Rarotonga Island as a mixing product of EM-1 and HIMU in the Cook-Austral volcanic chain, the South Pacific.

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We present radiogenic isotope (Os, Pb, Nd, Sr) and major and trace element data on lavas from Rarotonga Island, the Cock-Austral volcanic chain in the South Pacific, and examine the origin of the source of these lavas. Relationship between Ni, MgO and Os concentrations of the lavas indicates that Os contents in magma are controlled by fractionation of sulfide. The Os isotopic compositions of such samples lie in a small range between 0.1350 and 0.1381 with an average of 0.1369. This value is much lower than the value of approximately 0.15 widely accepted as the 187Os/188Os of EM-1. If in the case, the Os-Pb-Nd-Sr isotopic data of the Rarotonga lavas suggest that they are mixing products of EM-1 and HIMU.