| Abstract: | This ophiolite was obducted in the early Ordovician during the closing of the proto-Atlantic. The tectonized peridotite of the lower unit of the ophiolite is intruded by felsic dykes and pods, including isolated lenses of massive rodingite, small bodies of strongly deformed diorite, and younger, less deformed monzonite. These intrusions are found only near the base of the ophiolite, and are considered to have been emplaced before the ophiolite reached its present position. The young group of intrusions consists of biotite-muscovite quartz monzonite and leuco-quartz monzonite. Analysed samples have high K2O, high (K2O X 100)/Na2O + K2O) ratios, and high initial Sr ratios, indicating that the magma source was continental and that these felsic rocks formed by partial melting of continental sediments. Whole-rock and mineral isochron ages suggest that the felsic intrusions are approx 456 + or - 4 m.y. old and that they were metamorphosed approx 418 + or - 7 m.y. ago. The detachment of the ophiolite occurred approx 491 + or - 3 m.y. ago. The felsic dykes were intruded approx 35 m.y. later, during the Taconic orogeny. The lengthy time between detachment and final nappe emplacement recorded by the felsic dykes may be a requirement for formation of abundant asbestiform chrysotile. Whole-rock analyses (16) and Rb, Sr and 87Sr/86Sr data from the Colline de Granite, King Mts., Vimy Ridge and Black Lake samples are presented.-P.Br. |
| Genre: | Article |
| ProdID: | 70013137 |
| Citation Author: | Clague, D. A.; Frankel, C. S.; Eaby, J. S. |
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| Citation End Page: | 1261 |
| Citation Issue: | 9 |
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| Citation Language: | English |
| Citation Larger Work Title: | Canadian Journal of Earth Sciences |
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| Citation Number Of Pages: | 5 |
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| Citation Search Results Text: | The age and origin of felsic intrusions of the Thetford Mines ophiolite, Quebec.; 1985; Article; Journal; Canadian Journal of Earth Sciences; Clague, D. A.; Frankel, C. S.; Eaby, J. S. |
| Citation Start Page: | 1257 |
| Citation Volume: | 22 |
| Citation Year: | 1985 |
| Type: | citation/reference |
| Text: | The age and origin of felsic intrusions of the Thetford Mines ophiolite, Quebec.; 1985; Article; Journal; Canadian Journal of Earth Sciences; Clague, D. A.; Frankel, C. S.; Eaby, J. S. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Tue, 1 Jan 1985 00:00 -0600 |
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