DETERMINATION OF AN INTERNAL 87RB-87SR ISOCHRON FOR OLIVENZA CHONDRITE

RbSr isotopic determinations were made on five single chondrules, ranging from 4 to 27 milligrams, extracted from Olivenza, an olivine-hypersthene chondrite. Several density fractions with a particle size smaller than 37μ were separated and RbSr analyses made. These data form a well defined linear array on the SrRb evolution diagram and yield an age of 4.63 × 109 years and an initial 87Sr 86Sr = 0.6994. The typical strontium and rubidium blanks were 8 × 10-10 and 4 × 10-11 g, respectively. An acid wash experiment shows that preferential leaching takes place and that the resulting data from such a procedure are of doubtful reliability. Constructing an error envelope of the data points, a graphical representation of the initial 87Sr 86Sr versus the age is presented which demonstrates the constraints on these two anticorrelated parameters. This is a useful means of testing whether two data arrays may have the same age and ( 87Sr 86Sr)I. © 1969.