Sedimentary Responses to Late Cenozoic Thrusting and Strikeslipping of Longmen Shan along Eastern Margin of Tibetan Plateau
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摘要: 成都盆地位于青藏高原东缘，夹于龙门山与龙泉山之间，盆地的长轴方向平行于龙门山，呈现为北东—南西向展布的线性盆地。盆地中充填了3.6Ma以来的半固结—松散堆积物，最大厚度为541 m，在垂向上由下部的大邑砾岩、中部的雅安砾石层和上部的上更新统至全新统砾石层组成，其与下覆地层均为不整合接触，显示该盆地是一个单独的成盆期,并非是在中生代前陆盆地基础上形成的继承性盆地。在垂直于龙门山造山带方向上，成都盆地具不对称的楔形结构,沉积基底面整体向西呈阶梯状倾斜，盆地中充填的碎屑物质均来源于盆地西侧的龙门山，具横向水系和单向充填的特征；而且盆地的沉降中心具有逐渐向远离造山带方向迁移的特征，显示盆地的挤压方向垂直于龙门山主断裂，造成了成都盆地在垂直于造山带方向上的构造缩短。在平行于龙门山造山带方向上，成都盆地具有一系列的北东向延伸的次级凸起和凹陷，凹陷和凸起相间分布，且在空间上呈斜列形式展布于盆地的底部，其中次级凹陷（沉降中心）和冲积扇具有向平行龙门山造山带方向迁移的特征，表明成都盆地西缘的龙门山断裂具有右旋走滑的特征。鉴于以上特征，认为成都盆地是在龙门山造山带晚新生代走滑与逆冲的联合作用下形成的走滑挤压盆地。Abstract: Chengdu basin developed ahead of Longmen Shan along the eastern margin of Tibetan Plateau, lying between the Longmen Shan and Longquan Shan, and extends from southwest to northeast with the long axis of the basin parallel to Longmen Shan. The filling in the basin with a maximum thickness of 541m include Dayi conglomerate, Yaan gravel layer and Late Pleistocene and Holocene gravel layer. In the transverse section of the basin(vertical to Longmen Shan), the wedge shaped sediments in the basin were derived from Longmen Shan and gradually northwestwards thickening, the depocenter is located in the northwestern part of the basin. As thrusting progressed southeastwards, the northwestern margin and the depocenter of the basin had been progressively migrated southeastwards. According to this evidence, it can be inferred that the direction of trusting and tectonic shorting was from NWSE and vertical to Longmen Shan. In the longitudinal section (parallel to Longmen Shan), there are many minor echelon depressions and uplifts, as dextral strikeslipping progressed northeastwards, the minor depression (rhombocham) and fan had been progressively migrated northeastwards. According to these lines of evidence, we can infer that the direction of dextral strikeslipping was from SWNE and parallel to Longmen Shan. So we draw a conclusion that the Chengdu basin is one of typical transpressional basin controlled by thrusting and strikeslipping along Longmen Shan since 3.6Ma.
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