Abstract

To test the anatectic theory of migmatite formation, modal analyses and field studies were made of migmatites in Gilpin County, Colorado, and adjoining areas. The metasomes of a significant number of these migmatites were found not to fit the presently accepted definition of granite as a rock containing roughly equal proportions of quartz, orthoclase, and plagioclase. Field relationships show that many of the migmatites were derived from granite pegmatite dikes. Therefore, if anatexis is a factor in the genesis of the migmatites in this area this process must be relegated to a more remote stage of magma generation.

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