HR: 1330h
AN: V22D-0620    [PDF]
TI: SIMS carbon isotope study of microdiamond in UHP dolomite marble from the Kokchetav Massif
AU: * Imamura, K
EM: imamura@toki.waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AU: Ogasawara, Y
EM: yoshi777@waseda.jp
AF: Department of Earth Sciences, Waseda University, 1-6-1 Nishiwaseda, Shinjuku-ku, Tokyo, 169-8050 Japan
AU: Yurimoto, H
EM: yuri@geo.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro-ku, Tokyo, 152-8550 Japan
AU: Kusakabe, M
EM: kusakabe@misasa.okayama-u.ac.jp
AF: Institute for Study of the Earth's Interior, Okayama University, 827 Misasacho yamada, Tohaku-gun, Tottori, 682-1093 Japan
AB: Carbon isotope of 10-20 micrometer-sized metamorphic diamond inclusions in garnet was analyzed with a SIMS at Tokyo Institute of Technology. The samples used for this SIMS analysis are UHP dolomite marble corrected at Kumdy-kol in the Kokchetav Massif, northern Kazakhstan. Typical microdiamond in this dolomite marble shows star-shaped morphology (S-type) measuring 10-20 $\mu$m in diameter and consists of single crystal core and polycrystalline rim having different orientations (Ishida et al., 2003). Cathode luminescence (CL) images and spectra of S-type microdiamonds also show the difference between core and rim; the peak intensity at 525 nm of the rim is significantly stronger than that of the core (Yoshioka et al., 2002). Their results in CL analysis supported the two-stage growth of S-type microdiamond in dolomite marble (Ishida et al., 2003). For the SIMS measurements, we prepared the samples in ordinary polished thin sections that were previously examined by other methods (e.g. CL). Three grains of S-type microdiamond and two grains of single crystal R-type diamond (single crystal with rugged surface, Ishida et al., 2003) are analyzed up to now. The ion beam spot of SIMS analysis is about 5 $\mu$mm in diameter. The analyzed spots were confirmed by secondary electron images after SIMS analysis. The sample of S-type microdiamond (no. XX01-1-13) showed $\delta$$^{13}$C values ranging from -13 to -9$\permil$ (average -10.4$\permil$) for the core, and from -21 to -15$\permil$ (average -17.2$\permil$) for the rim. Such heterogeneous $\delta$$^{13}$C distribution in S-type microdiamond was also detected in the other two samples that indicated significant gap of $\delta$$^{13}$C range; the sample no. XX01-1-12: -20 to -18$\permil$ (average -17.5$\permil$) and -27 to -22$\permil$ (average -23.9$\permil$), and the sample no. XX01-1-15: -18 to -16$\permil$ (average -17.1$\permil$) and ranging from -27 to -23$\permil$ (average -24.9$\permil$). Two independent analyses of the same sample (no. XX01-1-16) of R-type microdiamond show good reproducibility in $\delta$$^{13}$C values; analysis no. 1: -15 to -8$\permil$ (average -11.5$\permil$) and analysis no. 2: -13 to -9$\permil$ (average -11.0$\permil$). The other sample of R-type microdiamond (no. XX01-1-10) showed $\delta^{13}$C values ranging from -16 to -11$\permil$ (average -12.9$\permil$). Summarizing these carbon isotope data hitherto obtained strongly support two-stage growth of microdiamond in UHP dolomite marble in the Kokchetav Massif. References: Ishida, Ogasawara, Osumi \& Saito (2003) J. Metamorphic Geol. 21, 515-522 Yoshioka, Imamura \& Ogasawara (2002) EOS Transactions AGU, 83, F1403
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting