Evidences from ESR Dating for Structural Deformation of Altyn Tagh Fault System Since Middle Miocene

The study on the initial activity time and mechanism of Altyn Tagh fault system since Cenozoic is one of hot topics in the northern Tibet Plateau,but is still lack of a reliable chronological constraint.Based on field investigation,the ages of associated quartz vein and gypsum from Altyn Tagh fault system were measured by electron spin resonance(ESR)dating,and the age was taken as the constraint of the latest fault activity;the structural deformation of Altyn Tagh fault system since Middle Miocene was discussed.The results show that Cenozoiclarge-scale structural deformation of Altyn Tagh fault system starts in Middle Miocene((12.5±1.3)-(15.1±1.5)Ma),followed by multistage activities;time limit of large-scale strike-slip activity for Altyn Tagh main fault at least starts in(15.1±1.5)Ma,but time limit of compression thrust activity for the northern Altyn Tagh fault at least starts in(14.1±1.4)Ma;there is a time difference for the activity between Altyn Tagh main fault and the northern Altyn Tagh fault,suggesting that Altyn Tagh fault system extends progressively from the center to both sides;the deep ductile shear leads to strike-slip movement of Altyn Tagh main fault and rapid uplift of neighbouring mountain,and then the deformation propagation cause the tectonic response of thrust activity of the northern Altyn Tagh fault.