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NARROW
GeoRef Subject
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all geography including DSDP/ODP Sites and Legs
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Canada
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Eastern Canada
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Ontario (2)
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Europe
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United States
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Alabama (1)
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Michigan
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Minnesota
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Wisconsin
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Primary terms
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North America
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orogeny (6)
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Paleozoic
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Cambrian
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Upper Cambrian
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Mount Simon Sandstone (1)
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Carboniferous
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Mississippian
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Upper Mississippian
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Hartselle Sandstone (1)
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Ordovician (1)
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plate tectonics (1)
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Precambrian
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Animikie Group (1)
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Archean
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Gunflint Iron Formation (1)
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upper Precambrian
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Proterozoic
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Algonkian
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Baraboo Quartzite (1)
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Keweenawan
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Copper Harbor Conglomerate (1)
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Mesoproterozoic
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Freda Sandstone (1)
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Negaunee Iron Formation (1)
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United States
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Watersmeet
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.
On the origin of Early Proterozoic gneiss domes and metamorphic nodes, northern Michigan
SHRIMP study of zircons from Early Archean rocks in the Minnesota River Valley: Implications for the tectonic history of the Superior Province
Sm-Nd model ages on a whole-rock sample of the gneiss at Watersmeet, Michigan, show that these rocks were added to the continental crust about 3,600 m.y. ago. These model ages are calculated by assuming that the rocks were derived from a mantle reservoir with the Sm/Nd ratio of CHUR, which corresponds approximately to the chondritic ratio. These data confirm the U-Th-Pb zircon results that indicated a minimum age of 3,410 m.y. and possibly an age as old as 3,800 m.y. This study further illustrates the utility of Sm-Nd model ages in deciphering the history of complex Precambrian terranes.