Melt Generation and Extraction in Mantle Diapirs

Abstract

The oceanic lithosphere, its physical, penological and geochemical nature, are largely a function of the magmatic processes which take place at oceanic spreading centers. An understanding of the processes of mantle melting and melt extraction is therefore central to models for the development of oceanic lithosphere. Such models may need to be adapted and modified because of the specific features of the accretion site: mid-oceanic ridge, island arc or back-arc environments, but the basic principles still hold. The processes of melt extraction and magma segregation need to be considered from both physical and geochemical points of view, taking into account the observations from the ocean basins, and from ophiolite complexes and the experimental results on peridotite and basalt compositions. The data on ophiolite complexes have an important role to play here since information on the deep structure and deep processes in the ocean basins is largely an extrapolation from surface observations. In ophiolite complexes there is the potential to extend these observations down to as much as 15 km into the underlying peridotitic mantle. Observations in such peridotite massifs can be complemented by those made in peridotite xenoliths from alkali basalts, of which some derive from the deep horizons where basalts are generated.