An updated catalogue of New Zealand’s mantle peridotite and serpentinite

Abstract

New Zealand has a remarkably large number of exhumed mantle occurrences for a small exposed landmass. Since the last regional syntheses of peridotite (1987) and serpentinite (1966), new locations have been discovered and abundant geochemical and isotopic data have been acquired. Mantle peridotite is known from nine massifs along the base of the Dun Mountain Ophiolite Belt (DMOB), xenoliths in volcanic fields in at least 75 localities, and as one 15 km-long orogenic body in Fiordland. In these occurrences, spinel peridotite is abundant, plagioclase peridotite is restricted to the DMOB, and garnet peridotite is absent. The xenoliths and orogenic peridotites represent exhumed lower portions of Phanerozoic continental lithosphere, whereas the ophiolites represent accreted oceanic lithosphere. Hydrated peridotite (serpentinite) is even more widespread, and extensively developed in three ophiolites (Dun Mountain, Northland and Pounamu). Serpentinite is also associated with some altered igneous ultramafic and mafic rocks. The recently acquired data have led to discoveries including the occurrence of Archean and Proterozoic mantle lithosphere under Zealandia, the presence of regional-scale fertile and refractory mantle lithosphere domains, isotopic similarities between metasomatised mantle and intraplate volcanic magmas, and characterisation of serpentinite during faulting.