HR: 08:50h
AN: T31E-04    [Abstracts]
TI: Processes of Active Intraplate Deformation in the Mongolian Altai and Gobi Altai
AU: * Cunningham, D
EM: wdc2@le.ac.uk
AF: University of Leicester, Department of Geology, Leicester, LE17RH United Kingdom
AB: The Mongolian Altai and Gobi Altai regions are natural laboratories for studying active processes of intracontinental, intraplate transpressional mountain building. This type of orogen has unique structural, geomorphological and topographic characteristics that are generally underappreciated by geologists and geophysicists. Both ranges are dominated by 25 $\pm$5 km-spaced regional strike-slip faults which are linked to oblique-slip thrust and dip-slip thrust faults. These discrete belts of deformation and uplift are separated by non-extending sedimentary basins or geomorphologically mature landscapes. Individual ranges can be characterised as terminal restraining bends, double restraining bends, partial restraining bends, thrust ridges linked to strike-slip faults, triangular block uplifts between conjugate strike-slip faults, and individual thrust ridges. Neither orogen contains a regional thrust wedge, nor bounding foredeep, and structural vergence is inconsistent. Basins between ranges can be classified as ramp basins, confined asymmetric thrust-bound basins, open-sided thrust basins, strike-slip basins, and tectonically inactive remnant lows. Although parts of the Altai and Gobi Altai were previously a Mesozoic rift province, very few examples of fault reactivation and rift inversion have been identified in either region. The geometrical relationship between basement structural grain, rigid Precambrian block boundaries, and SHmax dictates Late Cenozoic fault kinematics and overall mechanisms of uplift. Ongoing transpressional deformation is incompletely slip partitioned as indicated by historical oblique-slip earthquake focal mechanism solutions and oblique-slip fault displacements as revealed by outcrop slickenside data. The geometry of active faulting is best described as regional transpressional duplexing, intermediate between strike-slip and thrust duplexing. Late Cenozoic upper crustal transpressional deformation may be balanced in the lower crust by crustal thickening due to lower crustal inflation, and possibly lower crustal outflow towards the Russian Altai-Sayan region where late Cenozoic plateau uplift is recorded, but unexplained.
DE: 8110 Continental tectonics--general (0905)
DE: 7209 Earthquake dynamics and mechanics
DE: 7218 Lithosphere and upper mantle
DE: 1020 Composition of the crust
DE: 1208 Crustal movements--intraplate (8110)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting