Collaborative Research: Is the Holocene Slip Rate along the Altyn Tagh Fault 10 mm/y, 30 mm/y, or Both? Infilling a 2-6 ka Data Gap Using 14C, OSL, and Stream Reconstructions

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The active, left-slip Altyn Tagh Fault extends for over 1200 km along the northwestern margin of the Tibetan Plateau, making it a first-order structure within the Indo-Asian collision. Measuring the Holocene slip rate along the Altyn Tagh Fault is essential for both advancing understanding of the mechanical behavior of major intracontinental fault systems and discriminating between conflicting rheological models of the Asian crust and lithosphere. Previous work has produced two contradictory slip rates for the central portion of the fault: GPS and paleoseismological studies give rates of about 10mm/y between 0.01 and 2-3 thousand years ago whereas geomorphic reconstructions yield rates of approximately 30 mm/yr between 6 and 113 thousand years ago. There is an important temporal gap in slip-rate data between 2 and 6 thousand years ago that may be explained by: (1) slip rate variations by a factor of three over a few thousand years; (2) constant and slow (about 10 mm/yr) slip rate in time; or (3) constant and fast (about 30mm/yr) slip rate in time. This three-year, integrated paleoseismic and slip-rate study along the central Altyn Tagh fault will distinguish between these three hypothesized slip histories for the 2 to 6 thousand year gap. Paleoseismological studies characterize the size, age, offset and magnitude of the most-recent surface-breaking ruptures. Slip rates are determined by reconstructing displaced fluvial terrace risers at six new sites. Displaced fluvial terraces are being measured and dated using radiocarbon, optically stimulated luminescence, and cosmongenic radionuclide methods. Establishing the Holocene slip history along the Altyn Tagh Fault is important for determining if Asia is best viewed as a collage of microplates or a thin viscous sheet.The Altyn Tagh Fault, the largest active strike-slip fault within the Indo-Asian collision, plays a central role in a long-standing debate over the deformational behavior of the Eurasian continent and, by implication, continents in general. At the heart of this debate lies a dispute over the rate at which the fault moved during the last 10,000 years. The results from this investigation will (1) resolve the disputed slip rate and allow distinction between the diffuse and localized continental deformation models; (2) provide observational constraints for models of intracontinental fault dynamics; and (3) improve understanding of the seismic risk to growing population centers near the Altyn Tagh Fault.