GENESIS OF X-SHAPE STRIKE-SLIP FAULT SYSTEM IN INTRACRATON-TAKING THE NORTHERN TABEI UPLIFT OF THE TARIM BASIN AS AN EXAMPLE

Unlike the typical large-scale, long-displacement strike-slip faults under the simple-shear mechanism, the northern Tabei uplift of the Tarim Basin develops X-shape strike-slip fault system with characteristics of long, small-scale, and short-displacement. Restricted by sedimentary surface, the X-shape strike-slip faults show three levels of flower structure in Cambrian-Ordovician, Silurian to Permian, and Trassic to Palaogene in profile, indicating 3 periods of fault action.

There are many researches on the genesis of X-shape strike-slip fault system, but there are few simulation on their initiate, propagate and evolution. It controls the development and distribution of oil and gas reservoirs. So, it is of great significance to study on its genesis and evolution. In this paper, based on geometry and kinematics study, it is concluded that the compression from south to north caused by the subduction of the Late Ordovician Paleo-Kunlun Ocean and the Paleo-Altyn Ocean make the X-shape strike-slip fault be initiated. Based on this tectonic background and constrainted by the shortening obtained by back stripping to add the velocity boundary condition, the 3-Dimension Distinct Element Code (3DEC) is used to simulate the initiation of X-shape strike-slip faults. The results show that several groups of NE and NW trending faults first appear in the south area and extend from south to north. Then the two groups of faults intersect to form X-shape faults, and they further develop northward, and finally forms a X-shape strike-slip fault system in plane of Cambrian-Ordovician strata. In the Late Hercynian, the closure of the South Tianshan Ocean led to the southward compression of the continental- continental collisional orogeny, and the X-shape strike-slip faults continued to develop in the north. During the Early Himalayan period, the Indo-European plate collided, the fault acted again, and only the dextral strike-slip displacement occurred, resulting in the NE trending echelon normal fault. Therefore, X-shape strike-slip fault of intracraton in Tarim Basin is a type of strike slip fault corelated with Anderson Model. And the long distance of the fault reveal that they are “growth faults” results from the undergoing of Caledonian compression by subduction of paleo-Kunlun Ocean and the Paleo-Altyn Ocean.