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Holocene Slip-Rate Along the Central Altyn Tagh Fault, NW China

R. D. Gold and E. Cowgill
Geology Department, University of California, Davis

The active, left-lateral Altyn Tagh Fault is the longest and most important fault system accommodating Indo-Asian convergence, north of the Himalayas. Previous Holocene slip-rate measurements along this fault have yielded contradictory results, with geodetic and paleoseismic studies reporting a rate of ~10 mm/yr, whereas longer-term geomorphic investigations report rates as high as 27 mm/yr. Three explanations can resolve these discrepant signals: (i) a temporal changes in slip-rate, (ii) spatial variability in slip-rate, or (iii) unconstrained methodological uncertainties in slip-rate calculations. To distinguish between these scenarios, we have made new slip-rate measurements at five sites featuring left-laterally faulted fluvial features along a 200 km reach of the central Altyn Tagh Fault, which spans the region of conflicting slip-rate sites. At our new study sites, we have documented faulted fluvial landform morphology with cm-resolution Tripod Light Distance and Ranging (T-LiDAR) topographic surveys integrated with neotectonic mapping made using a total station and remotely sensed satellite imagery. In addition, we have made ~180 radiocarbon and ~15 terrestrial cosmogenic radionuclide geochronologic measurements. From these datasets, we are developing 4-dimensional reconstructions that constrain the relationships between alluvial fan formation, lateral erosion, stream incision, and left-lateral faulting. Our results bracket the Altyn Tagh Fault sliprate to have ranged from 9-16 mm/yr since 9.5 ka. These results suggest that at the Holocene timescale, the fault does not display secularly or spatially varying slip-rate. Rather, our findings indicate that previous geomorphic slip-rate studies have not fully characterized the uncertainty in these types of measurements.

AAPG Search and Discover Article #90087 © 2008 AAPG/SEG Student Expo, Houston, Texas