Extreme oxygen isotope ratios in the early solar system

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doi: 10.1038/nature03947
Authors:Aléon, Jérôme; Robert, François; Duprat, Jean; Derenne, Sylvie
Author Affiliations:Primary:
Centre de Recherches Pétrographiques et Géochimiques, Vandoeuvre les Nancy, France
Museum National d'Histoire Naturelle, France
Centre de Spectrométrie Nucléaire et de Spectrométrie en Masse, France
Ecole Nationale Supérieure de Chimie de Paris, France
Volume Title:Nature (London)
Source:Nature (London), 437(7057), p.385-388. Publisher: Macmillan Journals, London, United Kingdom. ISSN: 0028-0836
Publication Date:2005
Note:In English. 30 refs.; illus., incl. 1 table
Summary:The results are summarized of ion imaging of acid insoluble matter (IOM) isolated from the Murchison meteorite, and ion images are presented of 16O, 17O, 18O and 26Si in organic pellets. Systematic O and Si isotope mapping by ion microprobe identified 31 Si-rich grains with extreme 17O and 18O excesses within the IOM. 17O/16O ratios are plotted against 18O/16O ratios for Si-rich grains, presolar oxides and silicates, presolar graphites and terrestrial olivine. An SEM micrograph illustrates euhedral Si-rich grains and energy-dispersive X-ray spectra. These ratios define a mixing line between the solar and the most extreme values and could result from mixing within the ion probe spot, of O from the grains and from IOM, or from the indigenous O isotopic composition of the grains. Whatever the exact size of these effects, the results show that the mixing occurs with a single heavy O reservoir with 17O/16/O ≥ 7.7 X 10-2, 18O/16O ≥ 1.2 X 10-1 and 18O/17O ≤ 1.5. Large O isotopic anomalies in meteoritic grains are commonly attributed to stellar nucleosynthesis, but the association of large 17O and 18O excessses together with the solar Si isotope composition is a challenge to current stellar models. It is suggested that O isotopic similarities between the present Si-rich grains and of CO2 in HR 4049-a post- asymptotic giant branch star entering the planetary nebula phase, could indicate a widespread selective chemical trapping of a nucleosynthetic reservoir in stellar ejecta/outflows. Irradiation of the circumsolar gas by high-energy particles accelerated during an active phase of the young Sun is favoured as a possible mechanism. [R.K.H.]
Sections:Lunar and planetary studies
Subsections:Analytical geochemistry
Subjects:Carbonaceous chondrites; Chondrites; CM chondrites; Cosmochemistry; Gases; Isotope ratios; Isotopes; Meteorites; Murchison Meteorite; O-17/O-16; O-18/O-16; Organic compounds; Oxygen; Parent bodies; Planetology; Reconstruction; Silicon; Solar system; Stable isotopes; Stony meteorites
Abstract Numbers:05M/3441
Record ID:2006007543
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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