MC-HR-SIMS oxygen isotope analysis of ferropericlase inclusions in diamond

R. B. Ickert, R. A. Stern, T. Stachel

Research output: Contribution to journalMeeting abstract

Abstract

Ferropericlase (Mg, Fe)O is an important terrestrial mineral. While relatively rare in the crust, it constitutes approximately 17% by volume of the lower mantle, from ~660km to ~2900km. Importantly, the assemblage of ferropericlase and perovskite (which together are diagnostic of a lower mantle origin) are rarely found together as inclusions in diamond and provide our only solid samples of a region that occupies over 50% of Earths volume [1].

Studies of these ultra-deep diamond inclusions have shown that the periclase inclusions can have a variable Mg#, and have demonstrated the presence of Eu anomalies in coexisting perovskite [2-3]. This has led some workers to suggest that the ultra-deep mineral assemblages trapped in the
diamond formed from subducted crust that has passed through the transition zone and into the lower mantle [3]. If verified, this would provide an important geochemical verification of whole mantle convection.

Oxygen isotope ratios of crustal rocks can be distinctly different those of the mantle (δ18OVSMOW values of ca. 5.5‰) and can therefore provide a crucial test of the crustal or mantle heritage of ferropericlase inclusions. Diamond inclusions of ferropericlase are <100μm in size and therefore best analysed by microbeam methods. We have performed preliminary experiments on the 18O/16O measurement of synthetic and natural crustal periclase on the newly installed Cameca IMS1280 multicollector secondary ion mass spectrometer (MC-SIMS) at CCIM,. The SIMS analytical methods largely follow established procedures, using Cs- primary ions, normal incidence electron gun, and multi-collection on faraday cups. Synthetic and natural RM’s are being characterized by laser fluorination. Preliminary analysis shows that internal spot errors of <0.1‰ (1$) for 18O/16O are readily achieved. Spot-to-spot reproducibility and potential matrix effects due to varying Mg#s will be examined.
Original languageEnglish
Article number3
Pages (from-to)A442-A442
Number of pages1
JournalGeochimica et Cosmochimica Acta
Volume74
Issue number12, Supplement
DOIs
Publication statusPublished - Jun 2010
Externally publishedYes
EventGoldschmidt Conference (20th : 2010) - Knoxville, United States
Duration: 13 Jun 201018 Jun 2010

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