Universität zu Köln

Barosch, Jens ORCID: 0000-0002-0651-7348, Hezel, Dominik C., Ebel, Denton S. and Friend, Pia ORCID: 0000-0002-9042-3300 (2019). Mineralogically zoned chondrules in ordinary chondrites as evidence for open system chondrule behaviour. Geochim. Cosmochim. Acta, 249. S. 1 - 17. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 1872-9533

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Abstract

Chondrules are a major component of chondritic meteorites. Understanding their formation conditions provides fundamental insights about how the early solar system formed and evolved. We studied the textures of similar to 650 chondrules from all three groups (H, L, LL) of ordinary chondrites, in 2-dimensional (2D) sections through the meteorites. About 40% of the chondrules are mineralogically zoned. They consist of an olivine-rich core, which is surrounded by a low-Ca pyroxenerich rim. Chondrules sectioned through their low-Ca pyroxene rim do not appear as zoned chondrules, hence, considering such sectioning effects, their true fraction might be as high as similar to 50%. Mineralogical zonation is, therefore, a typical chondrule texture in basically all ordinary chondrites, and records a fundamental process during chondrule formation. Chondrules were open systems, and initially olivine-rich chondrules reacted with their surrounding gas to form low-Ca pyroxene rims. Zoned and unzoned chondrules have the same range of bulk compositions, thus ordinary chondrite chondrules were likely affected by two sequential episodes: in the first episode, gaseous SiO was added to all chondrules, thereby forming low-Ca pyroxene rims around all chondrules. In the second episode, only a portion of the chondrules were reheated, thereby remelting and homogenizing their initial pyroxene rims, but retaining their bulk compositions. It is therefore likely that all chondrules in ordinary chondrites were affected by gas-melt interactions during their formation. Open system exchange is consistent with previous studies of chondrule formation and can explain many chondrule textures and bulk chondrule compositional variations in single meteorites. Hence, the open system behaviour recorded in zoned chondrules provides a pivotal constraint on chondrule formation conditions. (C) 2019 Elsevier Ltd. All rights reserved.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Barosch, Jens UNSPECIFIED orcid.org/0000-0002-0651-7348 UNSPECIFIED Hezel, Dominik C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Ebel, Denton S. UNSPECIFIED UNSPECIFIED UNSPECIFIED Friend, Pia UNSPECIFIED orcid.org/0000-0002-9042-3300 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-153748
DOI:	10.1016/j.gca.2019.01.018
Journal or Publication Title:	Geochim. Cosmochim. Acta
Volume:	249
Page Range:	S. 1 - 17
Date:	2019
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	1872-9533
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Geosciences > Institute of Geology and Mineralog
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language OXYGEN-ISOTOPE SYSTEMATICS; CARBONACEOUS CHONDRITES; MAGNESIAN CHONDRULES; THERMAL HISTORIES; TRACE-ELEMENT; II CHONDRULES; ORIGIN; CONSTRAINTS; MATRIX; RESERVOIRS Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/15374