<?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>David S. Powars</dc:contributor>
  <dc:contributor>Gregory Gohn</dc:contributor>
  <dc:creator>J. Wright Horton, Jr.</dc:creator>
  <dc:date>2005</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;The USGS-NASA&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;corehole at&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Hampton&lt;/span&gt;&lt;span&gt;, Va., was drilled&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;2000 and was the first corehole to reach&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;coastal&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;plain&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;basement&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the late Eocene&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Chesapeake&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Bay&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;structure&lt;/span&gt;&lt;span&gt;. The&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;core&lt;/span&gt;&lt;span&gt;&amp;nbsp;provided samples of granite that had been concealed by 626.3 meters (2,054.7 feet) of preimpact, synimpact, and postimpact sediments. The granite, here named the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;Granite, is pale red, medium grained, massive, and homogeneous&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;composition and fabric. It has a peraluminous composition (alumina saturation index 1.1) and a seriate-inequigranular, hypidiomorphic, isotropic fabric. A pervasive secondary mineral assemblage of chlorite + albite + clinozoisite is consistent with either deuteric alteration or lower greenschist-facies metamorphism. Chlorite, the principal mafic mineral, occurs as tabular masses that suggest pseudomorphous replacement of biotite. The top of the granite is weathered but not saprolitized and is nonconformably overlain by Lower Cretaceous clastic sediments. A SHRIMP&amp;nbsp;&lt;/span&gt;&lt;sup&gt;206&lt;/sup&gt;&lt;span&gt;Pb/&lt;/span&gt;&lt;sup&gt;238&lt;/sup&gt;&lt;span&gt;U weighted average zircon&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;age&lt;/span&gt;&lt;span&gt;&amp;nbsp;of 612±10 Ma (2σ) indicates Neoproterozoic crystallization of the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;Granite. The&amp;nbsp;&lt;/span&gt;&lt;sup&gt;40&lt;/sup&gt;&lt;span&gt;Ar/&lt;/span&gt;&lt;sup&gt;39&lt;/sup&gt;&lt;span&gt;Ar ages of microcline and plagioclase are consistent with regional cooling and uplift after the late Paleozoic Alleghanian orogeny. Zircon and apatite fission-track cooling ages of 375±44 Ma and 184±32 Ma (2σ), respectively, indicate no discernible&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;-related&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;thermal&lt;/span&gt;&lt;span&gt;&amp;nbsp;disturbance at the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;corehole location&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the annular trough of the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;structure&lt;/span&gt;&lt;span&gt;&amp;nbsp;about 19 kilometers (12 miles) outside the margin of the central crater. Modeling the apatite fission-track data places upper limits on the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;-related heating at this location. For an&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;-related&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;thermal&lt;/span&gt;&lt;span&gt;&amp;nbsp;disturbance equivalent to a modeled&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;thermal&lt;/span&gt;&lt;span&gt;&amp;nbsp;spike having a duration of 1 to 0.1 million years, temperatures&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;this part of the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;structure&lt;/span&gt;&lt;span&gt;&amp;nbsp;could not have been higher than about 100°C-120°C. Most fractures, faults, and veins&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Langley&lt;/span&gt;&lt;span&gt;&amp;nbsp;Granite contain lower greenschist-facies minerals and are inferred to predate the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;. No shock-metamorphosed minerals or other features clearly attributable to the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;&amp;nbsp;were found&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the granite. Studies of the granite provide a glimpse into the nature of crystalline terranes beneath the Atlantic&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Coastal&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Plain&lt;/span&gt;&lt;span&gt;&amp;nbsp;and&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Chesapeake&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Bay&lt;/span&gt;&lt;span&gt;&amp;nbsp;and provide limits on the geographic extent of&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;impact&lt;/span&gt;&lt;span&gt;-generated shock and&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;thermal&lt;/span&gt;&lt;span&gt;&amp;nbsp;effects.&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.3133/pp1688B</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>U.S. Geological Survey</dc:publisher>
  <dc:title>Petrography, structure, age, and thermal history of granitic coastal plain basement in the Chesapeake Bay impact structure, USGS-NASA Langley core, Hampton, Virginia</dc:title>
  <dc:type>reports</dc:type>
</oai_dc:dc>