Brook street and Murihiku terranes of New Zealand in the context of a mobile South Pacific Gondwana margin

Abstract

Data from geochemistry, isotope studies and paleomagnetism suggest that both the Permian arc-dominated Brook Street terrane and Triassic-Jurassic Murihiku forearc basin terrane are unrelated to each other and that both are allochthonous with respect to the Gondwana margin. The Murihiku terrane lies farther from the Gondwana margin but its fauna and flora have strong Gondwana affinities and closely resemble those of autochthonous epi-Gondwana basins in Australia and Argentina. All terranes within New Zealand are elongate parallel to the Gondwana margin but very few can be clearly identified in the Australian and Antarctic continental crust that abuts New Zealand in Cretaceous Gondwana reconstructions. Similarly, some Australia terranes do not appear to continue into New Zealand or Antarctica. This suggests that breakup was influenced significantly by old terrane boundaries and also that there was considerable terrane mobility in the active Gondwana margin before the Cretaceous. A systematic comparison of arc chemistry, geochronology, biota, and paleomagnetism is desirable to constrain the development of the South Pacific margin between Australia and South America in the Mesozoic.