Influence of CO/sub 2/ on melting of model granulite facies assemblages: a model for the genesis of charnockites
Partial melting studies at crustal pressures in SiO/sub 2/-rich portions of the system KAlSiO/sub 4/-Mg/sub 2/SiO/sub 2/-H/sub 2/O-CO/sub 2/ can be used to model the anatectic origin of charnockites. The univariant reaction phlogopite + sanidine + quartz + vapor = enstatite + liquid produces a SiO/sub 2/-rich melt (granite analog) at 3 kbar; the vapor composition at the solidus is buffered to high H/sub 2/O-contents by the coexistence of phlogopite with its breakdown products. At higher pressures, 8 and 15 kbar, the fluid phase is buffered to higher CO/sub 2/-contents and the melt composition becomes enriched in K/sub 2/O and MgO (charnockite analog). Melting relations are controlled by the expansion of the quartz liquidus field relative to the enstatite and sanidine fields with increasing pressure. Partial melts generated at the base of the crust in the presence of a CO/sub 2/-rich fluid will be of an alkaline nature and will crystallize enstatite at lower pressures. CO/sub 2/-saturated melting of similar SiO/sub 2/-rich bulk compositions (phlogopite-absent) by the reaction enstatite + sanidine + quartz + CO/sub 2/ = liquid occurs at temperatures in excess of 1000/sup 0/C to about 15 kbar. Liquid compositions show analogous trends, however, with increasing pressure, to those observed in the 5-component system as a consequence of the expansion of the quartz liquidus surface relative to the enstatite surface.
- Research Organization:
- Lunar and Planetary Institute, Houston, TX
- OSTI ID:
- 5299358
- Journal Information:
- Am. Mineral.; (United States), Journal Name: Am. Mineral.; (United States) Vol. 66:11-12; ISSN AMMIA
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
580300* -- Mineralogy
Petrology
& Rock Mechanics-- (-1989)
ALKALINE EARTH METAL COMPOUNDS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
DATA
ENSTATITE
EXPERIMENTAL DATA
FLUIDS
GEOLOGY
GRANULITES
INFORMATION
MAGNESIUM COMPOUNDS
MAGNESIUM SILICATES
MELTING
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
NUMERICAL DATA
ORIGIN
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PETROLOGY
PHASE TRANSFORMATIONS
PRESSURE DEPENDENCE
PYROXENES
QUARTZ
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SILICON OXIDES