孟加拉湾若开盆地构造特征及演化

摘要

This paper analyzes the structural characteristics and tectonic evolution of Rakhine Basin based on 2D seismic data and well data.The basin is located at accretionary wedge with a trench setting of active continental margin and has experienced the embryonic stage (Late CretaceousPaleocene),collision stage (Eocene-Oligocene) and quick collision stage (Miocene-Pliocene).Rakhine Basin can be subdivided into the submarine plain in the west and the Rakhine fold belt in the east.The Rakhine fold belt consists of the northern compressive fold belt and the southern strike-slip fault belt.In the northern compressive fold belt develop a lot of NNW-trending linear folds that can be subdivided into steep folds with high amplitude caused by the intensive tectonic deformation from east to west.In the southern strike-slip fault belt,some anticlines form along the strike-slip fault and the unambiguous flower structures.The evolution of the regional section suggests that the deformation began at the end of Late Miocene,and became intensive from the end of Pliocene to Quaternary.The structures in the east are older and more intensive than that of the west due to the regional contraction from east to west and the deformational propagation westward.The deposition center migrated from east to west after Miocene formation deposited.All the characteristics of Rakhine Basin are mainly controlled by different stress patterns caused by the subduction formed between the Indian-Australia plate and the Eurasia plate.%根据地震、钻井等基础资料建立主干剖面,结合平面构造展布及剖面构造特征研究孟加拉湾若开盆地的构造特征和演化.若开盆地是一个主动大陆边缘海沟背景下的增生楔盆地,经历了晚白垩世-古新世早期发育期、始新世-渐新世缓慢碰撞期和中新世-上新世盆地定型期3个区域演化阶段.平面上划分为东部的若开褶皱带和西部的海底平原带.若开褶皱带具有南北分段特征,根据构造特征差异分为2段:(1)北段挤压褶皱带,主要发育NNW走向、带状分布褶皱.北段挤压褶皱带可分为高陡褶皱带和低缓褶皱带2个次一级构造单元,变形强度从东往西逐渐减弱.(2)南段走滑褶皱带,褶皱表现为宽度较窄,并发育明显走滑构造.主干剖面构造演化史分析认为:研究区构造变形开始于晚中新世末,上新世末-第四纪变形强烈;构造变形从东向西传播,东部变形时间早,变形强烈,而西部变形时间晚,变形较弱;在中斯统沉积后,区域构造发生翘板式逆时针旋转,沉积中心从东部迁移到西部.若开盆地的构造形成与演化主要受印度板块向欧亚板块斜向B型俯冲碰撞控制,由于俯冲碰撞接触带在若开盆地呈弧状,南北两段应力场不同,导致南北两段构造变形存在明显差异.