Using Constraints from Experimental Petrology Studies to Model Mantle Melting Processes under Anhydrous and Hydrous Conditions

Abstract

The information obtained from mantle peridotite and mantle-analog melting studies provides fundamentally important constraints for the development of mantle melting models which integrate the thermal, mechanical and chemical interactions between melt and mantle. The goal of the models is to use the information preserved in the chemistry of basaltic magmas to infer melting processes. In the case of anhydrous melting beneath mid-ocean spreading centers, the general characteristics of melting process are understood. In this environment melting occurs during adiabatic ascent and mantle melting begins when the temperature exceeds that of the solidus. Magmatic output is determined by mantle temperature, melt production rate, the geometry of melt production and melt migration, mantle flow in response to melting-induced buoyancy and thermal structure effects and by mantle bulk composition. Chemical information from mantlederived melts can be used to deduce geometric and physical aspects of melting during adiabatic ascent. In the case of hydrous mantle melting that occurs above the subducted slab in convergent margin and island arc environments, the fundamental controls on melt generation are less firmly established and chemical compositional information preserved in magmas can provide insight into the depth range over which melt is generated, the thermal structure of the melting regime and the physical aspects of the melting processes.