Active modes and mechanisms of the Paleozoic faultings in western Tarim
Li Yuejun1, Wu Genyao1, Meng Qinglong1, Shi Jun2, Feng Xiaojun2, Zheng Min3
1. Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029; 2. Tarim Oilfield Branch Company, China National Petroleum Corp., Korla, Xinjiang 841000; 3. Lanzhou Oil-Gas Resource Centre, Institute of Geology and Geophysics, Chiinese Academy of Sciences, Lanzhou 730000
Based on systematic interpretation of seismic profiles and a comparative study to central area of the Tarim Basin,the active modes and mechanisms of the Paleozoic faultings in western Tarim were explored in the paper.The NE-striking Madong (Badongnan) fault zone,as a part of southeastern boundary of the Bachu Fault-Uplift,was a superficial d閏ollement fold-and-thrust belt,and expanded southeastwards.The piggy-back thrusting occurred in the end of Ordovician.The NW-striking Badong fracture (or the No.2 Tumxuk fracture),the eastern boundary of the Bachu Fault-Uplift,was a basement-involved thrust,with the thrusting occurring in the ends of Ordovician and Middle Permian respectively.The Baxi and South of Well Tacan 2 fractures in north part of the Markit Slope were Hercynian normal faults.The Paleozoic development of the Tarim paleo-plate was constrained by the neighbouring orogenic evolution.The thrusting of nearly W-E and NE-striking fractures in early Caledonian,related to subduction of the West Kunlun ocean,might inherit the basement structures.The NW-striking fractures in central Tarim was neogenic in Late Cambrian,in which two episodes of Caledonian deformation could be recognized: the early thrusting in the end of Ordovician and late thrusting and strike-slipping during Late Silurian to Middle Devonian.The later deformation should be resulted from the activation of the Paleo-Altun shearing orogen,so as to obviously become weeker westwards.Some NW-striking fractures in west Tarim,for example,the Kangxi fracture,attached to the Tazhong (central Tarim) NW-striking fracture system.The NE-striking Madong fault zone was a transfer fault between the Tumxuk fault zone (thrusting towards the north to east) and the Wells Tazhong 8-1 and Tazhong 5 fault zone (thrusting towards the south to east).