DEFORMATION LOCALIZATION AND INTRAPLATE MOUNTAIN BUILDING IN THE ALTAIDS, CENTRAL ASIA

The huge deformation field associated with the Indo-Eurasia collision is a classic region to investigate active processes of crustal reactivation and strain localization in the continental crust. North of Tibet, intraplate deformation is localized in specific Late Cenozoic orogenic belts such as the North Tibetan foreland, Beishan, Tien Shan, and Gobi Altai. This talk will present a review of lithospheric controls on the localization, geometry and kinematics of these regions.

The Sanweishan and Nanjieshan of the North Tibetan Foreland represent the reactivated southern margin of the Archean, cratonic Tarim block. The rheological boundary between Paleozoic terranes in the Qilian Shan and the relatively stiff craton defines the northern boundary of Tibet (Altyn Tagh deforming belt) and explains the limited growth of contractional deformation into the adjoining craton. North of the Tarim-North China Craton, the reactivated Beishan-eastern Tien Shan and Gobi Altai orogens of the Gobi Corridor comprise the ‘soft core’ of Central Asia dominated by a mechanically weak assemblage of Cambrian-Permian terranes (“the Altaids”). The Gobi Corridor basement localizes Late Tertiary-Recent intraplate reactivation in response to compressional stresses derived from the Indo-Eurasia collision 2000+kms to the south due to: 1) diffuse Jurassic-Cretaceous Basin-and Range style crustal extension that thinned the crust and compartmentalized it into rift basins with variable thicknesses of sedimentary infill that likely generated variations in Moho temperatures; 2) thermal weakening of the crust due to widespread Paleozoic-Mesozoic granitization and Late Jurassic-Miocene basaltic volcanism; 3) pre-existing sutures, faults, metamorphic fabrics and sedimentary strike belts favorably oriented for reactivation; and 4) the presence of rigid Archean basement beneath the Hangay region of central Mongolia that serves as a ‘passive indentor’ focusing crustal reactivation around its southern and western margins. Phanerozoic terrane collages such as the Altaids, Alaska, western North American Cordillera, and European Hercynean belts are typically sites of repeated fault reactivation, deformation localization and intraplate earthquake hazards.