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dc.contributor.authorRudraswami, N.G.
dc.contributor.authorGenge, M.J.
dc.contributor.authorMarrocchi, Y.
dc.contributor.authorVilleneuve, J.
dc.contributor.authorTaylor, S.
dc.date.accessioned2020-12-31
dc.date.accessioned2021-02-09T10:13:13Z
dc.date.available2020-10-01
dc.date.available2021-02-09T10:13:13Z
dc.date.issued2020
dc.identifier.citationJournal of Geophysical Research: Planets, vol.125(10); 2020; Article no: e2020JE006414
dc.identifier.issn2169-9097
dc.identifier.otherhttps://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020JE006414
dc.identifier.urihttps://doi.org/10.1029/2020je006414
dc.identifier.urihttp://drs.nio.org/drs/handle/2264/8419
dc.descriptionIF2019 - 3.713
dc.description.abstractCosmic spherules are micrometeorites that melt at high altitude as they enter Earth’s atmosphere and their oxygen isotope compositions are partially or completely inherited from the upper atmosphere, depending on the amount of heating experienced and the nature of their precursor materials. In this study, the three oxygen isotope compositions of 137 cosmic spherules are determined using 277 insitu analyses by ion probe. Our results indicate a possible correlation between an increasing average δ 18O compositions of silicate dominated (S-type) spherules along the series scoriaceous<porphyritic<barred<cryptocrystalline<glass<CAT spherules (~12, 20, 22, 25, 26 and 50‰). This is consistent with the evolution of oxygen isotopes by mass fractionation owing to increased average entry heating thus suggests mass fractionation dominates changes in isotopic composition, with atmospheric exchange being less significant. The  17O values of spherules, therefore, are mostly preserved and suggest that ~80% of particles are samples of C-type asteroids. The genetic relationships between different S-types can also be determined with scoriaceous, barred and cryptocrystalline-spherules mostly having low  17O values (≤0‰) mainly derived from CC-like sources, whilst porphyritic spherules mostly have positive  17O (>0‰) are largely derived from ordinary chondrite (OC)-like sources related to S(IV)-type asteroids. Glass and CAT-spherules have variable  17O values indicating they formed by intense entry heating of both CC and OC-like materials. I-type cosmic spherules have a narrow range of δ17O (~20–25‰) and δ18O (~38–48‰) values, with  17O (~0‰) suggesting their oxygen is obtained entirely from the Earth’s atmosphere, albeit with significant mass fractionation owing to evaporative heating. Finally, G-type cosmic spherules have unexpected isotopic compositions demostrate little mass-fractionation from a CC-like source. The results of this study provide a vital assessment of the wider population of extraterrestrial dust arriving at the Earth.
dc.languageen
dc.publisherAmerican Geophysical Union (AGU)
dc.relation.ispartofJ Geophys Res Planets
dc.relation.isreferencedbySCI
dc.rightsOnly the author version of the copright reserved papers uploaded. Contact drs@nio.org for any complaints regarding copyright violations
dc.titleThe Oxygen Isotope Compositions of Large Numbers of Small Cosmic Spherules: Implications for Their Sources and the Isotopic Composition of the Upper Atmosphere
dc.typeJournal Article
dc.affiliation.authorCSIR-National Institute of Oceanography, Dona Paula, Goa, India


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