FINITE DURATION EXTENSION AND DECOMPRESSION MELTING

Decompression melting of the upwelling mantle during extension of continental lithosphere provides a viable mechanism for the magmatism observed in many rifted sedimentary basins and passive volcanic margins. A model has been developed in which, in addition to the adiabatic temperature decrease, syntectonic conductive cooling, melt transport and emplacement at crustal levels are accounted for. The heat equation including latent heat is solved numerically and the incremental melt fraction is traced to simulate dynamic melting. The emplaced magma is considered an integral part of the continental crust. We find that relative to an instantaneous rifting model with only adiabatic cooling, there is a more than 10% decrease in the melt thickness even when the duration of rifting is as short as 1 m.y. Whether extension takes place with constant horizontal velocity or strain rate has important implications for the amount of melt produced. Consequently, pressure-release melting does not only depend on the amount of stretching and duration of the rift episode, but also on how extension develops through time.