Determination of an internal ⁸⁷Rb-⁸⁷Sr isochron for the Olivenza chondrite

Abstract

Rb-Sr 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 Rb-Sr analyses made. These data form a well defined linear array on the Sr-Rb evolution diagram and yield an age of 4.63 × 10⁹ years and an initial ⁸⁷Sr⁸⁶Sr = 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 ⁸⁷Sr⁸⁶Sr 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 (⁸⁷Sr⁸⁶Sr)_I.

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