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 85 0 degrees C, 200 MPa,f(O-2) approximate to NNO (nickel-nickel oxide oxygen buffer) as functions of total F and H2O content. Experiments employed the m etaluminous Mount Scott Granite of the Wichita igneous province, Oklahoma. Over a large range of added H2O (similar to 1-7 wt%), melts containing <1 w t% F precipitated titanite without fluorite, whereas melts containing >1 wt % F precipitated fluorite without titanite, In addition, at high F (greater than or equal to 1.2 wt%) plagioclase and hornblende reacted to form bioti te, Thus, an increase in F during crystallization may explain the observed higher modal abundance of plagioclase and hornblende in titanite-dominant s amples vs, higher modal biotite in fluorite-dominant samples within the Mou nt Scott Granite pluton. Coexistence of magmatic titanite and fluorite in t he Mount Scott Granite pluton implies F-m of similar to 1 wt% at the point in its crystallization history where these minerals coprecipitated. We sugg est that the presence of primary fluorite within high-temperature, shallowl y emplaced, moderate f(O-2), subaluminous felsic rocks indicates high magma tic fluorine, whereas titanite without fluorite in such rocks indicates low initial fluorine.