RUBIDIUM-STRONTIUM CORRELATION STUDY OF MOLDAVITES AND RIES CRATER MATERIAL

The Sr87 Sr86 values of nine moldavites are essentially constant at 0.722 ± 0.001, although the Rb Sr ratios vary from 0.77 to 1.2. This very uniform Sr isotopic composition indicates either that the parent material was (a) quite homogeneous or homogenized during the fusion event, or (b) a heterogeneous mixture of two or more phases with different Rb Sr, perhaps created during the fusion event, in which the isotopic composition of Sr was dominated by that of a Sr-rich component. Possibilities (a), unlike (b), require that Rb and Sr have been differentially fractionated less than 108 years ago. Crystalline rock fragments, glasses, and suevite from the Ries crater have insufficient spread in Rb/Sr and show too much scatter to yield an isochron. The Ries materials have distinctly lower Rb/Sr and Sr87 Sr86 values than the moldavites. In contrast to the Ivory Coast tektite-Bosumtwi crater relationship, no definite isochronal correlation or chemical similarity was detected between the moldavites and Ries crater rocks, suevite and glasses. Thus this work supports previous suggestions that the moldavites are not simply melted equivalents of these Ries materials. © 1969.