Universität zu Köln

Braukmueller, Ninja, Wombacher, Frank ORCID: 0000-0002-0755-8918, Hezel, Dominik C., Escoube, Raphaelle and Muenker, Carsten (2018). The chemical composition of carbonaceous chondrites: Implications for volatile element depletion, complementarity and alteration. Geochim. Cosmochim. Acta, 239. S. 17 - 49. OXFORD: PERGAMON-ELSEVIER SCIENCE LTD. ISSN 1872-9533

Full text not available from this repository.

Abstract

In Earth and planetary sciences, the chemical composition of chondritic meteorites provides an essential reference to constrain the composition and differentiation history of planetary reservoirs. Yet, for many trace elements, and in particular for volatile trace elements the composition of chondrites is not well constrained. Here we present new compositional data for carbonaceous chondrites with an emphasis on the origin of the volatile element depletion pattern. Our database includes 25 carbonaceous chondrites from 6 different groups (CI, CM, CR, CV, CO, CK), two ungrouped carbonaceous chondrites and Murchison powder samples heated up to 1000 degrees C in O-2 or Ar gas streams, respectively. A total of 51 major and trace elements were analyzed by sector field inductively coupled plasma mass spectrometry (SF-ICP-MS), using chondrite-matched calibration solutions. Our results confirm that parent body alteration and terrestrial weathering only have minor effects on the bulk chondrite compositions. Thermal metamorphism can lead to the loss of some volatile elements, as best observed in the heating experiments and two thermally overprinted chondrites Y-980115 (CI) and EET 96026 (CV4/5 or CK4/5). The effects of aqueous alteration and terrestrial weathering on the Antarctic samples are difficult to discriminate. Both processes may redistribute fluid mobile elements such as K, Na, Rb, U and the light rare earth elements (LREE) within the meteorite. In hot desert finds, the typical weathering effects are enrichments of Sr, Ba and U and a depletion of S. In general, moderately volatile elements with 50% condensation temperatures (T-c) ranging from 1250 K to 800 K show an increasing depletion, whereas 11 moderately volatile elements with 50% T-c between 800 K and 500 K are unfractionated from each other in most samples. Their extent of depletion is characteristic for the different chondrite groups. Because of this welldefined hockey stick pattern, we propose to divide the moderately volatile elements into two subgroups, the 'slope volatile elements' and the unfractionated 'plateau volatile elements' with lower T-c . Notably, the abundances of plateau volatile elements exhibit a co-variation with the matrix abundances of the respective host meteorites. Carbonaceous chondrite matrices are likely mixes of: (i) CI-like material and (ii) chondrule-related matrix. Chondrule-related matrix is expected to be depleted in volatile elements relative to CI and likely formed contemporaneously with chondrules, leading to chondrule-matrix complementarity. The addition of CI-like material only changed the absolute elemental concentrations of bulk matrix and bulk chondrite, while refractory and main component element ratios such as Mg/Si remain unaffected. Such a model can also account for the co-existence of low temperature CI-like material and high temperature chondrule and chondrule-related matrix. However, elevated volatile element abundances observed in chondrules still provide a challenge for the model as proposed here. (C) 2018 The Author(s). Published by Elsevier Ltd.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Braukmueller, Ninja UNSPECIFIED UNSPECIFIED UNSPECIFIED Wombacher, Frank UNSPECIFIED orcid.org/0000-0002-0755-8918 UNSPECIFIED Hezel, Dominik C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Escoube, Raphaelle UNSPECIFIED UNSPECIFIED UNSPECIFIED Muenker, Carsten UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-169316
DOI:	10.1016/j.gca.2018.07.023
Journal or Publication Title:	Geochim. Cosmochim. Acta
Volume:	239
Page Range:	S. 17 - 49
Date:	2018
Publisher:	PERGAMON-ELSEVIER SCIENCE LTD
Place of Publication:	OXFORD
ISSN:	1872-9533
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language EARLY SOLAR-SYSTEM; PRIMITIVE METEORITES; TRACE-ELEMENTS; THERMAL METAMORPHISM; IRON-METEORITES; TAGISH LAKE; ISOTOPIC CONSTRAINTS; CHONDRULE FORMATION; AQUEOUS ALTERATION; MODAL MINERALOGY Multiple languages Geochemistry & Geophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/16931