HR: 17:30h
AN: T34A-07 INVITED    [Abstracts]
TI: Modes of normal faulting and mantle exhumation at slow-spreading mid-ocean ridges. To what extent could they apply to ocean continent transitions ?
AU: * Cannat, M
EM: cannat@ipgp.jussieu.fr
AF: Institut de Physique du Globe, CNRS, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Sauter, D
EM: daniel.sauter@eost.u-strasbg.fr
AF: EOST, IPG, CNRS, 5 rue Descartes, Strasbourg, 67084, France, Metropolitan
AU: Lavier, L
EM: luc@ig.utexas.edu
AF: Jackson School of Geosciences, U. Texas, 4412 Spicewood Rd, Austin, TX 78759-8500, United States
AU: Escartin, J
EM: escartin@ipgp.jussieu.fr
AF: Institut de Physique du Globe, CNRS, 4 place Jussieu, Paris, 75252, France, Metropolitan
AU: Manatschal, G
EM: manatschal@illite.u-strabg.fr
AF: CGS, EOST, U. Strasbourg, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AU: Peron-Pivindic, G
EM: gwenn@eost.u-strabg.fr
AF: CGS, EOST, U. Strasbourg, 1 rue Blessig, Strasbourg, 67084, France, Metropolitan
AB: We use data from the Southwest Indian and Mid-Atlantic ridges to illustrate current concepts on the modes of exhumation of mantle-derived ultramafics in slow-spread oceans. We then compare these concepts with observations from slow-rifted, magma-poor, ocean continent transitions seismically imaged and drilled along the Iberia-Newfoundland margins. Preferred models for slow-spread oceans couple large offset normal faulting (detachment faults), with magmatic processes that prevent the formation of steady-state melt reservoirs at crustal levels. In extreme cases, volcanism is suppressed altogether. Proposed magmatic processes include reduced mantle melting, melt migration along-axis to focused volcanic centers, melt crystallization in discrete crustal intrusions, the freezing of melt into the lower lithospheric mantle, and inhibited melt transport in dykes through a thick axial lithosphere. Melt suppression due to conductive cooling of the mantle at very slow spreading-rates is probably not the dominant mechanism, except at ultra-slow or highly oblique ridges that overlie anomalously cold mantle. Detachment faults are inferred, based mostly on seismicity, to have dips > 40deg, and are found to be be active for < 3-4 myrs. Such relatively short lifetimes for individual faults do not necessarily prevent longer-lasting tectonic asymmetry between the two diverging plates. Dome-shaped, corrugated surfaces appear to form along the longer-lasting and larger offset faults, with large flexural rotation of the footwall, and under specific conditions of melt supply to the crust. Higher, or lower melt supply to the crust appears to result in shorter duration of slip on individual detachment faults (up to 1-2 myrs), and possibly in less pronounced footwall rotation. This suggests that faulting modes, and the distribution of weak zones in the axial lithosphere, are closely related with melt emplacement at crustal levels.
DE: 8105 Continental margins: divergent (1212, 8124)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8178 Tectonics and magmatism
DE: 8416 Mid-oceanic ridge processes (1032, 3614)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting