Tectonic Setting and Structural Evolution of the Late Cenozoic Gobi Altai Orogen, Mongolia
Abstract
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 SHmax 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. The discovery of major Cretaceous normal fault systems in the Gobi Altai has important implications for workers investigating the region's neotectonic development, because the pre-existing rift basin architecture may have influenced the modern orogenic architecture and network of seismically active faults. Although the Gobi Altai has structural and basinal elements similar to continental transform systems undergoing transpressional deformation, such as the San Andreas system, it differs in several important aspects. The Gobi Altai is a reactivated mechanically weak belt between more rigid basement blocks in a continental interior. The Gobi Altai does not transfer plate motions, but terminally accommodates intraplate strain by oblique deformation. The Gobi Altai is a diffuse belt of deformation, but no singular strike-slip fault is dominant as is the case with the San Andreas Fault or Dead Sea Transform. 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. Preserved peneplain surfaces, fresh alluvial fans, and sharply defined fault scarps and active mountain fronts express a very strong tectonic signal, without the obscuring effects of a humid/high erosion rate climate signal. Finally, the Gobi Altai is a useful analog for how other more advanced intracontinental transpressional orogens such as the eastern Tien Shan and Altai developed during earlier stages of their evolution.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.T41E..04C
- Keywords:
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- 8002 STRUCTURAL GEOLOGY / Continental neotectonics;
- 8038 STRUCTURAL GEOLOGY / Regional crustal structure;
- 8110 TECTONOPHYSICS / Continental tectonics: general;
- 9320 GEOGRAPHIC LOCATION / Asia