活动断裂带内第四纪松散沉积物的变形类型

DEFORMATION STYLES OF UNCONSOLIDATED QUATERNARY SEDIMENTS ON ACTIVE FAULTS

选择了一些典型活断层地质剖面 ,对经受了构造变动的第四纪松散沉积物进行了定向原状样品采集。通过室内样品固结、显微薄片制作和显微构造现象观察 ,从显微域里找到了第四纪松散沉积物变形的一些特点 ,并进行了分类。第四纪松散沉积物的变形类型有两种 :一种是破裂变形 ,主要表现为平行滑动条带、平直滑动界面、碎屑颗粒的破碎等 ;另一种是流动变形 ,主要表现为 :流动构造、碎砾旋转、粘土矿物的拖曳滑动等。

Unconsolidated Quaternary sediments are widely distributed on the Earth surface. As active faults usually disturb the Quaternary sediments, the study of the deformation styles of these sediments is therefore of great significance to the assessment of fault activity and property. Oriented samples of unconsolidated Quaternary sediments deformed by faulting have been collected from some typical active fault profiles. They were solidified in lab by filling epoxy resin diluted by acetone with solidified agent. Oriented thin sections were cut according to the primitive orientations of the samples in the field. Deformation features of the samples were observed carefully under optical microscope. An attempt has been made to identify the deformation microstructures of the samples, which may reflect the features of faulting. The observations show that the deformation in unconsolidated Quaternary sediments can be classified into two styles: fracturing and flow. The fracturing deformation is represented by parallel slip bands, straight slip planes, broken mineral grains etc, while the flow deformation is characterized by flow structures, mineral grain rotation, drag structure of clay minerals and others. The deformation style and property of unconsolidated Quaternary sediments depend to a large extent on the characteristics of the sediments themselves. Unconsolidated Quaternary sediments are composed mainly of clastic grains and clays. They can be considered as a visco-elastic body, and may behave as elastic-plastic materials. The duration of applied force has a great effect on the deformation behavior of unconsolidated Quaternary sediments. It means that strain rate plays an important role in the deformation behavior of unconsolidated Quaternary sediments. It is suggested that the fracturing deformation is generated by high strain rate event such as earthquake, while the flow deformation is generated by low strain rate event such as creep slip. The detailed observation of deformation styles of unconsolidated Quaternary sediments,therefore, may provide important information on the kinetic process of faulting.