A SURVEY OF RB-SR SYSTEMATICS OF EUCRITES

This paper surveys the experimental material on the Rb-Sr systematics of eucrites accumulated in the literature for the last two decades. Am ong the meteorites studied, those representatives have been chosen for which the absence of disturbances of isotope systems seems reliably f ixed (according to evidence from Rb-Sr, Sm-Nd, and U-Pb isotope data). These data have been subjected to joint statistical treatment. For or dinary eucrites the age has been estimated as T = 4.548 +/- 0.058 Ga, and initial Sr isotope ratio, I(ord) = 0.698925 +/- 14. For cumulate e ucrites, the initial Sr isotope ratio has been estimated as I(cum) = 0 .698872 +/- 14. The substantial difference in initial Sr isotope compo sition suggests that those two eucrite groups originate from distinct parent bodies. Joint treatment of the available Rb-Sr data for angrite s has been carried out for comparison, and the angrites initial Sr rat io has been estimated. On the basis of the estimates obtained formatio n intervals for the corresponding parent bodies have been calculated.