HR: 11:35h
AN: T22E-06    [Abstracts]
TI: Seismic Reflection Images of Deep Lithospheric Faults and Thin Crust at the Actively Deforming Indo-Australian Plate Boundary in the Indian Ocean
AU: * Singh, S C
EM: singh@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Carton, H
EM: carton@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Chauhan, A
EM: chauhan@igp.jusseiu.f
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Dyment, J
EM: jdy@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Cannat, M
EM: cannat@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Hananto, N
EM: hananto@ipgp.jusieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Hartoyo, D
EM: djoko@webmail.bppt.go.id
AF: BPPT, Jl MH Thamarin 8, Jakarta, 10340, Indonesia
AU: Tapponnier, P
EM: tappon@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AU: Davaille, A
EM: davaille@ipgp.jussieu.fr
AF: Institut de Physique du Globe de Paris, 4 Place Jussie, Paris cedex 05, 75252, France
AB: Recently, we acquired deep seismic reflection data using a state-of-the-art technology of Schlumberger having a powerful source (10,000 cubic inch) and a 12 km long streamer along a 250 km long trench parallel line offshore Sumatra in the Indian Ocean deformation zone that provides seismic reflection image down to 40 km depth over the old oceanic lithosphere formed at Wharton spreading centre about 55-57 Ma ago. We observe deep penetrating faults that go down to 37 km depth (~24 km in the oceanic mantle), providing the first direct evidence for full lithospheric-scale deformation in an intra-plate oceanic domain. These faults dip NE and have dips between 25 and 40 degrees. The majority of faults are present in the mantle and are spaced at about 5 km, and do not seem cut through the Moho. We have also imaged active strike-slip fault zones that seem to be associated with the re-activation of ancient fracture zones, which is consistent with previous seismological and seafloor observations. The geometries of the deep penetrating faults neither seem to correspond to faulting associated with the plate bending at the subduction front nor with the re-activation of fracture zone that initiated about 7.5 Ma ago, and therefore, we suggest that these deep mantle faults were formed due to compressive stress at the beginning of the hard collision between India and Eurasia, soon after the cessation of seafloor spreading in the Wharton basin. We also find that the crust generated at the fast Wharton spreading centre 55-57 Ma ago is only 3.5-4.5 km thick, the thinnest crust ever observed in a fast spreading environment. We suggest that this extremely thin crust is due to 40-50°C lower than normal mantle temperature in this part of the Indian Ocean during its formation.
DE: 3000 MARINE GEOLOGY AND GEOPHYSICS
DE: 3035 Midocean ridge processes
DE: 3039 Oceanic transform and fracture zone processes
DE: 8010 Fractures and faults
DE: 8100 TECTONOPHYSICS
SC: Tectonophysics [T]
MN: 2007 Fall Meeting