The problem is raised as to whether a granitic magma under high pressure conditions would form a water solution immiscible with the residual silicate solution as crystallization proceeds. The composition of the rest-magma, after 96 percent crystallization of a magma which contained 2 percent of water, is calculated. Experiments showed that the rest-magma would be separated into two liquid phases between 290 degrees and 550 degrees C. under a pressure equivalent to a depth of 10 kilometers. A two-component approximate phase diagram, based on data of R. W. Goranson and analyses of the immiscible liquids, is deduced. It is concluded that granitic magmas form two immiscible residual solutions during a stage in their crystallization.

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