A NONDESTRUCTIVE ANALYTICAL METHOD FOR STONE METEORITES - AND A CONTROVERSIAL DISCREPANCY

A method is described for whole rock analyses of major elements in sto ne meteorites using the electron microprobe and requiring only powderi ng of the sample, most of which can be retrieved after analysis for ad ditional analytical studies, such as instrument neutron activation ana lysis (INAA), radiochemical neutron activation analysis (RNAA) and O-i sotopic analysis. Whole individual chondrules of less than or equal to 1 mg can be analyzed. The method is especially attractive for meteori tes in short supply or of great rarity. A total of 398 meteorites were analyzed by this method. The results compare favorably with wet chemi cal analyses. A study was made of seventeen ordinary chondrites to com pare their whole rock (metal free) compositions with the averaged comp ositions of eleven to thirty-eight of their respective individual chon drules (a total of 374 chondrules). The oxide ratio Al2O3/CaO is gener ally lower in chondrules than in their respective chondrites, the disp arity being larger for petrographic grade 5 than for grade 3. Ordinary chondrites are not simply the sum of their respective chondrules. Fur thermore, correlations between CaO, Al2O3 and TiO2 are strong for chon drules in unequilibrated chondrites and nonexistent in equilibrated ch ondrites. Also H, L and LL chondrite groups have similar bulk composit ions within their respective groups, in spite of the different proport ions of chondrules, kinds of chondrules, chondrule debris, and matrix. All this brings into question the metamorphic classification in which high petrographic grades are the metamorphosed equivalents of low pet rographic grades.