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Oxygen isotopic and chemical composition of chromites in micrometeorites: Evidence of ordinary chondrite precursors

Abstract : We identified 66 chromite grains from 42 of ~5000 micrometeorites collected from Indian Ocean deep-sea sediments and the South Pole water well. To determine the chromite grains precursors and their contribution to the micrometeorite flux, we combined quantitative electron microprobe analyses and oxygen isotopic analyses by high-resolution secondary ion mass spectrometry. Micrometeorite chromite grains show variable O isotopic compositions with δ18O values ranging from –¬¬0.8 to 6.0‰, δ17O values from 0.3 to 3.6‰, and Δ17O values from –0.9 to 1.6‰, seems majority of them are similar to those of chromites from ordinary chondrites. The oxygen isotopic compositions of olivine as a proxy to the chromite in chromite-bearing micrometeorites where we could not measure chromite have Δ17O values suggesting largely related to ordinary chondritic with some having carbonaceous chondrite precursors. Furthermore, the chemical compositions of chromites in micrometeorites are close to those reported for ordinary chondrite chromites, but some contribution from carbonaceous chondrites cannot be ruled out. Consequently, carbonaceous chondrites cannot be a major contributor of chromite-bearing micrometeorites. Based on their oxygen isotopic and elemental compositions, we thus conclude with no ambiguity that chromite-bearing micrometeorites are largely related to fragments of ordinary chondrites with small fraction from carbonaceous chondrites, unlike other micrometeorites deriving largely from carbonaceous chondrites.
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Contributor : Yves Marrocchi Connect in order to contact the contributor
Submitted on : Sunday, November 10, 2019 - 12:54:24 PM
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N. G Rudraswami, Yves Marrocchi, M. Shyam Prasad, D. Fernandes, Johan Villeneuve, et al.. Oxygen isotopic and chemical composition of chromites in micrometeorites: Evidence of ordinary chondrite precursors. Meteoritics and Planetary Science, Wiley, 2019, 54 (6), pp.1347-1361. ⟨10.1111/maps.13281⟩. ⟨hal-02357526⟩



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