Metamorphism in chondrites

Abstract

The concept of chondrites as metamorphic rocks is examined. Mineralogies of four chondrites whose textures indicate different degrees of thermal recrystallization are presented. It appears that relatively unmetamorphosed or “primary” chondritic material consisted of reduced chondrules (metallic iron, magnesian silicates) in an oxidized matrix (containing ultrafinegrained magnetite, no metallic iron). It is suggested that chondrules condensed as liquid droplets from cooling solar gases during the formation of the sun, later accreting into planets and asteroids. Such a process could account for the peculiar oxidation-reduction state of relatively unmetamorphosed chondrites, such as Renazzo.