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

N. G. RUDRASWAMI1, Yves MARROCCHI2, M. SHYAM PRASAD1, D. FERNANDES1,Johan VILLENEUVE2, and S. TAYLOR3
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13281]
1National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, Goa 403004, India
2CRPG, CNRS, Universite de Lorraine, UMR 7358, Vandoeuvre-les-Nancy F-54501, France
3Cold Regions Research and Engineering Laboratory, 72 Lyme Road, Hanover, New Hampshire 03755–1290, USA
Published by arrangement with John Wiley & Sons

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‰, most of them being similar to those of chromites from ordinary chondrites. The oxygen isotopic compositions of olivine, considered as a proxy of chromite in chromite‐bearing micrometeorites where chromite is too small to be measured in ion microprobe have Δ17O values suggesting a principal relationship to ordinary chondrites 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 a small fraction from carbonaceous chondrites, unlike other micrometeorites deriving largely from carbonaceous chondrites.

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