MULTIPHASE MESOZOIC EXHUMATION OF THE MONGOLIAN ALTAI, CENTRAL ASIAN OROGENIC BELT USING LOW-TEMPERATURE THERMOCHRONOLOGY

Regions such as the Mongolian Altai, Gobi-Tienshan, Siberia-Altai, and southwestern Tianshan of the Central Asian Orogenic Belt (CAOB) are characterized by substantial uplift and exhumation that occurred far from contemporary plate boundaries and continue to undergo active deformation. Recent studies in the NW Tianshan and Siberian-Altai Mountains suggest that inherited structures controlled deformation in the CAOB throughout Mesozoic and Cenozoic tectonic events.

This study uses low-temperature thermochronology, including apatite fission track and (U–Th)/He apatite fission track analysis to identify the exhumation episodes of the Mongolian Altai since the Mesozoic. We investigate both the timing of exhumation and test several hypotheses about the widespread post-Cretaceous burial of modern Altai uplifts.

Our strategy focused on taking samples from granitic plutons at different elevations including along vertical transects of Altai subranges. Data from these transects reveals the timing of the exhumation of basin bounding ridges and constrains their multi-phase exhumation and burial history. New apatite fission track data from the Mongolian Altai capture two periods of exhumation including in the early Jurassic (~195-165 Ma) and the early Cretaceous (130-110 Ma. These cooling ages match exhumation recorded across Central Asia including the northwestern Tianshan and Siberian Altai regions. Possible far-field tectonic mechanisms driving exhumation in the Mongolian Altai include the closure of the Mongol-Okhotsk Ocean the closure of the Paleo-Tethys Ocean (Jurassic), and the rotation of the Tarim block (Cretaceous).