TECTONIC SETTING AND STRUCTURAL EVOLUTION OF THE LATE CENOZOIC GOBI ALTAI OROGEN, MONGOLIA

The 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 Paleozoic. Modern reactivation of the Gobi Altai crust and the kinematics of Quaternary faults are fundamentally controlled by Paleozoic basement structural trends, the location of rigid Precambrian blocks, orientation of SH_max and possible thermal weakening of the lower crust due to 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-striking basement structures in thrust mode and development of linking E-W left-lateral strike-slip faults which crosscut basement structures within an overall left-lateral transpressional regime. Restraining bends, other transpressional ridges and thrusted 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 decollement. 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 a continental interior reactivates due to 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.