Date of Award

1985

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Geology

First Advisor

D. Perkins, III

Abstract

Metasediments of the Precambrian English River subprovince, a subdivision of the Superior province, are conspicuously migmatized by 'bands of light-colored, igneous-appearing material. The metasediments them.selves consist of alternating layers of pelite and wacke lithologies, which represent original mudstones and graywackes respectively. Their deposition is thought to represent subaqueous turbidity flows.

For the metasediments of the study area, a 250 square kilometer portion of the English River subprovince, metamorphic grade increases southward from the English River subprovince's northern border. Two isograds have been mapped: the disappearance of muscovite and the disappearance of stable sillimanite. Geothermometry studies are consistent with the trend in metamorphism and temperature values indicate an essentially east-west trending thermal anticline near the center of the subprovince's northern metasedimentary domain. Granulites, defined by the presence of orthopyroxene, occur in the highgrade metasediments near the center of the thermal anticline. Water activities appear to decrease with increased metamorphic grade.

Melting reactions in both pelites and wackes are consistent with phases in small, leucocratic, isolated patches of what is thought to be anatectite in the metasediments. These llallle melting reactions cannot always explain the conspicuous layered leucosome layers which must have been introduced into the metasediments by injection. Structural and chemical observations are also consistent with an injection mechanism for the formation of the area's layered migmatites. The source of the injected material is most likely from extensive fusion of the metasedimentary pile at greater depths.

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