The confirmation of a new type of chondrites and their cosmochemical significance

Abstract

The data available show that some Antarctic carbonaceous chondrites are similar to Cl meteorites. They contain a lot of phyllosilicate aggregates and the oxygen isotopic composition of the whole-rock samples is approximate to that of Cl chondrites, so they are named after quasi-Cl (Q-Cl) chondrites. Unlike Cl meteorites, the Q-Cl chondrites possess chondrule structure, and the compositions of high-temperature condensates (chondrule fragments, mineral grains or aggregates) show that the oxygen fugacity varied within a wide range in the surroundings where they were formed, similar to the variation range from E-, H-, L-, LL-to C-group chondrites. It is inferred that the Q-Cl chondrites could be formed at the edges far from the equator in the whole asteroid region of the solar nebular disk, where the nebula was lower in density and the condensates were lower in accretion velocity, so that the hydration of chondrules and matrix occurred during the late stage of nebular condensation. The discovery of the Q-Cl chondrites and the fact that the earth and other terrestrial planets contain water indicate that at the edges far from the equator in the terrestrial region of the solar nebular disk, a large amount of water was incorporated into the lattice of minerals in the condensates as a result of hydration during nebular condensation, and then found its way into the interior parts of the Earth and other terrestrial planets due to accretion.