The chemical relationship between chondrules and matrix and the chondrule matrix complementarity

摘要

Chondrules and matrix are the two major components of carbonaceous chondrites (CC). The Mg/Si ratios of chondrules and matrices in CV, CR, CO and CM chondrites are complementary: chondrules have super Cl chondritic and matrices sub Cl chondritic Mg/Si ratios. Bulk samples of CC have always CI chondritic Mg/Si ratios, indicating that chondrules and matrix are chemically connected. Such a chemical relationship places important constraints on the chondrule formation process and the chemical evolution of the protoplanetary disk. The chondrule matrix complementarity excludes separate origins and later mixing of chondrules and matrix. Redistribution of Fe and Mg between chondrules and matrix or leaching of Si from chondrule mesostasis into the matrix on the parent body can be excluded. Both, chondrules and matrix must have formed from the same chemical reservoir. The Mg/Si complementarity was probably established in the nebula before parent body accretion by the extraction of a Mg-rich component from a Cl chondritic reservoir. This component then served as precursor for chondrules, leaving behind Mg-depleted material, the parent material of matrix. This interpretation excludes all chondrule forming processes that involve a separate origin for chondrules and matrix, such as, for example, the X-wind model. The existence of this complementarity in CV, CR, CO and CM chondrites also suggests that chondrules and matrix are formed by similar processes.