HR: 15:28h
AN: MR23D-10 INVITED    [Abstracts]
TI: Indications of crustal carbon in lower-mantle Juina diamond as revealed by FIB/TEM and NanoSIMS investigations.
AU: * Wirth, R
EM: wirth@gfz-potsdam.de
AF: GeoForschungsZentrum Potsdam, Experimental Geochemistry Telegrafenberg, Potsdam, Bra D 14473, Germany
AU: Pinti, D
EM: pinti.daniele@uquam.ca
AF: Université du Québec à Montréal, Département des Sciences de la Terre et de l'Atmosphère 201, Avenue du Université du Québec à Montréal et GEOTOP-UQAM-McGill 201, Avenue du Président-Kennedy, Montreal, Qc Canada H2X, Canada
AU: Sano, Y
EM: ysano@ori.u-tokyo.ac.jp
AF: University of Tokyo, Center for Advanced Marine Research, Tokyo, 164-8639, Japan
AU: Takahata, N
EM: ysano@ori.u-tokyo.ac.jp
AF: University of Tokyo, Center for Advanced Marine Research, Tokyo, 164-8639, Japan
AU: Kaminsky, F
EM: kmdiamond@shaw.ca
AF: KMD DIAMOND EXPLORATION, 2446 Shadbolt Lane, Vancouver, BC V7S 3j1, Canada
AB: Indications of crustal carbon in lower-mantle Juina diamond as revealed by FIB/TEM and NanoSIMS investigations. R. Wirth, D.L. Pinti, Y. Sano, N. Takahata, F. Kaminsky Superdeep diamonds from Juina (Mato Grosso, Brazil) contain inclusions such as Fe-periclase, Ca-Si walstromite, majoritic garnet (Kaminsky et al., 2001) and most recently a hydrous aluminium silicate phase "Phase Egg" was found (Wirth et al. 2007). Phase Egg in diamond might suggest that crustal material has been subducted to a depth of the lower Transition Zone. The present paper demonstrates how the combination of Focused Ion Beam (FIB) specimen preparation combined with TEM and NanoSIMS can provide a comprehensive data set from a TEM foil with the dimensions of 15 x 10 x 0.200 micrometer. TEM investigation of the foil revealed the presence of three phases: diamond host – carbonate single crystal – ilmenite nanocrystal – amorphous quench phase. The carbonate is composed of Mg 45.4 at. %, Ca 49.8 at. %, Fe 4.3 at. %, Mn 0.2 at. % and Sr 0.2 at. %. The amorphous quench phase contains Si – Zr – K. The carbon and nitrogen isotopic composition of the diamond was analyzed from the same TEM foil against internal standard (carbonado diamond GM02 from Brazil) with a Camaca NanoSIMS 50. A 13 spot analyses for the carbon isotopic composition and the N content were measured following two precise transects across the sample. The δ13-C of the diamond varies between -13.9 ± 1.9 ‰ and -25.1± 1.8 ‰. The δ13-C values plotted against the C/N ratios suggest the occurrence of two carbon sources. The first source shows lower C/N ratio and enriched δ13-C (- 14 ‰). The second source of carbon shows higher C/N ratio and depleted δ13-C values (-25 ‰). The occurrence of predominantly depleted δ13-C values (-14 to -25 ‰) suggests that this diamond formed from or contains partially carbon from biological origin. A recent paper supports this idea that reports carbonate inclusions in diamonds from the same locality (Juina, Brazil) thus indicating that the Earth's global CO2-cycle has an ultra-deep extension (Brenker et al., 2007). References Brenker, F.E., Vollmer, C., Vincze, L., Vekemans, B., Szymanski, A., Janssens, K., Szaloki, I, Nasdala, L., Joswig. W., Kaminsky, F. (2007) Carbonates from the lower part of transition zone or even the lower mantle. EPSL, doi: 10.1016/j.epsl.2007.02.038. Kaminsky, F.V., Zakharchenko, O.D., Davies, R., Griffin, W.L., Shiryaev, A.A. (2001) Superdeep diamonds from the Juina area, Mato Grosso State, Brazil, Contributions to Mineralogy and Petrology 140(5), 734-753. Wirth, R., Vollmer, C., Brenker, F., Matsyuk, S., Kaminsky, F. (2007) Inclusions of nanocrystalline hydrous aluminium silicate "Phase Egg" in superdeep diamonds form Juina (Mato Grosso State, Brazil). EPSL, 259, 384- 399.
DE: 1025 Composition of the mantle
DE: 1042 Mineral and crystal chemistry (3620)
DE: 3621 Mantle processes (1038)
DE: 3994 Instruments and techniques
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting