Abstract
Rb-Sr analyses of silicates from the Colomera iron meteorite show a wide range in Rb/Sr and give 87Sr 86Sr values ranging from 0.699 to 8.45. These analyses define a precise linear array on the Rb-Sr evolution diagram yielding an age of 4.61 ± 0.04 × 10 9 yr. A highprecision analysis of a whitlockite separate having very low Rb/Sr yields an initial ( 87Sr 86Sr ) I = 0.69940 ± 0.00004 . An upper limit of 48 ± 7 million years can be set for the time interval between dispersion of the silicate in the metal phase and final Sr isotopic equilibration, if we assume that Colomera silicate formed from a parent material which had the same initial 87Sr 86Sr as Ca-rich achondrites. The data are consistent with a simple evolutionary history in which Colomera differentiated from a parent material of chondritie Rb Sr ratio at a time 39 million years after the parent material had the initial 87Sr 86Sr of Ca-rich achondrites and 35 million years before the final Sr equilibration in the Guareña chondrite.
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