TERRAPUB Geochemical Journal
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Geochemical Journal, Vol. 50 (No. 4), pp. e7-e12, 2016
doi:10.2343/geochemj.2.0427

EXPRESS LETTER

Micron-scale δ13C determination by NanoSIMS in a Juina diamond with a carbonate inclusion

Daniele L. Pinti,1* Akizumi Ishida,2 Naoto Takahata,2 Yuji Sano,2 Hélène Bureau3 and Pierre Cartigny4

1GEOTOP and Département des sciences de la Terre et de l'atmosphère, Université du Québec à Montréal, CP 8888 succ. Centre-Ville, Montréal, QC, H3C 3P8, Canada
2Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-8564, Japan
3Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Sorbonne Universités - UPMC Univ. Paris 06, CNRS UMR 7590 & Muséum National d'Histoire Naturelle, IRD UR 206, 75252 Paris Cedex 05, France
4Laboratoire de Géochimie des Isotopes Stables, Institut de Physique du Globe de Paris, Université Paris Diderot, CNRS, UMR 7154, Sorbonne Paris-Cité, 75238 France

(Received April 1, 2016; Accepted June 4, 2016; Online published June 21, 2016)

Abstract: Juina diamonds present a wide spectrum of mineral inclusions, covering both peridotitic and eclogitic composition. Among the most rare inclusions, carbonates are interpreted as an evidence of deep recycling of sedimentary carbon into the transition zone or the lower mantle. Yet, the δ13C values measured in three FIB-TEM foils by NanoSIMS 50 of an alluvial diamond with a carbonate inclusion range between −8.85 ± 1.32‰ and −2.31 ± 1.88‰ with a mean total value of −5.0 ± 2.3‰. These values are in the range of typical mantle carbon, as measured in diamonds of peridotitic paragenesis. Similar δ13C values from −8.5 to −4.4‰ are reported in literature for five other Juina diamonds with carbonate inclusions. We can postulate either that the diamond is peridotitic and carbonate precipitated from fluids and survived to the reduction to diamond or that formed from reduction of carbonatitic melts in the upper mantle, percolating through eclogite.
Key words: sub-lithospheric diamonds, Juina, carbonate, lower mantle, peridotite, eclogite


*Corresponding author E-mail: pinti.daniele@uqam.ca


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