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<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>J. Wright Horton, Jr.</dc:contributor>
  <dc:contributor>Avery A. Drake Jr.</dc:contributor>
  <dc:contributor>R. P. Wintsch</dc:contributor>
  <dc:contributor>C.M. Fanning</dc:contributor>
  <dc:contributor>K. Yi</dc:contributor>
  <dc:creator>John N. Aleinikoff</dc:creator>
  <dc:date>2004</dc:date>
  <dc:description>&lt;p&gt;&lt;span&gt;The&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Baltimore&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Gneiss&lt;/span&gt;&lt;span&gt;, exposed&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;antiforms&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the eastern&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Maryland&lt;/span&gt;&lt;span&gt;&amp;nbsp;Piedmont, consists of a suite of felsic and mafic gneisses of&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Mesoproterozoic&lt;/span&gt;&lt;span&gt;&amp;nbsp;age. Zircons from the felsic gneisses are complexly zoned, as shown&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;cathodoluminescence&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;imaging&lt;/span&gt;&lt;span&gt;; most&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;zircon&lt;/span&gt;&lt;span&gt;&amp;nbsp;grains have&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;multiple&lt;/span&gt;&lt;span&gt;&amp;nbsp;overgrowth zones, some of which are adjacent and parallel to elongate cores. Sensitive high-resolution ion microprobe (&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;SHRIMP&lt;/span&gt;&lt;span&gt;) analyses of oscillatory-zoned cores indicate that the volcanic protoliths of the felsic gneisses crystallized at ca. 1.25 Ga. These rocks were subsequently affected by at least three&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Mesoproterozoic&lt;/span&gt;&lt;span&gt;&amp;nbsp;growth&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;events&lt;/span&gt;&lt;span&gt;, at ca. 1.22, 1.16, and 1.02 Ga. Foliated biotite granite intruded the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Baltimore&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Gneiss&lt;/span&gt;&lt;span&gt;&amp;nbsp;metavolcanic sequence at ca. 1075 Ma. The Slaughterhouse Granite (renamed herein) also is&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Mesoproterozoic&lt;/span&gt;&lt;span&gt;, but extremely discordant U-Pb data from high-U, metamict zircons preclude calculating a precise age. The 1.25 Ga rocks of the&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Baltimore&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Gneiss&lt;/span&gt;&lt;span&gt;&amp;nbsp;are coeval with rocks emplaced&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;the Grenville Province during the Elzevirian orogeny, and the 1.22 Ga&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;zircon&lt;/span&gt;&lt;span&gt;&amp;nbsp;overgrowths are coincident with a later stage of this&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;event&lt;/span&gt;&lt;span&gt;. Younger&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;zircon&lt;/span&gt;&lt;span&gt;&amp;nbsp;overgrowths formed during the Ottawan phase of the Grenville orogeny. Backscattered electron&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;imaging&lt;/span&gt;&lt;span&gt;&amp;nbsp;of titanites from felsic gneisses and foliated biotite granite reveals that many of the grains contain cores, intermediate mantles, and rims. Electron microprobe traverses across zoned grains show regular variations&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;in&lt;/span&gt;&lt;span&gt;&amp;nbsp;composition.&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;SHRIMP&lt;/span&gt;&lt;span&gt;&amp;nbsp;ages for&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;titanite&lt;/span&gt;&lt;span&gt;&amp;nbsp;from the foliated biotite granite are 374 ± 8, 336 ± 8, and 301 ± 12 Ma. The ca. 374 Ma age suggests growth of&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;titanite&lt;/span&gt;&lt;span&gt;&amp;nbsp;during a thermal&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;event&lt;/span&gt;&lt;span&gt;&amp;nbsp;following the Acadian orogeny, whereas the late&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;Paleozoic&lt;/span&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;span class="ScopusTermHighlight"&gt;titanite&lt;/span&gt;&lt;span&gt; growth ages may be due to greenschist-facies replacement reactions associated with Alleghanian metamorphism and deformation.&amp;nbsp;&lt;/span&gt;&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1130/0-8137-1197-5.411</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Geological Society of America</dc:publisher>
  <dc:title>Deciphering multiple Mesoproterozoic and Paleozoic events recorded in zircon and titanite from the Baltimore Gneiss, Maryland: SEM imaging, SHRIMP U-Pb geochronology, and EMP analysis</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>