The Deep Structurs which are Transformed From Strike-slip ones into extending ones and Their Composite evolution of The Southern Segment of Tanlu Fault Belt During Yanshanian stage

The Tan-Lu fault is a well-known active fault belt in eastern Asia. After 40 years of study, a series of important scientific results have been achieved. However, its deep structure, activity history and mechanism still remains in debate. A large quantity of geophysical exploration work has been conducted since late 1990's. This paper focuses on the Jiashan- Lujiang section based on the geophysical exploration, magnetotelluric and magnetic sounding and seismic survey. We find the southern part of the Tan-Lu fault belt can be separated into two parts with different characteristics along the Chihe-Taihu sub-fault. In the east, the Tan-Lu fault belt is composed of several sub-faults with a positive flower structure, characterized by strike-slip in the late Middle Jurassic to early Late Jurassic. In the west, the Tan-Lu fault belt is represented by extensional fracture, made of 3 sub-faults near Dingyuan county. Among them, two sub-faults stretch to the south disappearing in the Hefei basin, one sub-fault, i.e., the Chihe-Taihu sub-fault stretches to the east edge of the Hefei basin, showing a half-graben structure with fault depression occurred in the Early Cretaceous. we establish the evolution model in the Jiashan-Lujiang section with active transforming from strike-slip to extension as well as its relationship between adjacent regions.Our study can be better integration of geological phenomena, interpreting the different views.Our model presents more reasonable explanation for the proposed different points of view on "rift valley hypothesis" and "strike-slip hypothesis". It provides new concept for the further study of the Tan-Lu fault belt.