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Oxygen and Al-Mg isotopic constraints on cooling rate and age of partial melting of an Allende Type B CAI, Golfball

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Title: Oxygen and Al-Mg isotopic constraints on cooling rate and age of partial melting of an Allende Type B CAI, Golfball
Authors: Kawasaki, Noriyuki Browse this author →KAKEN DB
Itoh, Shoichi Browse this author
Sakamoto, Naoya Browse this author
Simon, Steven B. Browse this author
Yamamoto, Daiki Browse this author
Yurimoto, Hisayoshi Browse this author
Issue Date: Jul-2021
Publisher: John Wiley & Sons
Journal Title: Meteoritics & Planetary Science
Volume: 56
Issue: 6
Start Page: 1224
End Page: 1239
Publisher DOI: 10.1111/maps.13701
Abstract: Coarse-grained, igneous Ca-Al-rich inclusions (CAIs) in CV chondrites formed through multiple melting events. We conducted in situ O-isotope analysis and Al-Mg systematics by secondary ion mass spectrometry of relict and overgrown minerals from a partial melting event in an Allende Type B CAI, Golfball. Golfball has a Type B CAI bulk composition and a unique structure: a fassaite-rich mantle enclosing a melilite-rich core. Many of the blocky melilite crystals in the core have irregularly shaped, Al-rich (angstrom k(5-15)) cores enclosed in strongly zoned (angstrom k(30-70)) overgrowths. Since the Al-rich melilite grains could not have formed from a melt of Golfball, they are interpreted as relict grains that survived later melting events. The O-isotopic compositions of the blocky melilite crystals plot along the carbonaceous chondrite anhydrous mineral line, ranging between Delta O-17 similar to -14 parts per thousand and -5 parts per thousand. The Al-rich relict melilite grains and their overgrowths exhibit the same O-isotopic compositions, while the O-isotopic compositions are varied spatially among melilites. We found that the O-isotopic compositions steeply change across several melilite crystals within few tens of micrometers, indicating the O-isotopic compositions of the melt could not have been homogenized during the partial melting in that scale. According to the time scale of O self-diffusivity in the melt, the cooling rate of the partial melting event is calculated to be >6 x 10(4) K h(-1). Al-Mg isotope data for core minerals plot on a straight line on an Al-Mg evolution diagram. A mineral isochron for Golfball gives initial Al-26/Al-27 of (4.42 +/- 0.20) x 10(-5) and initial delta Mg-26* of -0.035 +/- 0.050 parts per thousand. The chemical and O-isotopic compositions of melilite and those initial values imply that its precursor consisted of fluffy Type A and/or fine-grained CAIs. The partial melting event for Golfball may have occurred in very short order after the precursor formation.
Rights: This is the peer reviewed version of the following article: Meteoritics & planetary science, vol.56 no.6 pp.1224-1239, which has been published in final form at This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Use of Self-Archived Versions.
Type: article (author version)
Appears in Collections:理学院・理学研究院 (Graduate School of Science / Faculty of Science) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 川崎 教行

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