Rifting of the Galicia margin: crustal thinning and emplacement of mantle rocks on the seafloor

Abstract

Thinning of the continental crust beneath the western Galicia margin during rifting was associated with the emplacement of mantle-derived peridotite at the ocean-continent boundary. Tectonic denudation of upper mantle by normal shear of the lithosphere accounts for the processes of crustal thinning and the brittle deformation and ultimate emplacement of the serpentinized peridotite on the seafloor. On the other hand, the asthenosphere diapirism model is in agreement with the physical conditions inferred for the melting and ductile deformation of the peridotite. Therefore, we propose a composite model consisting of two stages: 1) asthenospheric upwelling of the peridotites beneath a poorly (if at all) thinned continental crust; and 2) crustal thinning and tectonic denudation of the cooled, poorly depleted peridotite by movement along a gently dipping normal detachment fault rooted in the upper mantle. This composite model accounts for all the data currently available from the Galicia margin. -from Authors