HR: 0800h
AN: T11C-1280    [Abstracts]
TI: Large Paleo Landslides Along the Western Part of the Gobi-Altay Fault System in Southwestern Mongolia
AU: * Mushkin, A
EM: mushkin@u.washington.edu
AF: University of Washington, Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195 United States
AU: Javkhlanbold, D
EM: javkhlan@yahoo.com
AF: Mongolian University of Science and Technology, Geoinformatics Center, Ulaanbaatar, 10000 Mongolia
AU: Bayasgalan, A
EM: bayas@must.edu.mn
AF: Mongolian University of Science and Technology, Geoinformatics Center, Ulaanbaatar, 10000 Mongolia
AU: Gillespie, A
EM: alan@rad.ess.washington.edu
AF: University of Washington, Department of Earth and Space Sciences, Box 351310, Seattle, WA 98195 United States
AB: A sequence of paleo landslides at the Namalzah Hills, $\sim$70 km south of the town of Altay in southwestern Mongolia (45.8\deg N, 96.5\deg E) is associated with tectonic activity along the western part of the Gobi-Altay Fault system (GAFS). Three mobilized blocks of 0.5, 2.5 and 110 km$^{2}$ suggest multiple events of sliding, and displaced alluvial fans across an adjacent fault trace at the front of the mountain range indicate left-lateral offset. The 110-km$^{2}$ block has been translated $\sim$4.5 km down-slope north from the mountain range, with prominent scarps defining both the eastern and western boundaries of the landslide. Neogene deposits unconformably overlain by Quaternary alluvial sediments up to 200 m thick in places comprise this block, which is structurally characterized by a set of internally drained basins trending east-west, and corresponding terminal lake beds. Well-developed desert pavements characterize its surface. The 0.5- and 2.5-km$^{2}$ blocks, which lie between the 110-km$^{2}$ block and the source area, appear to be younger and thus suggest sliding events that postdate the mobilization of the large block. Elevated alluvial fans found along the mountain front indicate significant antithetic uplift north of the mountain-front fault trace as well as $\sim$2 km of cumulative left-lateral offset. Surface-composition mapping of the largest block suggests 1.0-1.5 km of left-lateral offset between it and the mountain range, while westward translation of the smallest mobilized block indicates $\sim$0.6 km of post-sliding, left-lateral offset. OSL samples were collected from the bottom of a lake bed on the largest block and from the underlying alluvial sediments to provide age constraints for the initiation of these sliding events. The good preservation of carbon recovered from the bottom of the lake bed suggests that the lake is relatively young. Accordingly, slip-rates higher than the 1.2 mm/yr constrained by Ritz et al. (1995) along the eastern part of the GAFS, may be required to accommodate the 1.0-1.5 km of inferred offset between the largest block and the mountain range. While another landslide of similar magnitude has been described by Philip and Ritz (1999) $\sim$400 km to the east along the GAFS, the well-preserved sequence of mobilized blocks and closely related offset alluvial fans of the Namalzah Hills offers a good opportunity to improve our understanding of Quaternary displacement along this part of the GAFS, as well as study the complex relation between tectonic activity and landsliding in such intra-continental environments.
DE: 9320 Asia
DE: 8010 Fractures and faults
DE: 8040 Remote sensing
DE: 8107 Continental neotectonics
DE: 8110 Continental tectonics--general (0905)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting