Abstract

Although the Altyn Tagh fault system has played an important role in the Indo-Asian collision, its geometry and tectonic evolution remain poorly known. Between 86° and 92°E, this system is at least 100 km wide and is bounded to the north and south by the North Altyn and Altyn Tagh faults, respectively. Mapping along the Jianglisai reach of the North Altyn fault indicates that Miocene(?) to Pliocene(?) motion was predominantly left to left-reverse slip, with transport vectors trending N45°–60°E. Map relationships suggest that total offset on the fault is >120 km. These results are inconsistent with previous models of the Altyn Tagh fault system in which oblique convergence along the northern margin of the Tibetan Plateau is partitioned into thrusting on the North Altyn fault and left slip on the Altyn Tagh fault. An alternative hypothesis is that the North Altyn fault is the northern boundary of a transpressional strike-slip duplex within which the structurally elevated Altyn Mountains were created. Our model suggests that transpressional deformation may be restricted to this strike-slip duplex and need not characterize the entire margin.

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