A light, chondritic xenolith in the Murchison (CM) chondrite – Formation by fluid-assisted percolation during metasomatism?

1Imene Kerraouch,2Samuel Ebert,2Markus Patzek,2Addi Bischoff,3Michael E.Zolensky,4Andreas Pack,6,7 Philippe Schmitt-Kopplin,1Djelloul Belhai,1Abderrahmane Bendaoud,7Loan Le
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2019.06.002]
1LGGIP, FSTGAT, Université des Sciences et de la Technologie Houari Boumediene, Alger, Algeria
2Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Wilhelm-Klemm Str. 10, D-48149 Münster, Germany
3ARES, NASA Johnson Space Center, Houston, TX, USA
4Universität Göttingen, Geowissenschaftliches Zentrum, Goldschmidtstr. 1, D-37077 Göttingen, Germany
5Helmholtz-Zentrum, München, German Research Center for Environmental Health, Analytical BioGeoChemistry, Ingolstädter Landstraße 1, D-85764 Neuherberg, Germany
6Chair of Analytical Food Chemistry, Technische Universität München, D-85354 Freising-Weihenstephan, Germany
7Jacobs ESCG, Houston, TX 77058, USA
Copyright Elsevier

The main mineralogical characteristics of a large light-colored clast within the Murchison CM breccia are discussed in detail including data on the mineralogy, bulk chemistry, organics, and oxygen isotopes. Petrographic study shows that the white clast consists of two areas with different granoblastic textures: (1) a coarse-grained (average grain size: ˜200 μm) and (2) a fine-grained lithology (average grain-size: ˜20 μm). The Fa-content of olivine in the clast is the same as Fa within olivine from Rumuruti (R) chondrites (Fa: ˜38 mol%); however, the concentrations of the elements Ni and Ca in olivine are significantly different. The fragment also contains Ca-rich pyroxene, ˜An30-38-plagioclase/maskelynite, Cr-rich spinel, several sulfide phases, a nepheline-normative glass, and traces of merrillite and metal. The occurrence of maskelynite and nepheline-normative amorphous phase in restricted areas of the well-recrystallized rock may indicate remarkable P-T-excursions during shock metamorphism. The O-isotope composition of the clast falls below the terrestrial fractionation line (TFL), lying in the field of CM chondrites and is significantly different from data for bulk R chondrites. The study of the soluble organic matter revealed a highly-oxidized carbon chemistry and organomagnesium compounds reflecting high temperature and pressure processes.

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