Physical and Chemical Properties of Matrix in Primitive Chondrites

Vaccaro, Epifanio (2017). Physical and Chemical Properties of Matrix in Primitive Chondrites. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.0000cc17

Abstract

The origin and formation of our Solar System is an open research question, which the scientific community is trying to address. In this work was specifically investigated the fine grained matrix which is a mixture of fine-grained materials composed largely of amorphous silicate and sub-micrometre crystals forsterite and enstatite. This is thought to be the remnants of the dust and gas of the protoplanetary disk that allows us to better understand chemical and physical properties of this precursor material. Four pristine primitive meteorites were selected: Acfer 094 (C2-ung.), ALHA77307 (CO3), MIL 07687 (C3-ung.) and QUE 99177 (CR2). The ability of a new generation of SEM-EDX detector was tested, in order to acquire high-resolution element maps of fine grained matrix. This allowed the calculation of abundances, and size distribution of discrete grains of different phases (silicate vs. opaque). Data acquired suggest that the four meteorites can be split into two groups, ALHA77307-MIL 07687 and QUE 99177 and Acfer 094, based on differences in relative abundances and sizes of discrete grains in their matrix. Micro X-ray diffraction was also used for mineralogical phase identification of the matrix constituents allowing the estimation of their modal mineralogy.

MIL 0768 and Acfer 094 were also investigated using Scanning Transmission X-ray Microscopy (STXM) which revealed predominantly oxidising conditions; some reducing conditions are also displayed by some grains, reflecting the mixed redox conditions of the solar nebula.

Measurements of O-isotopic composition of matrix regions were performed, and revealed similarities to values previously reported for IDPs (Starkey et al. 2013,2014 Nakashima et al., 2012, Aleon et al., 2009), rather than those of bulk meteorites (Clayton & Mayeda, 1999). I infer that the observed differences between these matrix components within the meteorite reflect the heterogeneity of the protoplanetary disk. Although these meteorites are pristine, parent body processes have also affected the small matrix grains.

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