刘永江1, Franz Neubauer2, 葛肖虹1, Johann Genser2, 袁四化1, 李伟民1, 巩庆林3, 陈元忠3
1. 吉林大学地球科学学院 长春 130061; 2. Institute of Geology and Paleontology, Salzburg University Salzburg A-5020 Austria; 3. 东方地球物理公司敦煌分院 甘肃敦煌 736200
GEOCHRONOLOGY OF THE ALTUN FAULT ZONE AND RISING OF THE ALTUN MOUNTAINS
Liu Yongjiang1, Franz Neubauer2, Ge Xiaohong1, Johann Genser2, Yuan Sihua1, Li Weimin1, Gong Qinglin3, Chen Yuanzhong3
1. College of Earth Sciences, Jilin University, Changchun 130061; 2. Institute of Geology and Paleontology, Salzburg University, Salzburg A-5020, Austria; 3. Dunhuang Branch of Orient Geophysical Company, Dunhuang, Gansu 736200
The 40Ar-39Ar dating of the syntectonic growing micas, separated from the deformed augen gneiss and mylonitized granitic gneiss in the Mesozoic shear zone and strongly mylonitized greenschist in the Cenozoic shear zone from the transect across the Altun fault zone, yielded two age groups of 164.3~178.4 Ma and 26.3~36.4 Ma. Combining with the offset studies of the strike-slipping of Altun fault, it suggested that the ages of 164.3~178.4 Ma should represent the initial activity age (the latest Early Jurassic-Middle Jurassic) of the Altun strike-slip fault. After that, the strike-slipping activities along the fault occurred 85~100 Ma, 25~40 Ma and 8~10 Ma ago, respectively. The studies on the Cenozoic sediments showed the different contents of the sandstone framework components between the Xiaganchaigou (E3 g) and Shangganchaigou (N3 g )Formations in the western Qaidam Basin. With the sedimentary process, the quartz component decreased, the clastic component increased with more unstable minerals and worse sorting degree, which suggested that the Altun Mountains began to rise in Oligocene (sedimentary period of the Xiaganchaigou Formation). A strong uplifting happened in Late Miocene according to the evidence from the seismic section of the western Qaidam Basin and sedimentary velocity of the Qaidam and Tarim Basins. The last and strongest rising event occurred in the end of Early Pleistocene according to the unconformity between the Qigequan Formation (from the end of Pliocene to the beginning of Early Pleistocene) and the overlying sediments (Middle Pleistocene). Most of uplifting events were consistent with the isotopic ages recorded in the fault belt, indicating that the mountain uplifting should be related to the activities of strike slipping of the Altun fault zone.