Phase Relationships in the System CaO-MgO-Al2O3-SiO2 in Plagioclase Lherzolite Field

Document Type



Master of Science (MS)



First Advisor's Name

Gautam Sen

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Rosemary Hickey-Vargas

Third Advisor's Name

Grenville Draper

Date of Defense



Unreversed phase equilibrium studies were carried out in a model mantle composition CaO-MgO-Al2O3-SiO2 (CMAS) system at 5-9 kb and 12 7 0-13 3 CPC. The experiments provide a set of data which narrowly constraints the position of the solidus in the system CMAS in the plagioclase lherzolite field. All runs were conducted in a 2.54 cm core-diameter piston-cylinder apparatus with salt-cell pressure medium. The equilibrium compositions of the mineral phases and glass were analyzed with an electron microprobe. The A12O3 contents in orthopyroxene and clinopyroxene coexisting with olivine and plagioclase increase with pressure. The deduced alumina isopleths in orthopyroxene and clinopyroxene have higher slope in P-T space than those of theoretical calculations. An empirical pyroxene geobarometer has been developed and applied to the plagioclase lherzolite xenoliths in Hawaiian basalt.



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