Header
Accueil du site > Publications > The oxygen isotope compositions of large numbers of small cosmic spherules (...)

The oxygen isotope compositions of large numbers of small cosmic spherules : Implications for their sources and the isotopic composition of the upper atmosphere

Rudraswami, N.G. ; Genge, M.J. ; Marrocchi, Y. ; Villeneuve, J. ; Taylor, S., JGR Planets

The oxygen isotope compositions of large numbers of small cosmic spherules : Implications for their sources and the isotopic composition of the upper atmosphere

Rudraswami, N.G. ; Genge, M.J. ; Marrocchi, Y. ; Villeneuve, J. ; Taylor, S.

Journal of Geophysical Research : Planets, 2020, 125, e2020JE006414

Abstract :

Cosmic 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 in situ analyses by ion probe. Our results indicate a possible correlation between increasing average δ18O compositions of silicate -dominated (S-type) spherules along the series scoriaceous < porphyritic 0‰) and 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 signicant mass fractionation owing to evaporative heating. Finally, G-type cosmic spherules have unexpected isotopic compositions and demonstrate 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 on Earth.

Voir en ligne : https://doi-org.insu.bib.cnrs.fr/10...




publié mardi 6 octobre 2020