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Poster De Conférence Année : 2019

Si isotopes and small scale processes in olivine-hosted melt inclusions

Résumé

Melt inclusions are minute melts trapped during crystal growth [e.g., 1]. When trapped in euhedral olivine they are believed to represent the melt in which olivine grew[1], despite some post-entrapment modifications [e.g., 2, 3]. In this study, we analysed olivine hosted melt inclusions (OHMIs) in Mid-Ocean Ridge Basalts (MORBs) from two different locations on the Mid-Atlantic Ridge: FAMOUS and the 14° MAR triple junction (respectively Normal-MORB and Enriched-MORB).Silicon, as oxygen,is a major element inolivines and it diffusesslowly in dry basaltic melt [4]. Both isotope systems (O and Si) do not fractionate during melting [e.g., 5]. The isotopic ranges reported for bulk MORBs are narrow(<0.5‰)[e.g., 6, 7].Thus, we do not expectδ30Siand δ18Ovariability in OHMIs. However, previous analyses ofδ18Oin these OHMIs showup to 2.5‰ variation (8 times the analytical error)in each sample[8]. Any difference or similarity betweenthe δ30Si and δ18O signaturesinthe OHMIs would give valuable insight on the process responsible for the δ18Ovariation in the OHMIs.Silicon isotopes in OHMIs were measured by ion probe. OHMIs from the two samples displaysimilar δ30Sivalues, rangingfrom 0.08±0.23‰to 2.8±0.32‰for the N-MORB, and from 0.51±0.34‰to 2.8±0.31‰for the E-MORB(2se).The variation is larger than the accuracy (~0.4‰).δ18Oand δ30Sidisplay a slight positive trend. While theaverage δ18Ovalue in the OHMIs from the N-MORB sample is similar to the values previoulsy reported for bulk MORBs [6], the average δ30Siis muchhigher, and similar for both of our samples.Such high valuesare not representative of any high temperature terrestrial reservoirs. The large δ30Sioffset with bulk MORBsand the large variation within the OHMI population thus most likelyreflect either a localizedor OHMIs-specific process(e.g. boundary layer or local dissolution).
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Dates et versions

hal-02357724 , version 1 (10-11-2019)

Identifiants

  • HAL Id : hal-02357724 , version 1

Citer

Clémence Lelay, Anne-Sophie Bouvier, Estelle F. Rose-Koga, Muriel Laubier, Pierre Schiano, et al.. Si isotopes and small scale processes in olivine-hosted melt inclusions. Goldschmidt Conference, Aug 2019, Barcelona, Spain. Goldschmidt Conference abstract volume, 2019. ⟨hal-02357724⟩
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