High-Mg adakites from Kadavu Island Group, Fiji, southwest Pacific: Evidence for the mantle origin of adakite parental melts

摘要

We report here the compositions of primitive high-Mg adakite lavas from the Kadavu Island Group, Fiji. Two distinctive high-Mg adakite compositions are present on Kadavu, and both are strongly enriched in Sr and La, with high Sr/Y (>120) and La/Yb (>30) values. The east Kadavu high-Mg adakite is relatively enriched in K2O and depleted in TiO2 and Nb. Our results from Kadavu suggest that there is an adakite magma series that is the result of complex open-system magmatic processes, including magma mixing between relatively low SiO2 mantle-derived melts of high-Mg adakite composition and high SiO2, low-Mg adakite magma. The results from Kadavu Island suggest that adakite magma suites worldwide are likely to include primitive high-Mg compositions, despite the lack of field evidence in many cases.