Phase relations of phlogopite and pyroxene with magnesite from 4 to 8 GPa: KCMAS–H2O and KCMAS–H2O–CO2
Author
Faculty Advisor
Date
2016
Keywords
experimental petrology, melting metasomatism, fluid, potassium, carbon cycling, phlogopite, richterite
Abstract (summary)
To constrain the melting phase relationships of phlogopite and magnesite in the presence of clino- and orthopyroxene, we performed experiments in the K2O–CaO–MgO–Al2O3–SiO2–H2O (KCMAS–H2O) and K2O–CaO–MgO–Al2O3–SiO2–H2O–CO2 (KCMAS–H2O–CO2) systems at pressures of 4–8 GPa and temperatures from 1100 to 1600 °C. We bracketed the carbonate-free solidus between 1250 and 1300 °C at 4 and 5 GPa, and between 1300 and 1350 °C at 6, 7 and 8 GPa. The carbonate-bearing solidus was bracketed between 1150 and 1200 °C at 4, 5 and 6 GPa, and between 1100 and 1150 °C at 7 and 8 GPa. Below the solidus in both systems at 4–6 GPa, phlogopite is in equilibrium with enstatite, diopside, garnet (plus magnesite in the carbonate-bearing system) and a fluid. At 7 GPa, phlogopite coexists with KK-richterite, enstatite, diopside, garnet (plus magnesite in the carbonate-bearing system) and a fluid. KK-richterite is the only stable K-bearing phase at 8 GPa and coexists with enstatite, diopside, garnet (plus magnesite in the carbonate-bearing system) and a fluid. In KCMAS–H2O, phlogopite is present to ~100 °C above the solidus. Olivine forms at the solidus and coexists with enstatite, diopside, garnet and melt. At depth in a subcontinental lithospheric mantle keel, phlogopite would be stable with orthopyroxene, clinopyroxene and magnesite to ~5 GPa along a 40 mW/m2 geotherm. A hydrous, potassic and CO2-bearing melt that intrudes the subcontinental mantle can react with olivine, enstatite and garnet, crystallizing phlogopite, magnesite and potentially liberating a hydrous fluid.
Publication Information
Enggist, A., & Luth, R. W. (2016). Contributions to Mineralogy and Petrology, 171, 88. doi:10.1007/s00410-016-1304-2
Notes
Item Type
Article
Language
English
Rights
All Rights Reserved