| Abstract: | We use the ratios between P and S wave velocities (VP/VS), derived from seismic refraction data, to infer the composition of the crust in the Grenville and the Appalachian Provinces of North America. The crust exhibits VP/VS increasing with depth from 1.64 to 1.84; there is a clear distinction between the Grenville Province (average VP/VS=1.81) and the Appalachian Province (average VP/VS=1.73) which persists at all depths. The boundary between these provinces is east dipping extending for 100 km east of the Champlain thrust. In the Appalachian Province the increase in VP/VS ratios with depth from 1.67 to 1.74 ?? 0.02 may reflect a normal decrease of silica content in the continental crust. In the Grenville Province beneath the Central Granulite Terrane, an anomalous VP/VS ratio of 1.82 ?? 0.02 is observed extending to a depth of 10 km; this correlates with the abundance of Ca-plagioclase in the Marcy Anorthosite. At greater depth (15-20 km), where seismic lamination and high electrical conductivity is observed, VP/VS is 1-84 ?? 0.02 and correlates with the Tahawus Complex, a layered mafic intrusion. Within the 25-km-thick lower crust of the Grenville Province the VP/VS is 1-84 ?? 0.02 and P-velocity is 7.0 ?? 0.1 km/s, which are typical for plagioclase-bearing rocks (gabbro-norite). The high VP/VS ratio in the Grenville Province has not been reported in crust of any other age. Since the Grenville Province contains 75% of the world‘s known anorthosites, high VP/VS ratio is related to high plagioclase. We suggest that the composition of the Grenville lower crust was significantly modified by the emplacement of the anorthosites in the mid-Proterozoic. Copyright 1997 by the American Geophysical Union. |
| Genre: | Article |
| ProdID: | 70019131 |
| Citation Author: | Musacchio, G.; Mooney, W. D.; Luetgert, J. H.; Christensen, N. I. |
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| Citation End Page: | 15241 |
| Citation Issue: | B7 |
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| Citation Language: | English |
| Citation Larger Work Title: | Journal of Geophysical Research B: Solid Earth |
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| Citation Number Of Pages: | 17 |
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| Citation Search Results Text: | Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from VP/VS ratios; 1997; Article; Journal; Journal of Geophysical Research B: Solid Earth; Musacchio, G.; Mooney, W. D.; Luetgert, J. H.; Christensen, N. I. |
| Citation Start Page: | 15225 |
| Citation Volume: | 102 |
| Citation Year: | 1997 |
| Type: | citation/reference |
| Text: | Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from VP/VS ratios; 1997; Article; Journal; Journal of Geophysical Research B: Solid Earth; Musacchio, G.; Mooney, W. D.; Luetgert, J. H.; Christensen, N. I. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| Date Other: | Wed, 1 Jan 1997 00:00 -0600 |
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