Physics

Geology

Meteorite

Isotope

Organic chemistry

Silicate minerals

Analytical Chemistry (journal)

Chondrite

Chondrule

Geochemistry

Mineralogy

Chemistry

Enstatite

Silicate

Parent body

Forsterite

Quantum mechanics

Isotopes of oxygen

Chromatography

Astrobiology

The Planetary Science Journal

Enstatite chondrites have been regarded as major building blocks of the Earth and other differentiated inner planetary bodies due to the similarity of Δ 17 O (deviation of the δ 17 O value from the terrestrial silicate fractionation line) and nucleosynthetic isotope anomalies. However, this hypothesis has been rebutted by the fact that the Earth and enstatite chondrites show distinct Si isotopic compositions. It has been debated whether the origin of this Si isotope difference is the result of nebular or planetary processes. Here we show that the δ 30 Si (deviation of 30 Si/ 28 Si relative to NBS 28 standard) and the Δ 17 O values of chondrules in unequilibrated enstatite chondrites are between −0.20‰ and −0.54‰ and −0.36‰ and +0.26‰, respectively. Furthermore, the chondrules with higher Δ 17 O values tend to have lower δ 30 Si. The data exhibit values consistent with most of the noncarbonaceous group differentiated planetary bodies. This consistency suggests that the Si and O isotopic compositions of enstatite chondrules record those of the major precursors that formed the differentiated planetary bodies in the inner solar system. Model calculations based on the results reveal that the Si and O isotope variations of the enstatite chondrite chondrules were generated by an interaction between the evaporation-driven SiO-rich gas and partially or fully melted forsterite-rich precursor chondrules. The Mg/Si of the evaporated dust-gas mixtures increased with increasing silicate/metal ratio in the evaporated dust, which may have increased the bulk Mg/Si and δ 30 Si value of the inner planetary bodies.

Silicon and Oxygen Isotope Evolution of the Inner Solar System