HR: 10:20h
AN: T32A-01 INVITED     [Abstracts]
TI: Oceanic detachment faults at the ultra-slow spreading Southwest Indian Ridge
AU: * Cannat, M
EM: cannat@ipgp.jussieu.fr
AF: CNRS, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AU: Sauter, D
EM: daniel.sauter@eost.u-strasbg.fr
AF: CNRS, Institut de Physique du Globe de Strasbourg, 5 rue Descartes, Strasbourg, 67084 France
AU: Escartin, J
EM: escartin@ipgp.jussieu.fr
AF: CNRS, Institut de Physique du Globe de Paris, 4 place Jussieu, Paris, 75252 France
AU: Mendel, V
EM: veronique.mendel@eost.u-strasbg.fr
AF: CNRS, Institut de Physique du Globe de Strasbourg, 5 rue Descartes, Strasbourg, 67084 France
AB: Our study focuses on the melt-poor, easternmost region of the Southwest Indian Ridge. We use the most extensive set of off-axis data available to date for an ultra-slow spreading ridge, extending up to about 28 myrs-old lithosphere, to discuss the characteristics and conditions of formation of corrugated surfaces. These surfaces extend 4 to 73 km along-axis (i.e. along-axis extension of inferred detachments), and 4 to 30 km in the spreading direction (i.e. cumulated offset along detachments). Some surfaces appear to have formed as part of a long-lasting episode of asymmetric large offset axial normal faulting. The most spectacular of such episodes affected a ridge length of 100 km, and lasted 6 myrs in the interval between magnetic anomalies 8 and 6, while spreading rates were faster (up to 29 mm/yr against 14 mm/yr between anomaly 6 and present). Individual corrugated surfaces of all ages face thicker gravity-derived crust in conjugate lithosphere, and correspond with positive residual topography, consistent with an origin in the footwall of large offset axial normal faults. Our observations further suggest that large-offset axial normal faults are actually more common than indicated by corrugated surfaces alone, and account for a sizeable proportion of lithospheric accretion at melt-poor ultra-slow ridges.
DE: 3035 Midocean ridge processes
DE: 3045 Seafloor morphology, geology, and geophysics
DE: 8004 Dynamics and mechanics of faulting (8118)
SC: Tectonophysics [T]
MN: Fall Meeting 2005