HR: 11:50h
AN: T22C-07    [Abstracts]
TI: Deep Orogen-parallel Electrically Conductive Troughs And The Relationship To Surface Deformation In Eastern Tibet And Indochina
AU: * Meju, M A
EM: m.meju@lancaster.ac.uk
AF: Lancaster University, Department of Environmental Science, Lancaster, LA1 4YQ, United Kingdom
AU: Bai, D
AF: Chinese Academy of Sciences, Institute of Geology and Geophysics, Beijing, 100029, China
AU: Ma, X
AF: Chinese Academy of Sciences, Institute of Geology and Geophysics, Beijing, 100029, China
AU: Jiang, C
AF: Seismological Bureau of Yunnan Province, Seismological Institute, Kunming, 650041, China
AU: Zhou, Z
AF: Seismological Bureau of Yunnan Province, Seismological Institute, Kunming, 650041, China
AU: Zhao, C
AF: Seismological Bureau of Yunnan Province, Seismological Institute, Kunming, 650041, China
AU: Wang, L
AF: China Seismological Administration, Institute of Geology, Beijing, 100029, China
AB: While it is accepted that the Cenozoic collision of India and Eurasia created the world's&plargest plateau in Tibet through a range of processes including crustal thickening, delamination and extrusion, the debate continues about which tectonic processes contribute to the overall mass balance of this continent- continent collision. Competing models explaining the post-collisional deformation in Himalaya and Tibet advocate eastward extrusion of rigid blocks between slip-surfaces (Tapponier et al. 2001) or ductile crustal flow decoupling the upper and lower parts of the lithosphere (Clark and Royden, 2000; Beaumont et al., 2001). Yet, the crustal and upper mantle structure in the southeastern Himalaya-Tibet regions remains poorly understood. It is pivotal for constraining the nature of lateral extrusion or ductile flow. We recently initiated a major regional study of the eastern Himalayan syntaxis (e.g. Sun et al. 2003). Here, we present the electrical conductivity images of the lithosphere across the eastern Tibetan Plateau and off- plateau in Indochina (lat. 25-32 deg. N, long. 97-105 deg. E) which suggest the presence of a coherent and geometrically similar orogen-parallel trough-like features of low electrical resistivity in the region. We compared our images to those published by other workers (Wei et al., 2001; Unsworth et al.2004) for the regions to the west and found the troughs to be a common regional feature. We find a continuous 10-30 km thick, electrically conductive crustal layer with two pronounced ca. 150-km-wide localised downwarps that are about 30-60 km deep and can be traced from the Tibetan plateau eastwards into Indochina. The lateral terminations of these low- resistivity troughs are marked on the surface by major E-W trending (Tibet) and N-S trending (Indochina) strike- slip faults. Their axes are parallel to the dominant surface structural trend suggesting coupling between upper and lower crust. Also, zones of Cenozoic volcanism appear to be spatially related to the crustal conductive layer suggesting a link between lower crustal conductivity heterogeneity and surface deformation in and off the Tibetan plateau. We suggest that the troughs are pre-existing fold structures or buried basins and that they probably influenced crustal melt distribution and deformation in the region. Our folding interpretation is shown to be consistent with inferences from gravity and topographical data (Jin et al.,1994; Braitenberg et al. 2000). References: Beaumont, C., R. A. Jamieson, M. H. Nguyen and B. Lee, Nature, 414, 738-742, 2001. Braitenberg, C., Zado, M., Fang, J., Wang, Y. & Hsu, H.T., J. Geodynamics 30, 489-505, 2000. Clark, M. K., L. H. Royden, Geology, 28, 703-706, 2000. Jin, Y., McNutt, M. & Zhu, Y. , Nature 371, 669-674, 1994. Sun, J., G. Jin, D. Bai, and L. Wang, Science in China, 46, 243-253, 2003. Unsworth M., Wei Wenbo, Jones A., et al., JGR, 109, B02403, doi:10.1029/2002JB002305, 2004. Tapponnier P., Xu Z., Roger F., Meyer B., Arnaud N., Wittlinger G., Yang J., Science, 294 (5547), 1671-1677, 2001. Wei W., Unsworth M., Jones A., et al., Science, 292 (5517), 716-719, 2001. Yin, A., T. M. Harrison, Annual Rev. Earth Planet. Sci., 28, 211-280, 2000.
DE: 8031 Rheology: crust and lithosphere (8159)
DE: 8102 Continental contractional orogenic belts and inversion tectonics
DE: 8108 Continental tectonics: compressional
DE: 8110 Continental tectonics: general (0905)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting