Tectonic setting and structural evolution of the Late Cenozoic Gobi Altai orogen

Abstract

AbstractThe Gobi Altai is an intraplate, intracontinental transpressional orogen in southern Mongolia that formed in the Late Cenozoic as a distant response to the Indo-Eurasia collision. The modern range formed within crust constructed by successive terrane accretion and ocean suturing events and widespread granite plutonism throughout the Palaeozoic. Modern reactivation of the Gobi Altai crust and the kinematics of Quaternary faults are fundamentally controlled by Palaeozoic basement structural trends, the location of rigid Precambrian blocks, orientation of SHmax and possible thermal weakening of the lower crust as a result of an extensive history of Mesozoic–Cenozoic basaltic volcanism in the region, and the presence of thermally elevated asthenosphere under the Hangay Dome to the north. Modern mountain building processes in the Gobi Altai typically involve reactivation of NW–SE-striking basement structures in thrust mode and development of linking east–west left-lateral strike-slip faults that crosscut basement structures within an overall left-lateral transpressional regime. Restraining bends, other transpressional ridges and thrust basement blocks are the main range type, but are discontinuously distributed and separated by internally drained basins filling with modern alluvial deposits. Unlike a contractional thrust belt, there is no orogenic foreland or hinterland, and thrusts are both NE and SW directed with no evidence for a basal décollement. Normal faults related to widespread Cretaceous rifting in the region appear to be unfavourably oriented for Late Cenozoic reactivation despite widespread topographic inversion of Cretaceous basin sequences. Because the Gobi Altai is an actively developing youthful mountain range in an arid region with low erosion rates, it provides an excellent opportunity to study the way in which a continental interior reactivates as a result a distant continental collision. In addition, it offers important insights into how other more advanced intracontinental transpressional orogens may have developed during earlier stages of their evolution.