ACTIVE CONTINENTAL INTERIOR DEFORMATION IN CENTRAL ASIA NORTH OF TIBET: LESSONS LEARNED THAT APPLY TO ALL CONTINENTS

Central Asia is often considered Earth’s greatest natural laboratory for investigating processes of continental interior reactivation. Actively deforming regions of the North Tibetan foreland, Hexi Corridor, Beishan, eastern Tien Shan, Gobi Altai, circum-Ordos Block, Altai-Sayan and Hangay-Hentei encompass an area larger than Alaska and Texas combined. Geodetic data suggest that intraplate reactivation in Central Asia is largely driven by the distant Indo-Eurasia collision, Asia’s retreating Pacific margin, and stored gravitational potential energy in Central Asia’s lithosphere. Thirty years of multi-disciplinary investigations in actively deforming regions north of Tibet lead to the following conclusions that are applicable to understanding the evolution of all continents in Earth history, and that will be the focus of this presentation: 1) Paleozoic terrane collages are mechanically weak and predestined for subsequent reactivation; 2) terrane-craton boundaries are strength discontinuities that localize reactivation; 3) strike-slip faults largely ignore pre-existing structures, whereas thrust faults reactivate, (and may invert) faults, fabrics and other pre-existing strike belts; 4) Tectonic loading is shared over wide regions and amongst numerous faults that unlike plate boundary scenarios, challenge individual fault recurrence models and earthquake forecasts; 5) The angular relationship between the modern SHmax and older “structural grain” is the dominant control on modern fault kinematics and the style of mountain building; 6) transpressional fault systems, transpressional duplexing, non-strain-partitioned oblique deformation belts and single or coalesced restraining bend massifs are common orogenic architectures; 7) lensoidal crustal domains that are similar to regional S-C fabrics define some deforming belts; 8) regional fold-and-thrust-belt tapered wedge systems rooted in low-angle decollements are absent, except in the Tien Shan; 9) conjugate strike-slip faults bound triangular wedge-shaped, tilted massifs in some regions – an interesting orogenic style; 10) ancient intracontinental, intraplate mountain ranges on other continents may go un-noticed by tectonicists, because their landscape expression may be geologically short-lived, with limited-to-no magmatic, metamorphic, and thermochronological signature.