Abstract
The aqueously altered CM carbonaceous chondrite meteorites can be used to investigate the nature and transport of volatiles in the early solar system. We present the preliminary results of an effort to collect 2D infrared (IR) spectral maps from the matrix and fine-grained rims (FGRs) of material that surround chondrules and inclusions in the Murchison CM2 meteorite using synchrotron IR micro-spectroscopy. The main features in mid-IR spectra of the matrix and FGRs occur at ∼3500 cm−1 and ∼1000 cm−1 and are attributed to OH/H2O and SiO bonds in phyllosilicates and anhydrous silicates. Minor features in the spectra are attributed to organic species (3000–2800 cm−1), CO2 (2400–2000 cm−1), and carbonates (1500–1380 cm−1). In both the matrix and FGRs we observe correlations between the OH/H2O and phyllosilicate/silicate features confirming that phyllosilicates dominate the mineralogy. This is consistent with previous studies showing that Murchison contains ∼70 vol% phyllosilicates following aqueous alteration on an asteroid parent body. The presence of anhydrous silicates in the matrix indicates that the alteration was heterogeneous at the micron-scale and that the reactions did not reach completion. We highlight a possible correlation between the phyllosilicates and organic species in the matrix, supporting the hypothesis that phyllosilicates may have played an important role in the formation and preservation of simple organic molecules and compounds. In the FGRs variations in the distribution of the phyllosilicate minerals cronstedtite and Mg-serpentine/saponite likely reflect differences in the local geochemical conditions during aqueous alteration on the asteroid.
Highlights
Primitive meteorites provide a glimpse into the processes and events that have shaped our solar system over the last ∼4.5 billion years
∼3500 cm−1 and ∼1000 cm−1 and are attributed to eOH/H2O and SieO bonds, respectively. This is consistent with the mineralogy of Murchison, which is known to contain both hydrous Fe- and Mg-rich phyllosilicates and anhydrous silicates, and is in good agreement with previous IR studies of CM chondrites [3,4,5,6]
The aqueously altered CM carbonaceous chondrite meteorites are physical samples of water-rich asteroids that offer a direct probe into the characteristics of volatile reservoirs in the solar system
Summary
Primitive meteorites provide a glimpse into the processes and events that have shaped our solar system over the last ∼4.5 billion years. The CM (“Mighei-type”) carbonaceous chondrite meteorites consist of calcium-aluminium-rich inclusions (CAIs), chondrules and silicate fragments set within a matrix (> ∼50 vol%) of phyllosilicates, oxides, sulphides and carbonates. They contain ∼10 wt% extra-terrestrial H2O and are interpreted as the products of low temperature (< 100 °C) aqueous alteration after ices melted on a water-rich asteroid parent body [1]. The CM chondrites experienced varying degrees of aqueous alteration and many are regolith breccias, resulting in heterogeneous textures It is spatially resolved micro- and nano- techniques that are likely to provide the most comprehensive picture of the aqueous reactions on asteroids
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