Abstract
Hf isotopic compositions of Archean rocks can provide valuable insights into early evolution of the mantle. We have been conducting isotopic ratio measurements of c.a. 3.5Ga basalts, which were collected from the Barberton Greenstone Belt in South Africa. While Hf isotopic data for Barberton komatiites have been reported, we have focused on pillow basalts having similar chemical compositions to modern basalts. Their Hf isotopic compositions can be used to compare modern and Archean mantles with similar features and to provide new constraints on komatiite petrogensis.
We have been developing new appropriate procedures for high MgO and FeO basalt samples, in which fluoride precipitates are not formed, and matrix elements are removed using AG1-X8 and Ln-Spec resins. This procedure yields 90% Hf recovery for Barberton samples. Further Hf isotopic analyses of Barberton samples, using the developed procedure, are in progress. In the presentation, we will report our new procedures and discuss early mantle evolution based on the Hf isotopic results obtained from Barberton basalts.
