Analysis of pathways for volatile-bearing mineral formation in carbonaceous chondrites using thermodynamic simulations

Abstract

Low temperature minerals in carbonaceous chondrites record volatile processes in the solar system. These processes could occur via liquid-solid or gas-solid reactions; however, few studies have considered gases. A Gibbs free energy minimization approach was used to investigate the formation of the Tagish Lake meteorite's low temperature matrix including gases and liquid water, with starting compositions of low O and high O determined from its bulk composition.

The high O model predicts phyllosilicate formation at <500 Degrees C, accounting for up to 24 mol% of solids and showing a similar compositional trend to observations of Tagish Lake's carbonate-rich lithology. Carbonates reached a maximum abundance of 50 mol% of solids at the lowest simulated temperature (0 Degrees C), being the most abundant group of minerals, excluding water. The low O model also formed phyllosilicates at <500 Degrees C, reaching up to ~18 mol% of solids, however carbonates were negligible. The low O phyllosilicate compositions more closely mirror the Tagish Lake's carbonate-poor lithology. The low O composition also predicts the coexistence olivine and abundant phyllosilicate for temperatures <150 Degrees C.

These models indicate the importance of O in carbonaceous chondrite alteration and confirm that high and low temperature minerals could coexist in carbonaceous chondrites in a system open to gas within the parent body. Also, this model provides a method of quantifying volatile loss due to heating on an asteroid. Show more