Chloride bearing solutions were equilibrated with partially melted silicate rocks under two to eight kilobars fluid pressure, near the 700 degrees and 750 degrees C isotherms. Glasses, ranging in composition from granite to granodiorite and trondhjemite, were separated from the charges and were analyzed colorimetrically for their chloride content. The molal partition coefficient of chloride, K p (super Cl-) = m (sub Cl (super -) in melt) /m (sub Cl (super -) in aqueous phase) , decreases from 0.023 at two kilobars to 0.012 at six kilobars and then increases sharply to 0.077 at eight kilobars. This strong preference of Cl (super -) for the aqueous phase suggests that highly concentrated Cl (super -) brines can be produced during separation of H 2 O from a crystallizing magma.

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