四川龙门山地区反转构造样式分析及其成因机制探讨

反转构造是当今构造地质学研究的新兴热点领域,本文尝试以反转构造和断层相关褶皱理论来探讨龙门山褶皱冲断带及川西前陆盆地中的反转构造样式及其成因。著者在综合前人研究成果的基础上,通过野外地质调查,室内构造分析与建模系统研究了龙门山地区典型的反转构造样式,讨论了龙门山带的反转性质,主干断裂的成因以及反转动力学机制。研究表明,龙门山的发育机制为一斜向正反转过程,区内发育有反转断层转折褶皱、被动陆缘型反转滑脱褶皱、反转断层传播褶皱以及受古生代裂谷控制的反转构造等反转构造类型;反转时期主要为印支期,本区在印支运动之前同时属被动陆缘和裂谷的构造背景;进入印支期后,受扬子陆块、华北陆块、羌塘陆块之间相互碰撞的影响而造山。该过程在本区不同地段表现存在差异,这种差异受控于前期的构造格局以及后期不同方向挤压应力的叠加。四川前陆盆地的发育和该过程有密切的联系,盆地内部具有裂谷构造反转的证据。

Analysis on the Patterns and Mechanism of Inversion Structures in Longmen Shan Region, Sichuan, China

The Longmen Shan,which lies along the eastern margin of the Tibetan Plateau,is one of the key regions concerning Mesozoic-Cenozoic tectonic evolution in China. The research of the Longmen Shan fold and thrust belt has a long history over half a century. Many achievements have been made on its structural features,evolution and mechanism. In recent years,as we put more emphasis on orogenic belts around the Tibetan Plateau and hydrocarbon exploration,many new methodologies,technology and thoughts have been applied to the research in this region. Inversion structure theory is a new spotlight in the structural geology studies. This article tries to use fold-related fold theories to discuss the patterns and mechanism of the inversion structures of the Longmen Shan fold and thrust belt and western Sichuan foreland basin. Research includes (1) Discuss the typical inversion structures (inversion fault bend folds,detachment folds,inversion fault propagation folds,and inversion structures controlled by the Paleozoic rifts) in the Longmen Shan region and its mechanism,integrating former achievements,seismic profiles,field investigation and structural analysis. (2) Build a three dimensional structural model of the Tangwangzhai Nappe to discuss its inversion process. (3) Use the fault-related folds theory to study the thin-skinned structural pattern in the western Sichuan foreland basin with emphasis on the inversion structures. (4) Discuss the origin of the three main faults and the dynamic process of the inversion. The research shows the Longmen Shan region experienced an oblique inversion process in early Mesozoic. The tectonic setting before the inversion is a combination of passive continental margin and intra-continental rifting. The inversion process varies along trends,which is caused by differential combination of N-S compression from Qinling and W-E compression from the Songpan-Ganzi Terrane. These variations are also controlled by preexisted inhomogeneous structures in the autochthon,including crystalline basement and Paleozoic and Early Mesozoic extensional structures. Based on deep seismic profiles and petrology evidence,the Longmen Shan may also be originated from an aulacogen.