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26 Al- 26 Mg and 207 Pb- 206 Pb systematics of Allende CAIs: Canonical solar initial 26 Al/ 27 Al ratio reinstated

Jacobsen, Benjamin; Yin, Qing-zhu; Moynier, Frederic; Amelin, Yuri; Krot, Alexander; Nagashima, Kazuhide; Hutcheon, Ian D; Palme, Herbert

Description

The precise knowledge of the initial 26Al/27Al ratio [(26Al/27Al)0] is crucial if we are to use the very first solid objects formed in our Solar System, calcium-aluminum-rich inclusions (CAIs) as the "time zero" age-anchor and guide future work with other short-lived radio-chronometers in the early Solar System, as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation. New high-precision multi-collector inductively-coupled plasma mass...[Show more]

dc.contributor.authorJacobsen, Benjamin
dc.contributor.authorYin, Qing-zhu
dc.contributor.authorMoynier, Frederic
dc.contributor.authorAmelin, Yuri
dc.contributor.authorKrot, Alexander
dc.contributor.authorNagashima, Kazuhide
dc.contributor.authorHutcheon, Ian D
dc.contributor.authorPalme, Herbert
dc.date.accessioned2015-12-08T22:16:26Z
dc.identifier.issn0012-821X
dc.identifier.urihttp://hdl.handle.net/1885/30675
dc.description.abstractThe precise knowledge of the initial 26Al/27Al ratio [(26Al/27Al)0] is crucial if we are to use the very first solid objects formed in our Solar System, calcium-aluminum-rich inclusions (CAIs) as the "time zero" age-anchor and guide future work with other short-lived radio-chronometers in the early Solar System, as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation. New high-precision multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) measurements of 27Al/24Mg ratios and Mg-isotopic compositions of nine whole-rock CAIs (six mineralogically characterized fragments and three micro-drilled inclusions) from the CV carbonaceous chondrite, Allende yield a well-defined 26Al-26Mg fossil isochron with an (26Al/27Al)0 of (5.23 ± 0.13) × 10- 5. Internal mineral isochrons obtained for three of these CAIs (A44A, AJEF, and A43) are consistent with the whole-rock CAI isochron. The mineral isochron of AJEF with (26Al/27Al)0 = (4.96 ± 0.25) × 10- 5, anchored to our precisely determined absolute 207Pb-206Pb age of 4567.60 ± 0.36 Ma for the same mineral separates, reinstate the "canonical" (26Al/27Al)0 of 5 × 10- 5 for the early Solar System. The uncertainty in (26Al/27Al)0 corresponds to a maximum time span of ± 20 Ka (thousand years), suggesting that the Allende CAI formation events were culminated within this time span. Although all Allende CAIs studied experienced multistage formation history, including melting and evaporation in the solar nebula and post-crystallization alteration likely on the asteroidal parent body, the 26Al-26Mg and U-Pb-isotopic systematics of the mineral separates and bulk CAIs behaved largely as closed-system since their formation. Our data do not support the "supra-canonical" 26Al/27Al ratio of individual minerals or their mixtures in CV CAIs, suggesting that the supra-canonical 26Al/27Al ratio in the CV CAIs may have resulted from post-crystallization inter-mineral redistribution of Mg isotopes within an individual inclusion. This redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk CAI and bulk mineral data obtained by MC-ICP-MS. The radiogenic 208Pb*/206Pb* ratio obtained as a by-product from the Pb-Pb age dating is used to estimate time-integrated 232Th/238U ratio (κ value) of CAIs. Limited κ variations among the minerals within a single CAI, contrasted by much larger variations among the bulk CAIs, suggest Th/U fractionation occurred prior to crystallization of igneous CAIs. If interpreted as primordial heterogeneity, the κ value can be used to calculate the mean age of the interstellar dust from which the CAIs condensed.
dc.publisherElsevier
dc.sourceEarth and Planetary Science Letters
dc.subjectKeywords: Allende meteorite; carbonaceous chondrite; geochronology; isotopic composition; magnesium; radioactivity; solar system; uranium-lead dating 26Al/27Al ratio; Allende meteorite; Ca-Al rich inclusions; early Solar System chronology; short-lived radioactivity; U-Pb age
dc.title26 Al- 26 Mg and 207 Pb- 206 Pb systematics of Allende CAIs: Canonical solar initial 26 Al/ 27 Al ratio reinstated
dc.typeJournal article
local.description.notesImported from ARIES
local.identifier.citationvolume272
dc.date.issued2008
local.identifier.absfor020108 - Planetary Science (excl. Extraterrestrial Geology)
local.identifier.absfor040303 - Geochronology
local.identifier.absfor040203 - Isotope Geochemistry
local.identifier.ariespublicationu4047674xPUB76
local.type.statusPublished Version
local.contributor.affiliationJacobsen, Benjamin, University of California
local.contributor.affiliationYin, Qing-zhu, University of California
local.contributor.affiliationMoynier, Frederic, University of California
local.contributor.affiliationAmelin, Yuri, College of Physical and Mathematical Sciences, ANU
local.contributor.affiliationKrot, Alexander, University of Hawaii
local.contributor.affiliationNagashima, Kazuhide, University of Hawaii
local.contributor.affiliationHutcheon, Ian D, Lawrence Livermore National Laboratory
local.contributor.affiliationPalme, Herbert, University of Cologne
local.description.embargo2037-12-31
local.bibliographicCitation.issue1-2
local.bibliographicCitation.startpage353
local.bibliographicCitation.lastpage364
local.identifier.doi10.1016/j.epsl.2008.05.003
dc.date.updated2015-12-08T08:01:14Z
local.identifier.scopusID2-s2.0-47749156369
local.identifier.thomsonID000259119900034
CollectionsANU Research Publications

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