<?xml version='1.0' encoding='utf-8'?>
<oai_dc:dc xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:oai_dc="http://www.openarchives.org/OAI/2.0/oai_dc/" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.openarchives.org/OAI/2.0/oai_dc/ http://www.openarchives.org/OAI/2.0/oai_dc.xsd">
  <dc:contributor>Walter D. Mooney</dc:contributor>
  <dc:contributor>James H. Luetgert</dc:contributor>
  <dc:contributor>Nikolas I. Christensen</dc:contributor>
  <dc:creator>G. Musacchio</dc:creator>
  <dc:date>1997</dc:date>
  <dc:description>&lt;div class="article-section__content en main"&gt;&lt;p&gt;We use the ratios between&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;P&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;S&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;wave velocities (V&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;), 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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;increasing with depth from 1.64 to 1.84; there is a clear distinction between the Grenville Province (average V&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;=1.81) and the Appalachian Province (average V&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;=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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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&lt;sub&gt;&lt;i&gt;P&lt;/i&gt;&lt;/sub&gt;/V&lt;sub&gt;&lt;i&gt;S&lt;/i&gt;&lt;/sub&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;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.&lt;/p&gt;&lt;/div&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1029/96JB03737</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>American Geophysical Union</dc:publisher>
  <dc:title>Composition of the crust in the Grenville and Appalachian Provinces of North America inferred from VP/VS ratios</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>