Occurrence of oxidized components in Qingzhen enstatite chondrite

Abstract

Clues to the early history of the Solar System can be acquired by studying the properties of highly unequilibrated chondrites. These chondrites are thought to preserve an almost unaltered record of nebular processes1–3. Here we show that the most unequilibrated enstatite chondrite4, Qingzhen, contains a population of enstatite grains which appear to have formed under more oxidizing nebular conditions than the bulk of the meteorite, which is highly reduced. These grains are black in transmitted light because of the presence of micrometre-sized inclusions of Ni-poor, Cr-rich metal and occur either isolated within the matrix or in chondrule interiors. Even though subsequent in situ reduction has led to the nucleation of metal, in most cases the FeO content of the enstatite grains still falls above the range found in the reduced portion of the meteorite. The textural occurrence of these grains argues against their having been introduced during collision of Qingzhen with an oxidized meteorite. Most likely, they originated in the same general nebular neighbourhood as the reduced bulk Qingzhen material and were subsequently transported into the reducing environment either before or during the process of chondrule formation. The discovery of this once-oxidized material in Qingzhen poses significant constraints on the existing models of formation of reduced matter in the Solar System.