Upper mantle deformation and seismic anisotropy in continental rifts

We investigate the seismic anisotropy signature of the continental rifting process. Several sources of anisotropy are considered: the lithospheric deformation, the asthenospheric flow and the occurrence of oriented melt-pockets in the asthenospheric mantle. Our results show that contrasted anisotropy patterns should be associated with the various conceptual models of rifting. Thus seismic anisotropy measurements may allow one to discriminate between these models. Anisotropy measurements in the Rio Grande, East-African and Rhine rifts suggest that these rifts formed by a transtensional deformation of the lithospheric mantle rather than by homogeneous extension of the lithosphere. Alignment of melt-lenses in the asthenospheric wedge may also account for a significant part of the seismic anisotropy recorded in the internal domains of these rifts. (C) 2000 Elsevier Science Ltd. All rights reserved.