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Tonalitic gneiss of early Archean age from northern Michigan

By
Z. E. PETERMAN
Z. E. PETERMAN
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R. E. ZARTMAN
R. E. ZARTMAN
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P. K. SIMS
P. K. SIMS
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Published:
January 01, 1980

The Marenisco-Watersmeet area in the western part of the northern peninsula of Michigan contains a greenstone and granite terrane (Puritan Quartz Monzonite) of late Archean age on the north and a gneiss terrane (gneiss at Watersmeet) on the south. A granite and gneiss belt (collectively called the granite near Thayer) crops out between these contrasting terranes. Lower Proterozoic metasedimentary and metavolcanic rocks of the Marquette Range Supergroup are extensive.

Radiometric dating of the tonalitic phase of the gneiss at Watersmeet establishes an early Archean age and a complex subsequent history. U-Th-Pb systematics provide a firm minimum age of 3,410 m.y. with the possibility of a much greater age—3,500 to 3,800 m.y. Cataclasis and recrystallization during the early Proterozoic Penokean orogeny are recorded on a regional scale by whole-rock and mineral Rb-Sr ages of 1,750 m.y. Intense cataclasis of granodioritic gneiss in the Watersmeet dome locally produced metamorphic zircon with concordant ages of 1,755 m.y.

Zircons from a tonalitic phase of the granite near Thayer are dated at 2,750 m.y. Zircons from leucogranite dikes, which are abundant in the tonalitic phase of the gneiss at Watersmeet, are slightly younger at 2,600 m.y. These intrusive rocks are approximately contemporaneous with the development of the greenstone-granite terrane of late Archean age.

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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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