional intracontinental orogeny, they constituted in turn part of the convergent tectonic system in east Asia.

       

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