Crustal evolution of New Zealand: Evidence from age distributions of detrital zircons in Western Province paragneisses and Torlesse greywacke

Abstract

Individual zircon grains from three Western Province paragneisses and a sample of Torlesse greywacke have been dated by ion microprobe mass spectrometry. The paragneisses have zircon age distributions that indicate maximum ages of deposition of Ordovician to Devonian with Cretaceous metamorphism. Archean zircons as old as 3400 Ma have been identifiedand distinct components are present at 1700 Ma, 1050 Maand 500–600 Ma. These characteristics are identical to zircon age distributions in Ordovician sediments from eastern Australia suggesting a common provenance. The Torlesse greywacke has a Permian-Triassic sedimentary age and the zircons are predominantly 260 Ma old. Rounded detrital zircons in the greywacke range in age from 340 to 1240 Ma with peaks in the age distribution at 500–600 Ma and 1100 Ma, similar to that seen from the Western Province paragneisses. However, this does not necessarily require a western origin for Torlesse sediments. Further work is required to establish whether the zircon age distribution in the Western Province paragneisses and eastern Australian sediments is a regional characteristic of the Pacific margin of Gondwana.