A study on the evolutionary process of a large-scale strike-slip fault

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The evolutionary process of a fault includes several stages, starting from a set of fractures in intact rocks, through a somewhat integrated zone of fractures and minor faults, finally to a single strand of matured fault. This process has been studied by comparing different faults at different evolutionary. Because the faults used in these studies have different tectonic setting, it was difficult to differentiate the evolutionary process from variation in tectonic setting. In this study, we tried to clarify the process through a study of the Kanding-Xianshuihe-Xiaojiang Fault Zone (KXXFZ) in southeastern Tibetan Plateau.A big bend exists in the middle portion of this fault zone. The Dalianshan Fault Zone (DFZ) develops east of, and shortcutting, this big bend. We made precise mapping and field observations of tectonic landforms. The following results were obtained:1. The total amount of slip on DFZ is found to be 3-7 km, which is one order of magnitude smaller than that on KXXFZ. The slip rate on DFZ in Holocene time is estimated at 4 mm/yr or more. These imply that the initiation of DFZ is younger than 1-2 Ma, which again is one order of magnitude younger than KXXFZ.2. The DFZ consists of many fault strands that are arranged en echelon ; the sheared zone of each fault strand is much narrower than that associated with the main fault zone. This, coupled with the above observations, indicates that the Dalianshan Fault Zone is at the juvenile stage of a fault with less integrated fault strands.3. The DFZ develop in a Precambrian platform without any signs of inheritance from preexisting structures. It is therefore inferred that, in association with the formation of a big bend, a new fault was created in intact continental crust in recent geologic time, shortcutting the big bend.