Late Pleistocene slip rate of the Hoh Serh-Tsagaan Salaa fault system, Mongolian Altai and intracontinental deformation in central Asia

摘要

The Mongolian Altai is an intracontinental oblique contractional orogen related to the far-field effects of the Indo-Asian collision. Global Positioning System (GPS) data suggest that ~10-15 per cent of total Indo-Asia convergence is accommodated across this orogen. The Höh Serh-Tsagaan Salaa fault system is one of several NNW-SSE-trending oblique contractional faults acting to partition strain and accommodate shortening and dextral shear in the Mongolian Altai. This fault zone displaces late Pleistocene alluvium along the southwest piedmont of the Höh Serh range in western Mongolia. Along the central third of the fault zone, strain is partitioned onto two separate strands, one that accommodates nearly pure dextral shear and one that accommodates thrust motion. We determined late Pleistocene rates of deformation along each of the Höh Serh-Tsagaan Salaa fault strands based on differential GPS surveys and cosmogenic nuclide 10Be geochronology. Combining the measured offsets and 10Be dates yields a minimum right-lateral slip rate of 0.9 +0.2/-0.1 mm a-1; the minimum shortening rate is 0.3 ± 0.1 mm a-1, with uplift of at least 0.1 ± 0.1 mm a-1. Resolving the shortening and dextral components of deformation yields a slip vector of 0.8 +0.2/-0.1 mm a-1 toward 336°. This long-term deformation vector is consistent with the short-term strain field determined by GPS in the region and indicates that ~20 per cent of Indo-Asian deformation in the Mongolian Altai (~2 per cent of the total Indo-Asia strain accumulation) occurs along the Höh Serh-Tsagaan Salaa fault zone. Although rate data for other active faults in the Mongolian Altai are sparse, our results suggest that strain may be accommodated almost exclusively on discrete structures in this intraplate tectonic setting. © 2010 The Authors Geophysical Journal International © 2010 RAS.