HR: 1330h
AN: T52A-0237    [PDF]
TI: Geophysical Models of Lithospheric Thinning Beneath the Alboran Sea Basin
AU: * Houseman, G A
EM: greg@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS8 2PF United Kingdom
AU: Hoogenboom, T
EM: trudi@earth.leeds.ac.uk
AF: School of Earth Sciences, University of Leeds, Leeds, LS8 2PF United Kingdom
AB: The Alboran Sea Basin in the western Mediterranean is a unique example of rapid and relatively extreme lithospheric thinning in the centre of a continental collision zone. Crust in the Alboran Sea Basin was thinned rapidly to 15-20 km at about 20 Ma while thrust faulting continued in the neighbouring Rif and Betic Cordillera. The region of lithospheric thinning is localised to less than 200 km in diameter, and major thrust systems lie almost on annular zones about the centre of the region. The probable cause of such localised lithospheric thinning is gravitational instability of a relatively dense and thick lithospheric root formed by continental collision. Previous numerical models of lithospheric instability have generally focussed on development of sheet-like structures in a 2D instability. Such models do not adequately represent the almost circular shape of the Alboran Sea Basin. Here we describe new models of the lithospheric gravitational instability in cylindrical axisymmetry. The axisymmetric model differs from the plane-strain model in that either central downwelling or central upwelling might be triggered and each can grow at the same rate, but the two possible developments have fundamentally different geological consequences. In particular, if the axisymmetric instability develops as a central upwelling, with peripheral downwelling, lithospheric thinning is concentrated in the central region and convergence develops in the crust above the peripheral downwelling. We examine the hypothesis that the Alboran Sea Basin may have developed by such a mechanism, comparing observations of surface topography and gravity anomalies with predictions of an axisymmetric model.
DE: 8102 Continental contractional orogenic belts
DE: 8109 Continental tectonics--extensional (0905)
DE: 8120 Dynamics of lithosphere and mantle--general
DE: 8159 Rheology--crust and lithosphere
DE: 8164 Stresses--crust and lithosphere
SC: Tectonophysics [T]
MN: 2003 Fall Meeting