弥散性走滑条件下底辟构造特征研究:以莺歌海盆地为例

实验以莺歌海底辟构造为典型实例设计3组砂箱物理模型,探讨弧形弥散性基底走滑与上覆同构造沉积对底辟构造样式及演化过程的影响。砂箱物理模拟表明:物质变形主要集中在弥散性剪切带内、且断裂特征与底辟带形成演化具有一定耦合性。底辟带断裂欠发育、以塑性应变为主,仅在底辟翼部和顶部分别形成小型逆冲断层和放射状裂隙;但底辟带外缘普遍发育高角度弥散性走滑断裂体系。沿弧形走滑剪切方向,底辟物质斜向生长由倾向外弧逐渐转变为倾向内弧,导致其平面上为非对称结构形态。同构造沉积地层与底辟相互作用控制了底辟生长结构及上覆地层的变形,底辟通过逐渐减小刺穿以响应上覆沉积载荷的增加。基于比例模型模拟结果与莺歌海盆地典型底辟带构造特征具有一定相似性,揭示出莺歌海盆地底辟构造及分布特征受红河断裂带弥散性走滑与同构造沉积过程共同控制。

STRUCTURAL CHARACTERISTICS OF DIAPIR STRUCTURE UNDER DISTRIBUTED STRIKE-SLIP:A CASE STUDY ON YINGGEHAI BASIN

Three sets of models were designed and restricted with the typical examples of mud-fluid diapirs in Yinggehai Basin so as to discuss the effect of distributed shear and syntectonic sedimentation on the evolution process of structural style of diapir structures.The experiments indicate that the deformation mainly concentrated in the distributed shear zone and the characteristics of fault system was correspondent to the evolution of the diapir zone.There were many high angle strike-slip faults outside the diapiric zone,while in the diapiric zone,there were only some small thrust faults along the diapiric margin and radial fractures on the top of the diapir.Along the shear direction,the flow direction of diapired materials gradually changed from dipping toward outer arc to inner arc and formed an asymmetric shape in plane.The interaction between syntectonic sedimentary deposition and diapirism controlled the growing structure of diapir and the deformation of overlying layers.On the top of diapir structure,it became smaller in responding to the increase of overlying sedimentary loading.The results of scaled analogue experiments conducted are similar to the typical diapiric zone in Yinggehai Basin.It is considered that the diapir structural style and the distribution in Yinggehai Basin are controlled by both distributed strike-slip movement of the Red River fault zone and syntetonic sedimentary process.