The Lord Howe Volcanic Complex, Australia: its geochemistry and origins

Abstract

ABSTRACT The Lord Howe Volcanic Complex (LHVC) is part of a seamount chain associated with the detached continental crust of Zealandia. We present petrographic and geochemical data for the LHVC, including the first reported data for Balls Pyramid and the first trace element data for Lord Howe Island, clarifying the tectonic affiliation and general mantle source characteristics. Classification and discrimination diagrams based on concentrations and ratios of immobile elements, such as rare earth and high field strength elements, Th, Ti, Y, and Mg, show the LHVC comprises transitional to alkali basalts and at least two, and probably three, shield building complexes, consistent with an intraplate tectonic setting. Primitive-mantle normalised trace element patterns, variation in Dy/Yb for a restricted range of Dy/Dy*, Zr/Yb > 90, and variations in Zr/Hf and P2O5/TiO2 through the eruptive sequences indicate the mantle source may be a laterally heterogeneous enriched garnet peridotite that has undergone varying degrees of partial melting and carbonatitic metasomatism, both within the LHVC and along the Lord Howe Seamount Chain. The LHVC is thus an ideal natural laboratory for probing the probability of small intraplate volcanic fields originating via mantle plumes or from previously subducted slabs stagnating at the mantle transition zone.