| It is generally believed that sedimentary rocks have experienced six stages of rock strain and texture evolution,including depositional and diagenetic fabric,initial deformation fabric,pencil structure,initial cleavage,weak cleavage and strong cleavage,respectively,under the condition of parallel plane compression.Among them,the initial deformation fabric is generally believed to be formed after sedimentation and before consolidation diagenesis.And it records the paleo-stress information of basin-controlling structure and basin development period,which is the key to the analysis of tectonic attribute of sedimentary basin.However,the initial deformation fabric is often transformed during the later basin inversion deformation.Therefore,it is obvious that more case study is needed to further discuss the characteristics of rock fabric recorded by strata undergoing different degrees of deformation and modification,whether the original deformation fabric is retained and how it is superimposed by later deformation and modification.Moreover,the evolution of rock fabric in basins associated with extensional and strike-slip processes is not very clear.The fine-grained clastic rocks in the basin are also very sensitive to wispy stress changes.And it is important carriers for the study of rock fabric,especially the initial deformation fabric.In addition,the rock fabric of fine-grained clastic rocks is less affected by the paleocurrent direction,which is very helpful to distinguish the sedimentary fabric from the initial deformation fabric.So,it is very important to find out the development and evolution of rock fabric with fine-grained clastic rocks as the main research object.In this paper,we selected extensional basins of different periods and different deformations as the research objects,including Qinling orogenic belt(such as the Jurassic strata of Ciba Basin,the Cretaceous strata of Huicheng Basin and the Cenozoic strata of Lingbao Basin).We conducted the rock magnetism,as well as the room-and low-temperature magnetic fabric studies on fine-grained clastic rocks in the basin,and acquired the following insights:(1)The magnetic lineation of fine-grained clastic rocks in extensional basins which were developed in different periods and different deformation degrees from Mesozoic to Cenozoic intersects vertically or high angles with the extensional structures,such as normal faults and tensile joints.Besides,it also parallels to the extensional direction during the formation of basin.The magnetic foliation is parallel to the strata plane,which is the exhibiting characteristics of initial deformation fabrics.(2)The initial deformation fabric formed by the Mesozoic to Cenozoic fine-grained clastic rocks in the extensional tectonic setting can still retain the recorded stretching stress field during the early basin-forming.There is no obvious influence of tectonic activities such as compression folds during the basin inversion deformation.(3)The low temperature magnetic fabric can not only reflect the direction of tectonic stress field in the diagenesis process of fine-grained clastic rocks,but also improve the accuracy of the analysis of basin tectonic attribute via magnetic fabric. |
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