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Early and Middle Proterozoic History of the Great Lakes Area, North America

W. R. Van Schmus
Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences
Vol. 280, No. 1298, A Discussion on Global Tectonics in Proterozoic Times (Jan. 22, 1976), pp. 605-628
Published by: Royal Society
Stable URL: http://www.jstor.org/stable/74580
Page Count: 24
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Early and Middle Proterozoic History of the Great Lakes Area, North America
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Abstract

Two major supracrustal sequences, the Huronian Supergroup in Ontario and the Marquette Range Supergroup and Animikie Group of Michigan and Minnesota, overlie an Archean basement. These sequences are about 2200-2300 Ma and 1900-2000 Ma old respectively. The major Early Proterozoic tectonic event is the 'Penokean Orogeny', which occurred about 1850-1900 Ma ago and included deformation, high-grade regional metamorphism, and extrusive and intrusive igneous activity. This was followed by formation of rhyolitic, ignimbritic volcanic rocks and emplacement of associated granites about 1790 Ma ago. The entire region was subsequently subjected to low-grade regional metamorphism 1650-1700 Ma ago, followed by emplacement of anorogenic quartz-monzonite, in part rapakivi, plutons 1500 Ma ago. Late Proterozoic Grenville and Keweenawan events represent the youngest major Precambrian activity in the region. The rocks involved in the Penokean Orogeny lie along the southern margin of the Archean craton of the Superior Province and are interpreted as representing Early Proterozoic cratonic-margin orogenic activity. The distribution of rocks types and structures associated with the Penokean Orogeny and with similar orogenic belts along the margin of the Archean craton of North America suggest that these orogenic belts may have formed as a result of processes similar to modern plate tectonics, although the data are far from conclusive at present.

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