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.