Rare gases in a phlogopite nodule and a phlogopite-bearing peridotite in South African kimberlites

Abstract

Rare gas isotopes in a phlogopite nodule and a phlogopite-bearing peridotite nodule in South African kimberlites were studied to examine the state of rare gases in the deep interior of the kimberlite region. Within the experimental error of 1 ∼ 2%, rare gas isotopic compositions are atmospheric except for radiogenic 4He and 40Ar. No excess 129Xe was observed. In phlogopite, Ne is more depleted, whereas the heavier rare gases are more enriched than the atmospheric rare gases relative to 36Ar. Together with other data these results suggest that the state of rare gases in the upper mantle of the South African kimberlite region might have been changed from the typical primitive mantle by a process such as mixing of crustal materials.