Anisotropy of magnetic susceptibility of Eolian sediments in Altun Shan: implications for Altyn Tagh Fault tectonics since Pleistocene

Abstract:

Ancient windblown (eolian) dust, such as in Chinese Loess Plateau (CLP), are treasured for understanding the evolution of aridity and influence by Plateau（mountain）uplift on climate change. Anisotropy of magnetic susceptibility (AMS) is an effective tool in tracking atmospheric direction under weak to moderate speed currents to reconstruct the paleomonsoon model was studied in recent years. Whilst it is sometimes directly or indirectly associated with the effects of tectonic process and developed as a results of burial diagenesis process for these eolian sediments. Here we firstly investigated AMS in a Red clay sequence (eolian deposits during Miocene to Pliocene) accumulated in the margin of Altun Mountains, which has the similar mineral content as that in CLP. The average north-west orientations of minimum magnetic susceptibility (K_min) axes is tilting towards the active Althy Tagh Fault direction and the average direction of intermediate magnetic susceptibility (K_int) axes is close to be vertical and compacted by the gravity as a second force. The average maximum magnetic susceptibility (K_max) is perpendicular to either tectonic or gravity directions. Considering there is no obvious metamorphic effects and plastic deformation of particles, we attribute these two stresses determined the transition of petrofabrics from the deposition to tectonics, by the intensified Pleistocene activity of Altyn Tagh Fault.