Finite Duration Rifting, Melting and Subsidence at Continental Margins

Abstract

When continental lithosphere is thinned during rift.in g. basall ic melt is generated by decompression of anhydrous mantle if the geotherm intersects the a nhydrous manl le solidus. The qu antity of melt generated depends on four principal factors: the degree of lilhospheric thinning; the potential temperature of the asthenospheric mantle; the thickness of the lithosphere prior to rifting; and t he duration of rifting. Subsidence at rifted continental margins can affected significantly by melt generation during rifting: mantle melting causes reduced subsidence because both the igneous rock added to t he crust and the residual mantle are less dens. then the original mantle. At ‘volcanic’ rifted margins subsidence is also affected by the relative uplift resulting from isostatic compensation of the underlying mantle whose density is reduced hy the thermal anomaly caused by the mantle plume. We present results from a uniform pure-shear lithospheric stretching model for melt generation and for subsidence at continental margins rifted at realistic finite rates. Predict ions from the model are compared with observations of melt generation and Subsidence from the ‘nonvolcanic’ Galicia Bank rifted margin and from the ‘volcanic’ Rockall Platieau rifted margin in the North Atlantic.