| Matrix is an important component in the carbonaceous chondrites. Matrix has preserved the records of low-temperature process of early solar nebula because it escapes the high-temperature events happened in the early solar nebula. The mineralogy and chemical composition of matrix reflect history of the early solar nebula formation and evolution, especially its aqueous alteration processe is closely related with evolution of the early solar nebula with low temperature. Therefore matrix is the witness to formation and evolvement of the early solar nebula. The characteristics of petrology, mineralogy and chemical composition of matrix in the six Antarctic unequilibrated carbonaceous chondrites have been investigated in detail by optical microscope, scanning electron microscopy (SEM) and electron microprobe analysis (EMPA).Then the conclusions can be drawn as follows:1. That the matrix structure and mineral assemblages of three types carbonaceous chondrites (CM, CV and CR) of the Grove Mountains is investigated. There are significant differences for different types of carbonaceous chondrites matrix in particle size, mineral assemblages, and aqueous alteration.2. Detailed petrological and chemical features of matrix indicate that matrix can be divided into three types of distinct occurrences: (1) interchondrules matrix, (2) fine-grained rims, (3) dark inclusions.3. Based on the structure and the mineralogy of the matrix, the types of three Grove Mountains carbonaceous chondrite are modified: (1) GRV021579 is reclassified into CM2, (2) GRV022459 is further subgrouped as CVR3, and (3) GRV020005 is reclassified into CM1.4. The loose structure and large amount of amorphous material show that the matrix is formed from the nebula condensation. According to the internal structure of matrix as well as relationship with the other components of the chondrite, the formation process of the matrix was inferred as:Formation of dark inclusions→Condensation of fine-grained rims→Aggregation of the interchondrules matrix, and then this materials mix with the other high-temperature components to form the meteorites parent body. Then the parent body undergoes a general aqueous alteration.5. Aqueous alteration characteristics in carbonaceous chondrites show that the aqueous alteration of carbonaceous chondrites is maybe multi-staged. The difference between the chondrule and the matrix indicates that aqueous alteration in the chondrule may be occurred in the nebula, but the aqueous alteration occurring widely in the matrix may be occurred in the parent process. 6. The significant differences of structure and composition in the different carbonaceous chondrite matrix and even the heterogeneous chemical composition in a single meteorite matrix suggest that the early solar nebula is highly heterogeneous in composition. |
