Oxygen isotope heterogeneities in the earliest protosolar gas recorded in a meteoritic calcium-aluminum-rich inclusion

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doi: 10.1016/j.epsl.2007.09.003
Authors:Aléon, Jérôme; El Goresy, Ahmed; Zinner, Ernst
Author Affiliations:Primary:
Centre de Recherches Petrographiques et Géochimiques, Vandoeuvre-lès-Nancy, France
Universität Bayreuth, Federal Republic of Germany
Washington University, United States
Volume Title:Earth and Planetary Science Letters
Source:Earth and Planetary Science Letters, 263(1-2), p.114-127. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012-821X
Publication Date:2007
Note:In English. Supplemental information/data is available in the online version of this article. 49 refs.; illus., incl. 3 tables
Summary:Combined petrologic, oxygen and magnesium isotopic and trace element analyses of a compound calcium-aluminum-rich inclusion (CAI) from the Efremovka reduced CV3 carbonaceous chondrite reveal that it consists of a Mg-rich, 16O-rich xenolithic CAI, previously altered in the nebula, that impacted an extensively molten, 16O-depleted, type A host CAI shortly before the end of the host's crystallization. Convoluted regions in the xenolith were probably formed by rapid crystallization of the partial melt produced during impact. Oxygen isotopic ratios in the host CAI are correlated both with melilite chemistry and location in the inclusion. The region immediately inside the Wark-Lovering rim of the CAI consists of 16O-rich gehlenite with Δ17O ranging down to -20 ppm but melilite becomes progressively 16O-poor (Δ17O∼0 ppm) and Mg-rich towards the interior. In the absence of Mg isotopic fractionation, this variation is best attributed to O isotopic exchange between the nebular gas and the partially molten inclusion during its crystallization. This event lasted less than 200 h, which implies that the host CAI was transported between two nebular reservoirs with distinct O isotopic compositions during this time. Examination of possible transport mechanisms suggests that the transport occurred over a distance of less than 1 astronomical unit. The close-to-canonical 26Al/27Al ratio of 4.1×10-5 determined from both inclusions implies that at most 670,000 yr after the birth of the Solar System, the 16O-rich reservoir was spatially limited and an 16O-poor reservoir with typical planetary isotopic composition was available for planet formation. Abstract Copyright (2007) Elsevier, B.V.
Sections:Geochemistry; Meteorites and tektites
Subjects:Al-27/Al-26; Alkaline earth metals; Aluminum; Calcium-aluminum inclusions; Carbonaceous chondrites; Chondrites; CV chondrites; Efremovka Meteorite; Fractional crystallization; Gases; Heterogeneity; Inclusions; Ion probe data; Isotope ratios; Isotopes; Magnesium; Mass spectra; Melilite; Melilite group; Metals; Meteorites; Mg-26/Mg-24; O-17/O-16; O-18/O-16; Orthosilicates; Oxygen; Planetology; Radioactive isotopes; Refractory materials; Silicates; Solar nebula; Sorosilicates; Spectra; Stable isotopes; Stony meteorites; Trace elements; Xenoliths; Protosolar nebula
Abstract Numbers:07M/4643
Record ID:2008079976
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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