Abstract

Trace element contents of mineral separates from the eastern Rhum layered series, Inner Hebrides, have been determined using instrumental and radiochemical neutron activation analysis. The data are consistent with the hypothesis of frequent magma pulses of constant composition into a magma chamber.The high concentrations found for "incompatible" elements in plagioclase from the lower units can be correlated with the amount of trapped liquid in the original cumulates.The average iridium content of plagioclase, clinopyroxene, and olivine is 0.06 ppb, 0.075 ppb, and 0.35 ppb, respectively, but pure olivine probably contains about 0.07 ppb. The iridium content of the Rhum magma is thought to be two orders of magnitude lower than that of the Bushveld magma.

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