Main characteristics and structural evolution of the Tumxuk fault zone in the western Tarim Basin
Zhu Defeng1, Liu Hefu2, Wu Genyao3
1. Exploration and Development Research Institute of Daqing Oilfield Company Ltd., Daqing, Heilongjiang 163712; 2. School of Energy Resources, China University of Geosciences, Beijing 100083; 3. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029
The Tumxuk fault zone in the western Tarim Basin is a boundary between the Bachu Fault-Uplift,a sub-order unit of the Central Rise whose predecessor was a Jinningian collisional orogen,and the Awat Sag(sub-order unit of the North Depression). A lot of geological and geophysical data demonstrated that the Tumxuk fault zone,with a very complicated internal structures,was a deep fracture cutting across the crust. To combine the regional tectonic evolution,the structural development of the fault was reconstructed,which showed three generations of thrusting once occurred during geohistory. The Caledonian thrusting in the latest Ordovician was more violent in the W-E-striking segment of the fault,with the Bachu Fault-Uplift obducted north(east)wards onto the Awat Sag,and the NW-striking structure might be a neogenic one during that time. The igneous activity along the fault recorded rifting occurred in Early-Middle Permian,then it inverted and thrust by the end of Middle Permian. The fault zone acted as a demarcation line between the depressing and uplifting regions in Juro-Cretaceous. The Neogene thrusting could be divided into two epochs. The Miocene thrusting,with the Bachu Fault-Uplift obducted southwards onto the Markit Slop,attached to southward expand of the South Tianshan foreland fold-and-thrust belt,while the Pleistocene one,with the Bachu Fault-Uplift obducted north(east)wards onto the Awat Sag,attached to northeastward expand of the West Kunlun foreland fold-and-thrust belt. The NW-striking segment showed a stronger deformation in the Pleistocene thrusting,indicated a closer relation to the West Kunlun intracontinental orogeny. The segmentation of the Tumxuk fault zone resulted mainly from development of the fault itself: the NW-striking segment,as a neogenic structure,enhanced successively in the Hercynian and Himalayan orogenies,especially in Pleistocene.