study on the environmental and material evolution in the early system solar based on the chemical of composition of meteorites

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This year is the last year of the project. In this year, we have conducted the following research subjects ; (i) establishment of the analytical technique for four halogens in solid silicate materials and its application to meteorite samples, (ii) distribution of refractory siderophile elements in meteorites and its cosmochemical implications, (iii) distribution of rare earth elements (REEs), Th and U in meteorites and its cosmochemical implications, and (iv) development of analytical techniques applicable to meteorite samples. For the first subject, we established an analytical method for determining four halogens in a single sample weighing 50 to 100 mg and applied it to chondritic meteorite samples. We also investigated the distribution of Cl, Br and I in chondritic meteorites and observed that I is distributed in pyroxene and/or plagioclase to some extent, being different from Cl and Br. This observation seems to be very important in considering cosmochemical behavior of I, which has not been well described yet. For the second subject, we determined refractory siderophile elements in martian meteorites and observed that martian meteorites contain these elements at a level of 10^<-2> to 10^<-3> x Cl. This is understood in terms of an addition of siderophile elements as a last veneer after the formation of core. The third subject has just completed and the paper related with this subject will be prepared soon. In this subject, we determined REEs, Th and U in chondrules and observed that their abundances change in accordance with the activity of thermal metamorphism in the parent body.