A re-assessment of moderately volatile elements in the non-matrix component of carbonaceous chondrites

13/03/2026 23:00 · by karmaka · in carbonaceous chondrite, chondrite components, chondrule, chondrule formation, matrix

Zhongtian Zhang, Damanveer S. Grewal

Icarus
Available online 13 March 2026, 117049

“Highlights

Updated matrix fractions lead to revised MVE abundances in the non-matrix component.
Non-matrix (chondrule) MVE abundances are lower than previously estimated.
Chondrule-matrix MVE isotopic fractionations are larger than previously estimated.
MVE elemental and isotopic signatures may develop during chondrule formation.”

“All carbonaceous chondrites are variably depleted in moderately volatile elements (MVEs) relative to CI chondrites, which closely match the bulk composition of the Solar System. This MVE depletion is thought to reflect mixing between a CI-like matrix and an MVE-depleted non-matrix component. Since the non-matrix component is primarily composed of chondrules, constraining the extent of MVE depletion in the non-matrix component is critical for understanding chondrule formation. Two approaches have been applied previously to estimate MVE abundances in the non-matrix component, yielding differing predictions. The first relies solely on chondrite compositions, while the second combines chondrite compositions with matrix mass fractions. The latter, which has gained wide acceptance, predicts that the abundances of MVEs with 50% nebular condensation temperatures below ~750K (the so-called “plateau” MVEs) in the non-matrix component are ~ 0.13xCI. These estimated abundances have been further used to constrain the mass-dependent isotopic compositions of MVEs in the non-matrix (or chondrule) component. However, the matrix mass fractions employed in these fits have been challenged by detailed analyses of several carbonaceous chondrite groups. In this study, we use the revised matrix mass fractions to re-assess the MVE contents of the non-matrix component in carbonaceous chondrites. The results suggest that many MVEs occur in the non-matrix component at levels below ~ 0.13xCI abundances, consistent with the first approach that does not use matrix mass fractions as input data. Based on our new results, the mass-dependent isotopic fractionations for “plateau” MVEs such as Zn and Te between matrix and non-matrix components are inferred to be larger than previously estimated. We discuss the possible origins of the elemental and isotopic compositions of the non-matrix component and suggest that they can be explained by chondrule formation alone, without invoking inheritance from chondrule precursors.”