<?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>J. R. O’Neil</dc:contributor>
  <dc:creator>J.W. Valley</dc:creator>
  <dc:date>1981</dc:date>
  <dc:description>&lt;p&gt;The fractionation of&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;13&lt;/sup&gt;C between calcite and graphite, Δ(Cc-Gr). is consistently small (2.6–4.8 permil) in 34 assemblages from upper amphibolite- and granulite-facies marbles of the Grenville Province. In 25 samples from the Adirondack Mountains, New York, it decreases regularly with increasing metamorphic temperature. The fractionations are independent of absolute δ&lt;sup&gt;13&lt;/sup&gt;C values of calcite (−2.9 to +5.0). For&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;T&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;= 600–800°&lt;i&gt;C&lt;/i&gt;, the Adirondack data are described by&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;Δ&lt;/i&gt;(&lt;i&gt;Cc&lt;/i&gt;-&lt;i&gt;Gr&lt;/i&gt;) = −0.00748&lt;i&gt;T&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;(°&lt;i&gt;C&lt;/i&gt;) + 8.68. This good correlation between Δ and&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;i&gt;T&lt;/i&gt;&lt;span&gt;&amp;nbsp;&lt;/span&gt;suggests that carbon isotope equilibrium was attained in these high-grade marbles and that the theoretical calculations of this fractionation by Bottinga are approximately 2 permil too large in this temperature range. Because of the relatively high temperature sensitivity suggested by these results and by Bottinga's calculations, and the pressure independence of isotope fractionation, Δ(Cc-Gr) may provide a very good thermometer for high-grade marbles.&lt;/p&gt;&lt;p&gt;Comparison of this field calibration for Δ(Cc-Gr) vs temperature with results from other terranes supports the utility of Δ(Cc-Gr) for geothermometry and suggests that graphite is much more sluggish to exchange than calcite, that exchange between calcite and graphite occurs at temperatures as low as 300°C, and that equilibrium may normally be attained only when peak metamorphic temperatures are greater than 500–600°C.&lt;/p&gt;&lt;p&gt;Because&lt;span&gt;&amp;nbsp;&lt;/span&gt;&lt;sup&gt;13&lt;/sup&gt;C exchange is an unavoidable metamorphic process at temperatures above 300°C, high values of δ&lt;sup&gt;13&lt;/sup&gt;C(Gr) in moderate- to high-grade carbonate-bearing rocks do not provide a sufficient criterion to infer an abiogenic origin for the graphite.&lt;/p&gt;</dc:description>
  <dc:format>application/pdf</dc:format>
  <dc:identifier>10.1016/0016-7037(81)90249-0</dc:identifier>
  <dc:language>en</dc:language>
  <dc:publisher>Elsevier</dc:publisher>
  <dc:title>13C 12C exchange between calcite and graphite: A possible thermometer in Grenville marbles</dc:title>
  <dc:type>article</dc:type>
</oai_dc:dc>