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High time resolution by use of the ^(26)Al chronometer in the multistage formation of a CAI

Hsu, Weibiao and Wasserburg, G. J. and Huss, Gary R. (2000) High time resolution by use of the ^(26)Al chronometer in the multistage formation of a CAI. Earth and Planetary Science Letters, 182 (1). pp. 15-29. ISSN 0012-821X. doi:10.1016/S0012-821X(00)00233-8.

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The Allende calcium-rich inclusion (CAI) 5241 has been found to contain distinct initial ^(26)Al/^(27)Al in the three consecutive igneous zones that have been identified by extensive petrogenetic studies to have formed in three distinct crystallization events. The zones in order of sequence of formation from the petrologic observations are: (1) spinel-free islands (SFI) included in (2) a pyroxene–spinel-rich core (SRC) which in turn is included in (3) a melilite mantle (MM). The initial (^(26)Al/^(27)Al) values of these zones are respectively (4.6–5.0)×10^(−5), 4.3×10^(−5), and 3.3×10^(−5). It is argued that these distinct (^(26)Al/^(27)Al)0 values are not the result of metamorphism but reflect the relative times of formation by crystallization from melts. Relative to the canonical value of (^(26)Al/^(27)Al)0=5×10^(−5), we find the following chronology: t_(SFI)≈0, t_(SRC)≈10^5 yr and t_(MM)≈4×10^5 yr. The three-layer CAI is inferred to have sampled a reservoir with an initial uniform ^(26)Al/^(27)Al ratio that decreased in value due to radioactive decay. From these observations we conclude that we have resolved time differences of a few hundred thousand years at the very early stages of formation of the solar system. The SFI, SRC, and MM zones reflect sequential addition of molten CAI material which crystallized rapidly without seriously metamorphosing the previously formed material. These additions took place over a time of about 400 000 years. We believe that these sequential events are not compatible with condensation in a hot region of the solar nebula. It is proposed that a scenario involving stages of protoplanetary accretion and of melt generation in protoplanetary sites heated by ^(26)Al might provide a possible source for CAIs and chondrules.

Item Type:Article
Related URLs:
URLURL TypeDescription
Wasserburg, G. J.0000-0002-7957-8029
Huss, Gary R.0000-0003-4281-7839
Additional Information:© 2000 Elsevier Science B.V. Received 29 May 2000; received in revised form 17 July 2000; accepted 24 July 2000. This paper is dedicated to Brian Mason of the U.S. National Museum who graciously provided us this material and who has, as always, been a guiding, friendly beacon in many things meteoritic. We have pro¢ted greatly from insightful and positive reviews. The anonymous reviewer has improved the introduction, A. El Goresy has directed us to major petrogenetic issues and Ernst Zinner has given a meticulous and penetrating critique that was of great use in improving this report. This work was supported by NASA NAG5-4083 (G.J.W.), NAG5-8158 (G.R.H.), and by the MacArthur Endowment Fund. Division Contribution Number: 8724(1055).[AH]
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MacArthur Endowment FundUNSPECIFIED
Subject Keywords:calcium-aluminium inclusions; Al-26; chondrules; solar system
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Caltech Division of Geological and Planetary Sciences8724
Lunatic Asylum Lab1055
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Record Number:CaltechAUTHORS:20131115-105039012
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Official Citation:Weibiao Hsu, G.J. Wasserburg, Gary R. Huss, High time resolution by use of the 26Al chronometer in the multistage formation of a CAI, Earth and Planetary Science Letters, Volume 182, Issue 1, 15 October 2000, Pages 15-29, ISSN 0012-821X, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:42494
Deposited By: Ruth Sustaita
Deposited On:15 Nov 2013 19:23
Last Modified:10 Nov 2021 16:24

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