HR: 1340h
AN: S13B-1065    [Abstracts]
TI: Strong Crustal Anisotropy Delineating the Himalayan Decollement
AU: * Schulte-Pelkum, V
EM: vera.schulte-pelkum@colorado.edu
AF: Dept. Geol. Sciences, University of Colorado at Boulder, 2200 Colorado Ave, UCB 399, Boulder, CO 80309 United States
AU: Sheehan, A
EM: afs@cires.colorado.edu
AF: Dept. Geol. Sciences, University of Colorado at Boulder, 2200 Colorado Ave, UCB 399, Boulder, CO 80309 United States
AU: Bilham, R
EM: roger.bilham@colorado.edu
AF: Dept. Geol. Sciences, University of Colorado at Boulder, 2200 Colorado Ave, UCB 399, Boulder, CO 80309 United States
AU: Wu, F
EM: francis@binghamton.edu
AF: SUNY Binghamton, PO Box 6000, Binghamton, NY 13902 United States
AB: Receiver functions recorded during the 2001-2003 HIMNT PASSCAL experiment in eastern Nepal and southern Tibet display strong and coherent variations in backazimuth, for both radial and transverse components. A strong, shallow signal observed from the Nepalese foothills to the High Himalaya can be modelled as a several kilometer thick, highly ($\sim$ 20%) anisotropic layer with arc-normal plunging symmetry (cf. $SKS$ splitting by Wu and Sheehan, this meeting). Its depth and gentle northward dip coincide with the decollement between India and the Himalaya inferred from structural geology and seismicity. The anisotropy may be caused by shear along the decollement; alternatively, it may already exist at the top of the Indian shield prior to entering the collision zone. Although data coverage decreases to the north, a layer with similar characteristics may be traced to depth in Tibet, dipping more steeply than the Moho under the High Himalaya and the southernmost edge of the Tibetan plateau. Farther north, there is evidence of a midcrustal conversion from a high-velocity layer in the lower Tibetan crust. This layer is substantiated by local tomography (Monsalve et al., this meeting). Our observations of a possible pinching down of the lower Indian crust, merging into a thinner, high-velocity layer, may be caused by eclogitization with its attendant change in volume.
DE: 7218 Lithosphere and upper mantle
DE: 7230 Seismicity and seismotectonics
DE: 8102 Continental contractional orogenic belts
DE: 8107 Continental neotectonics
DE: 7205 Continental crust (1242)
SC: Seismology [S]
MN: 2004 AGU Fall Meeting