Abundance, Major Element Composition and Size of Components and Matrix in CV, CO and Acfer 094 Chondrites

TL;DR

This study introduces new analytical techniques to quantify the composition and abundance of inclusions and matrix in CV, CO, and Acfer 094 chondrites, revealing compositional trends and complementarity that inform astrophysical formation models.

Contribution

The paper presents innovative methods for pixel-by-pixel major element analysis of chondrite inclusions and matrix, enhancing understanding of their compositional relationships and formation processes.

Findings

Inclusions show wide compositional variation but sum to near-solar ratios.

Matrix and inclusions' Mg/Si ratios approach solar with increasing petrologic grade.

Oxidized CV chondrites have higher porosity and matrix-inclusion ratios, linked to aqueous alteration.

Abstract

The relative abundances and chemical compositions of the macroscopic components or "inclusions" (chondrules and refractory inclusions) and fine-grained mineral matrix in chondritic meteorites provide constraints on astrophysical theories of inclusion formation and chondrite accretion. We present new techniques for analysis of low count per pixel Si, Mg, Ca, Al, Ti and Fe x-ray intensity maps of rock sections, and apply them to large areas of CO and CV chondrites, and the ungrouped Acfer 094 chondrite. For many thousands of manually segmented and type-identified inclusions, we are able to assess, pixel-by-pixel, the major element content of each inclusion. We quantify the total fraction of those elements accounted for by various types of inclusion and matrix. Among CO chondrites, both matrix and inclusion Mg to Si ratios approach the solar (and bulk CO) ratio with increasing petrologic grade, but Si remains enriched in inclusions relative to matrix. The oxidized CV chondrites with higher matrix-inclusion ratios exhibit more severe aqueous alteration (oxidation), and their excess matrix accounts for their higher porosity relative to reduced CV chondrites. Porosity could accommodate an original ice component of matrix as the direct cause of local alteration of oxidized CV chondrites. We confirm that major element abundances among inclusions differ greatly, across a wide range of CO and CV chondrites. These abundances in all cases add up to near-chondritic (solar) bulk abundance ratios in these chondrites, despite wide variations in matrix-inclusion ratios and inclusion sizes: chondrite components are complementary. This "complementarity" provides a robust meteoritic constraint for astrophysical disk models.