Electrical Structure Of The Lambda Ltyn Tagh Fault At The Changma Section And Its Tectonic Significance

At the eastern segment of the Altyn Tagh fault, the loss in strike-slip rate along the fault trace has been observed. As for the influence of the Altyn Tagh fault and the mechanism for variations in its strike-slip rates, additional evidences of the deep structure are needed. In this article, the Changma section of the Altyn Tagh fault is taken as a window for discussing the proposed problems. The magnetotelluric (MT) data along four profiles across the Altyn Tagh fault and the adjacent areas have been collected. The two-dimensional (2D) electrical resistivity model of each profile is obtained with a mature 2D inversion technique. In the electrical resistivity profiles, the mid-upper crust north to the Altyn Tagh fault is dominated by continuous high-resistivity bodies; while the electrical resistivity structure inside the Qilian Shan is complex with different anomalies in lateral direction. This general image is consistent with the regional tectonic setting. That is, the eastern margin of the Tarim Basin is in good integrity; while the Qilian Shan, as the leading edge of the growth of the northern Tibetan Plateau, is experiencing strong deformation. The electrical resistivity structure also reveals the variations of the faults in space. The cutting depth of the Altyn Tagh fault decreases significantly along its strike direction in the west of the Changma basin. The Altyn Tagh fault imaged as the resistivity contrast offsets southward about 15 km here, corresponding to a fault F18 and connecting with the Changma basin. The faults inside the north part of the Qilian Shan, including the Changma fault and the Hanxia-Dahuanggou fault, are generally in south and low-angle dipping direction. These faults cut through the top of high-resistivity anomalies. The Changma basin can act as a step-over bridging the faults here, so the strike-slip component of the Altyn Tagh fault is partly transferred to the Changma fault at the south side of the basin. Nevertheless, the Changma fault shows increasing strike-slip rate from west to east, the strike slip rate on the east section of this fault is even greater than the loss amount of the Altyn Tagh fault along its strike direction. Therefore, we consider that the major faults at the northern Tibetan Plateau are accommodating the compression strain by the remote effect of the India-Eurasia collision. The Altyn Tagh fault and the active faults inside the Qilian Shan are under transpression setting. Under this basic tectonic mode, the Altyn Tagh fault, F18, Changma basin, and the Changma fault constitute a local decomposition-conversion-accommodation system for the strike-slip rate; this system only affects local stress.