HR: 11:20h
AN: T52B-05    [Abstracts]
TI: On the Relationship Between Crustal Thinning, Faulting and Asymmetry Development During Rifting.
AU: * Perez-Gussinye, M
EM: mperez@ija.csic.es
AF: Institute of Earth Sciences `Jaume Almera' (CSIC), Lluis Sol‚ i Sabaris, s/n, Barcelona, 08028 Spain
AU: R. Ranero, C
EM: cranero@icm.csic.es
AF: Institute of Marine Sciences (CSIC)-ICREA, Paseo Maritimo de la Barceloneta 37-49, Barcelona, 08003 Spain
AB: Seismic data show that conjugate non-volcanic rifted margins typically display an asymmetry in the pattern of crustal thinning and faulting. While one margin is characterised by progressive crustal thinning and is heavily faulted, the conjugate side displays far abrupter crustal thinning and scarce large faults. Some examples include the West Iberia-Newfoundland, the South Labrador Sea and the Armorican-Flemish Cap conjugate margins. Early models for the formation of this asymmetry, commonly known as `detachment' models, invoked simple shear extension along lithospheric- or crustal-scale detachment zones. However, detachment faults have only been observed to occur at the edge of the thinned continental crust, where the crust is < 10 km thick, suggesting that they formed late in the rifting history and can not account for the large-scale asymmetry. Additionally, the fact that, on both margins of the conjugate system, the extension estimated from the geometry of faults blocks appear to be less than that measured from crustal thickness has been interpreted to imply lower crust flow away from the basin centre. This remains an enigmatic question, as large bodies of lower crustal material that should have resulted from this flow have not yet been detected. To understand how the crust thins as faulting progresses we have re-processed and pre-stacked depth migrated seismic lines from the West Iberia-Newfoundland conjugate system. The seismic images in depth allow to estimate with accuracy the extension attained on major faults. We show that only on the little faulted margin, crustal extension exceeds that attained by faulting, whereas on the heavily faulted margin extension measured on faults is approximately equivalent to crustal thinning. Based on our observations, we propose a conceptual model to explain how the crust thins progressively as deformation localizes and how this finally leads to the observed conjugate margin asymmetry.
DE: 1212 Earth's interior: composition and state (7207, 7208, 8105, 8124)
DE: 8109 Continental tectonics: extensional (0905)
DE: 8118 Dynamics and mechanics of faulting (8004)
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
DE: 8124 Earth's interior: composition and state (1212, 7207, 7208, 8105)
SC: Tectonophysics [T]
MN: Fall Meeting 2005