Experimental Study of Titanite-Fluorite Equilibria in the A-Type Mount Scott Granite: Implications for Assessing F Contents of Felsic Magma


Titanite and fluorite stability in melt were experimentally evaluated at 850 ⁰C, 200 MPa,f(O2) ≈ NNO (nickel-nickel oxide oxygen buffer) as functions of total F and H2O content. Experiments employed the metaluminous Mount Scott Granite of the Wichita igneous province, Oklahoma. Over a large range of added H2O (~1-7 wt%), melts containing 1 wt% F precipitated fluorite without titanite. In addition, at high F (≥1.2 wt%) plagioclase and hornblende reacted to form biotite. Thus, an increase in F during crystallization may explain the observed higher modal abundance of plagioclase and hornblende in titanite-dominant samples vs. higher modal biotite in fluorite-dominant samples within the Mount Scott Granite pluton. Coexistence of magmatic titanite and fluorite in the Mount Scott Granite pluton implies Fm of ~1 wt% at the point in its crystallization history where these minerals coprecipitated. We suggest that the presence of primary fluorite within high-temperature, shallowly emplaced, moderate f(O2), subaluminous felsic rocks indicates high magmatic fluorine, whereas titanite without fluorite in such rocks indicates low initial fluorine.


Geosciences and Geological and Petroleum Engineering

Keywords and Phrases

A Type Rock; Fluorine; Geochemistry; Granite

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Article - Journal

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© 1999 Geological Society of America (GSA), All rights reserved.

Publication Date

01 Oct 1999