远安地堑碎裂带的微观特征及其形变机制

Micro-characteristics and deformation mechanism of cataclastic band in Yuan’an Graben

以远安地堑红花套组岩屑质石英砂岩中发育的碎裂带为例,在详细研究其宏观特点的基础上,结合室内分析资料,重点描述碎裂带的微观特征,并对其形变机制进行深度剖析与探讨。结果表明,研究区变形带具有浅埋藏-中埋藏深度的特点,主要发育碎裂带。最常见的颗粒破碎方式为多点接触破裂以及完全碎裂。微观特征表现为单条碎裂带顺其延伸方向形变不均一、单条碎裂带内部垂直于其延伸方向形变相对均一、由强烈的碎裂流作用导致的碎裂带强化、簇状碎裂带内部结构不均一等,以上反映了碎裂变形带的形成过程,也指示其形变机制由碎裂作用向碎裂流作用转变。变形带的时间演化序列为碎裂核形成-中等碎裂程度型碎裂带-完全碎裂型碎裂带-簇状碎裂带,最终可能会沿某条碎裂带形成滑动面。野外常见中等碎裂型簇状碎裂带以及完全碎裂型簇状碎裂带,完全碎裂型簇状碎裂带内孔隙度和渗透率与母岩相比减小严重,实测可降低4个数量级,很可能会对流体渗流产生较大影响。

Aiming at the cataclastic band developed in lithic quartz sandstone of K2h Formation in Yuan’an Graben,based on the detailed study of its macro-characteristics and experimental analysis data,the micro-characteristics of the cataclastic band are described,and the deformation mechanism is analyzed and discussed in detail.The results show that the deformation band in the study area has the characteristics of shallow to middle burial depth,in which cataclastic band is mainly developed.The most common modes of grain breakage are multi-point contact and complete fragmentation.The micro-heterogeneity is characterized by the inhomogeneous deformation of a single cataclastic band along its strike,the relatively homogeneousdeformation of a single cataclastic band perpendicular to its strike,the strengthening of the cataclastic band caused by the strong cataclastic flow and the inhomogeneous inner-structure of the cataclastic bandclusters,which reflects the formation of the cataclastic deformation band,and also indicates that its deformation mechanism changes from cataclasis to cataclastic flow.The temporal sequence of the deformation zone is from the cataclastic core formation to medium-degree fragmented cataclastic band to cataclastic band with complete crushed grains to cataclastic band clusters.Finally,a sliding surface may be formed along a certain cataclastic band.In the field,it is common to find the medium-degree fragmented cataclastic band clusters and completely crushed deformation band clusters.Compared with the host rock,the porosity and permeability in the completely crushed deformation band clusters are seriously decreased,which can be reduced by 4 orders of magnitude in actual measurement,and it is likely to have a great impact on fluid flow.