My summer research in the experimental petrology lab focused on a specific question regarding partial melting of carbonated eclogite in the mantle.  Previous studies have shown that when subducted into the mantle, carbonate-bearing eclogite can produce carbonate melt (Yaxley (1999), Dasgupta et al. (2003)).  My project was executed in effort to gain more knowledge on this topic.  Specifically, I tested whether or not concentration and composition of the carbonate in the starting material (consisting of a carbonate composition and eclogite) had any effect on the temperature at which melt was first observed.  All experiments were performed at a constant pressure of 3.0 GPa in a piston cylinder high pressure apparatus in the Experimental Petrology Lab of the University of Minnesota.
Twelve experiments were performed.  Samples were prepared using eclogite (Salt Lake Eclogite, Hawaii) and one of three carbonate mixtures.  For the first set of experiments, a carbonate mixture (15% CO2) was used, containing sodium carbonate, siderite, magnesite, calcite, and potassium carbonate.  The second and third sets of experiments were prepared using 10 wt.% and 5 wt.% calcite as the source of carbonate.

After analyzing the experiments, it was determined that the concentration of carbonate did have an effect on the solidus temperature with respect to two characteristics of the starting material:
1. the concentration of alkali metals (such as sodium and potassium)
2. the Ca/Mg ratio of the bulk starting material

It was found that as the concentration of alkali metals in the starting material increased, the solidus temperature decreased.  In addition, it was observed that as the Ca/Mg ratio in the starting material was changed, the solidus temperature varied.
 

References:

Dasgupta, R., Withers, A.C., and Hirschmann, M.M. (2003).  Generation of Carbonatitic Melt through Partial Melting of Carbonated Eclogite Under Mantle Conditions.  Abstract Volume, 4th EUROCARB workshop, 15-16.

Yaxley, G.M. (1999).  Phase Relations of Carbonated Eclogite Under Upper Manlte PT conditions ? Implications for Carbonatite Petrogenesis.  7th International Kimberlite Conference, Gurney, J.J. et al. (eds), Rondebosch, South Africa, 933-939.
 
 
 
 

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