A study of the carbonaceous matter in carbonaceous chondrites for evaluating the degree of alteration/thermal metamorphism in meteorite parent bodies.

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1.Sulfur K-edge XAFS analysis of the chondrites shows the following results :(1)A typical XAFS spectrum of a CM chondrite shows the absorptions of inorganic sulfide, sulfate, and thiophenic (organic sulfur) absorptions.(2)The spectra of the CV (Allende) and CO (Ornans) chondrites lack in the sulfate and thiophenic absorptions, indicating the difference of parenrt bodies from the CM chondrites.(3)The spectra of unheated or weakly heated chondrites show relatively strong thiophenic absorption.(4)Based on the intensity of thiophenic absorption, the samples can be classified into the following groups : I Weak, corrssponds to strongly heated chondrites, II Comparable to the sulfidic absorption, corresponds to unheated or only weakly heated chondrites, III CV and CO chondrites.(5)Tagish Lake shows relatively strong thiophenic absorption, and relatively weak sulfate absorption is another characteristic of this sample.(6)The XAFS spectrum of the Muchison sample heated in laboratory lacks in the sulfate and thiophenic absorptions, suggesting such partial structure have been lost during heating.(7)Quantitative treatment of the XAFS spectra suggests that the unheated or weakly heated chondrites can be classified into two subgroups.2.Minerals in the Sayama and the CI-ike clast in the Tsukuba chondrites were determined by X-ray diffraction using synchrotron irradiation. The clast in Tsukuba chondrite have not been heated more than 500℃, and Oxygen isotope analysis of Sayama shows that it have experienced higher temperature (more than 120℃) than the other CM chondrites such as Murchison during its alteration.3.The laboratory simulation of aqueous alteration using Ningqiang shows that Q-gas have not been lost during alteration, but Ar-rich gas have been lost.