Experimental Investigations on the Role of H20 in Magmatic Processes

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

The proposed experiments will provide constraints on the influence of water on mantle melting and on crustal differentiation processes. The studies will provide information on the temperature, volatile content and pressure of melting and fractional crystallization. The cycling of water through the Earth's interior is of fundamental importance for understanding the chemical evolution of the Earth over geologic time. Processes of solid - liquid differentiation (crust formation, mantle differentiation and core segregation), of the origin of the oceans and of life on Earth are tied to the cycling of H2O through our planet's deep interior. Three projects are proposed. 1) A systematic investigation of the influence of H2O on the liquidus of natural basaltic melts. These experiments will provide quantitative information that can be used to model the H2O-undersaturated melting of silicates in the presence of variable amounts of H2O, and should help resolve the considerable uncertainty on the influence of small amounts of H2O on melting. 2) Investigation of the role of H2O, pressure and mantle composition on peridotite melting. These experiments will provide quantitative estimates of the role played by H2O and bulk composition (primarily the alkali elements Na2O and K2O) on the generation of magmas in subduction zone and sub continental mantle environments. 3) Experimental studies of the role of H2O and pressure on fractional crystallization of basaltic melts in the crust. In arc magmatic systems the compositional characteristics of differentiated arc magmas and their mineral assemblages can provide evidence of the pre-eruptive H2O content, temperature and depth history of differentiation. For all of the preceding studies we will develop thermodynamically based analytic models that allow prediction of conditions of melting/crystallization and compositions of melts generated when H2O is involved. These studies will place quantitative constraints on the influence of H2O on the chemical evolution of the Earth's crust and mantle. This information on H2O will be of broad interest in the geodynamics and mineral physics community and ultimately has relevance for the origin of the Earth's oceans and life on Earth. This project will train graduate and undergraduate students in research methods of experimental petrology/geochemistry. The experimental data that results from this study will be shared with the community and models for predicting temperature, H2O content and pressure of melting/crystallization will be developed and distributed.