Evolution of oceanic upper mantle structure

Love and Rayleigh wave phase velocities increase systematically with increasing age of oceanic lithosphere up to 150 Ma. The rates of increase differ between oceans and vary for different age intervals. Modeling of lithospheric age–phase velocity relations indicates that the high velocity seismic lid thickens and the velocities in the sub-lithospheric low velocity Ž . zone LVZ increase with age at different rates between oceans. The initial thickness of the lithosphere near mid-ocean ridges, as averaged by long-period surface waves, varies between 10 and 45 km, and 100 Ma lithosphere has thickness from 83 to 110 km, for models with isotropic shear velocities. Hotspots in oceanic areas appear to modify oceanic lithosphere evolution, producing deviations from average patterns with increasing age. q 1999 Elsevier Science B.V. All rights reserved.