HR: 14:15h
AN: T53D-03    [Abstracts]
TI: Composition, Temperature and Metamorphic Facies of the Lower Half of the Thickened Tibetan Crust From the North Kun Lun, Through Bayan Har Into the Qang Tang and Into the Himalaya-South Tibet: Insight on Their Geodynamical Evolution
AU: * Galve, A
EM: galve@ipgp.jussieu.fr
AF: Sismologie Experimentale, Institut de Physique du Globe, case 89, 4 place Jussieu, Paris cedex 05, 75252 France
AU: Jiang, M
EM: meij@public3.bta.net.cn
AF: Chinese Academy of Geological Sciences, Baiwanzhuang road, Beijing, 100037 China
AU: Hirn, A
EM: hirn@ipgp.jussieu.fr
AF: Sismologie Experimentale, Institut de Physique du Globe, case 89, 4 place Jussieu, Paris cedex 05, 75252 France
AU: Sapin, M
EM: sapin@ipgp.jussieu.fr
AF: Sismologie Experimentale, Institut de Physique du Globe, case 89, 4 place Jussieu, Paris cedex 05, 75252 France
AU: Laigle, M
EM: laigle@ipgp.jussieu.fr
AF: Sismologie Experimentale, Institut de Physique du Globe, case 89, 4 place Jussieu, Paris cedex 05, 75252 France
AU: de Voogd, B
EM: beatrice.devoogd@univ-pau.fr
AF: Dept. Sciences de la Terre, Universite de Pau, Pau, 64000 France
AU: Gallart, J
EM: jgallart@ija.csic.es
AF: Institute of Earth Sciences jaume Almera, calle Lluis Sole I Sabaris, Barcelona, 08028 Spain
AB: Wide angle reflection-refraction profiles of P and S-waves were obtained at the NE edge of the Tibetan Plateau of recent postcollisional active convergence tectonics, as well as into the earlier formed Himalaya-South Tibet. From the North Kun Lun through Bayan Har and into the Qang Tang block, the record-sections of six shots and their modelling evidence changes in crustal thickness, layers velocity and also image through fan profiles its internal architecture. Furthermore, recording of P-waves as well as unexpected S-waves gives insight of the lower crust physical state in the domain of block interaction in the northern edge of the Qang Tang and of the Bayan Har. Here, the quality factor Q is estimated in the lower half of the crust by accounting for the differential effect on amplitude-frequency, observed between waves of different penetrations. Attenuation values allow to exclude a significant proportion of partial melt and to estimate the homologous temperature, ratio in-situ to solidus temperatures. The latter depend on the physical conditions being dry, wet or dehydration melting, which are found different among the regions of the northern Bayan Har, northern Qang Tang and we will see also different from the Himalaya-South Tibet. Their in-situ temperatures differ also as estimated from their different Vp with similar felsic composition, highlighted by their low velocity ratio, Vp/Vs. The uncommon joint determination of several parameters: Vp, Vp/Vs, Qp and Qs reveals the composition, the mineralogy and hydration conditions of the lower half of the thickened crust of Tibet and backs up the thickening of the Tibetan crust by tectonic superposition, imbrication of originally normal thickness crusts.
DE: 9320 Asia
DE: 8159 Rheology--crust and lithosphere
DE: 5455 Origin and evolution
DE: 7205 Continental crust (1242)
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting