HR: 15:20h
AN: V43E-06    [Abstracts]
TI: Infrared and Raman spectroscopic observations on Central African carbonado and the implication to its origin
AU: * Kagi, H
EM: kagi@eqchem.s.u-tokyo.ac.jp
AF: Geochemical Laboratory, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan
AU: Fukura, S
EM: fukura@eqchem.s.u-tokyo.ac.jp
AF: Geochemical Laboratory, Graduate School of Science, University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan
AB: Carbonado diamonds from the Central African Republic (CAR) were investigated by means of spectroscopic observations. Raman spectra for the polished section of carbonado revealed that the surface of the sample gave the average Raman frequency at 1333.0 cm^-1, while 10 micrometer below the sample surface gave the bimodal distribution of Raman frequency with the average at 1333.5 cm^-1. These contrastive results indicate that the inside of carbonado retain the considerable residual pressure. The maximum residual pressure detected in this study from the 10 micrometer subsurface was 0.49 GPa. From infrared (IR) absorption spectra for crushed carbonado samples, no absorption due to diamond was observed because absorption bands due to mineral and fluid inclusions were too strongly observed. In contrast, the acid leaching treatment on the crushed grains gave rise to the observations of IR bands assignable to intrinsic diamond vibration and nitrogen impurity in diamonds. Nitrogen atoms in the CAR carbonado were not much aggregated and the extent of aggregation was intermediate between type Ib and type IaA. IR absorption bands from liquid water and carbonate were ubiquitously observed for the chemically treated samples. This suggests that the CAR carbonado samples contain fluid inclusion and are similar to the diamonds containing mantle-derived fluids. Overall, the experimental results obtained in the present study suggests that the CAR carbonado originated from some rapid heating event with a presence of fluid in the mantle and subsequent rapid cooling before aggregating impurity nitrogen in the diamond lattice.
DE: 1038 Mantle processes (3621)
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3630 Experimental mineralogy and petrology
DE: 3652 Pressure-temperature-time paths
DE: 3934 Optical, infrared, and Raman spectroscopy
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting