In:
Journal of Geophysical Research: Solid Earth, American Geophysical Union (AGU), Vol. 102, No. B7 ( 1997-07-10), p. 15225-15241
Abstract:
We use the ratios between P and S wave velocities (V P /V S ), 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 V P /V S increasing with depth from 1.64 to 1.84; there is a clear distinction between the Grenville Province (average V P /V S =1.81) and the Appalachian Province (average V P /V S =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 V P /V S 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 V P /V S 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, V P /V S 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 V P /V S 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 V P /V S 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 V P /V S 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.
Type of Medium:
Online Resource
ISSN:
0148-0227
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1997
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