ANHYDROUS PARTIAL MELTING OF MANTLE PERIDOTITE AT 2GPA
The research I conducted this summer in the Hirschmann lab was a continuation of last summer's project dealing with trapping and analyzing small percent partial melts of peridotite. The focus of this summer's work was to finish analyses of all the charges and determine the melt fraction as well as the character of the quenched liquid.
Low percent partial melt data is important for experimentally constraining the process of basalt formation. Pressures of 2GPa are most pertinent in the evolution of mid-ocean ridges basalts. This work is closely related to graduate student Fred Davis' work at 3GPa, more relevant to ocean-island basalt formation.
A total of 18 experiments with rhenium foil traps were run in the piston cylinder at 2GPa between 1320-1420°C. Three charges were able to be fully characterized and a mass balance was used to find the melt fraction. The lowest melt fraction determined was 19% at 1360°C. Some experiments at 1340°C possessed trapped melt within the rhenium fold but were still too small to analyze, and experiments at 1320°C were determined to be subsolidus.
This 2GPa data helps fill the substantial gap in knowledge concerning chemical character of liquids as well as the other phases at near solidus temperatures. Additional information aside from melt composition was gleaned from this project including aluminum concentration within pyroxene. Aluminum has been correlated to partitioning of water in pyroxenes which in turn affects melting temperature and position of the solidus. Affects of hydrous melting were better explored by Kayla Iacovino in a related project and were compared to the melting temperatures of these dry experiments.
It is still hopeful that these traps can be an effective tool for analysis. Visually, the charge seems to have less melt than the mass balance calculates. A recalculation with additional glass analyses may prove to give a better result with a smaller percent melt.