Chondrules in enstatite chondrites

TL;DR

This paper reviews the mineralogical features of silicate chondrules and metal-sulfide nodules in enstatite chondrites, suggesting their formation involved highly reduced conditions and complex processes possibly occurring inside the snow line.

Contribution

It provides a comprehensive analysis of enstatite chondrite chondrules, proposing new insights into their formation environment and processes, including sulfidization and impact origins.

Findings

Chondrules show unique mineral assemblages indicating reduced conditions.

Sulfidization likely occurred in an O-poor, S-rich environment.

Metal-sulfide nodules may originate from impact processes or silicate chondrules.

Abstract

We review silicate chondrules and metal-sulfide nodules in unequilibrated enstatite chondrites (EH3 and EL3). Their unique mineralogical assemblage, with a wide diversity of opaque phases, nitrides, nearly FeO-free enstatite etc. testify to exceptionally reduced conditions. While those have long been ascribed to a condensation sequence at supersolar C/O ratios, with the oldhamite-rich nodules among the earliest condensates, evidence for relatively oxidized local precursors suggests that their peculiarities may have been acquired during the chondrule-forming process itself. Silicate phases may have been then sulfidized in an O-poor and S-rich environment; metal-sulfide nodules in EH3 chondrites could have originated in the silicate chondrules whereas those in EL3 may be impact products. The astrophysical setting (nebular or planetary) where such conditions were achieved, whether by depletion in water or enrichment in dry organics-silicate mixtures, is uncertain, but was most likely sited inside the snow line, consistent with the Earth-like oxygen isotopic signature of most EC silicates, with little data constraining its epoch yet.