Fluorian garnets from the host rocks of the Skaergaard intrusion: implications for metamorphic fluid composition

C. E. Manning; D.K. Bird

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USGS · 70015926

Fluorian garnets from the host rocks of the Skaergaard intrusion: implications for metamorphic fluid composition

C. E. Manning·D.K. Bird

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Abstract

Zoned, silica-deficient, calcic garnets containing up to 5 mol% F substitution for O formed during contact metamorphism of basalts by the Skaergaard intrusion in East Greenland. Fluorian calcic garnets occur as a retrograde alteration of prograde wollastonite and clinopyroxene that fills vesicles and vugs in lavas 30-70 m from the intrusion. The F content of garnet is extremely sensitive to minor changes in fluid composition. The calculations show that a decrease in pH or an increase in log aF- of 0.3 at constant pressure and temperature will decrease the F concentration in garnet from 5 to 0 mol%. The results of this study show that fluorian hydrous grandites provide a mineralogical record of the activities of F species in coexisting metamorphic and hydrothermal fluids. -from Authors

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C. E. Manning, D.K. Bird. 1990. Fluorian garnets from the host rocks of the Skaergaard intrusion: implications for metamorphic fluid composition. https://pubs.usgs.gov/publication/70015926

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