Carbon isotope fractionation between graphite and diamond during shock experiments

available online at http://meteoritics.org 1255 © Meteoritical Society, 2003. Printed in USA. Carbon isotope fractionation between graphite and diamond during shock experiments Teruyuki MARUOKA,1†* Christian KOEBERL,1 Jun-ichi MATSUDA,2 and Yasuhiko SYONO3 1Department of Geological Sciences, University of Vienna, Althanstrasse 14, A-1090, Vienna, Austria 2Department of Earth and Science, Graduate School of Science, Osaka University, Toyonaka, Osaka 560–0043, Japan 3Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980, Japan †Present Address: Laboratory for Space Sciences, Physics Department, Washington University, 1 Brookings Drive, St. Louis, Missouri 63130–4899 *Corresponding author. E-mail: [email protected] (Received 26 January 2003; revision accepted 22 July 2003) Abstract–Carbon isotopic compositions were measured for shock-produced diamond and shocked graphite formed at peak pressures ranging from 37 to 52 GPa. The d13C values of diamonds producedCarbon isotopic compositions were measured for shock-produced diamond and shocked graphite formed at peak pressures ranging from 37 to 52 GPa. The d13C values of diamonds produced in a sealed container were generally lower than that of the initial graphite. The differences in the carbon isotopic composition between initial graphite and shocked graphite/diamond may reflect kinetic isotopic fractionation during the oxidation of the graphite/diamond and/or analytical artifacts possibly induced by impurities in the samples. The pressure effect on the isotopic fractionations between graphite and diamond can be estimated from the d13C values of impurity-free diamonds produced using a vented container from which gases, including oxygen, in pore spaces escaped during or after the diamond formation (e.g., 0.039 ± 0.085‰ at a peak pressure of 52 GPa). Any isotopic fractionation induced by shock conversion of graphite to diamond is too small to be detected in natural shock-induced diamond-graphite systems related to terrestrial impact cratering processes.