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Mineral and rock compositions of mafic enclaves in the Morton Gneiss

By
BRUCE V. NIELSEN
BRUCE V. NIELSEN
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PAUL W. WEIBLEN
PAUL W. WEIBLEN
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Published:
January 01, 1980

Two major mineralogic types of mafic enclaves (amphibolite and pyroxene-amphibolite) have been characterized in the Morton quartzofeldspathic gneiss at Morton, Minnesota. Some amphibolite contains plagioclase megacrysts with An66 cores and An43 rims. One indication of compositional equilibration of the amphibolite with host gneiss is the presence of biotite-rich rims on many enclaves. Textural and compositional reaction relationships observed in the mafic enclaves may be interpreted as relict igneous features. Bulk compositional data from three representative enclaves at Morton suggest that the pyroxene amphibolite could be derived from amphibolite by crystal fractionation and that both enclave types could have crystallized from a tholeiitic magma.

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GSA Special Papers

Selected Studies of Archean Gneisses and Lower Proterozoic Rocks, Southern Canadian Shield

G. B. Morey
G. B. Morey
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Gilbert N. Hanson
Gilbert N. Hanson
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Geological Society of America
Volume
182
ISBN print:
9780813721828
Publication date:
January 01, 1980

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