Rb-Sr age and strontium isotopic characterisation of the torlesse supergroup in canterbury, New Zealand, and implications for the status of the rakaia terrane

Abstract

Rb-Sr whole-rock isochron ages from 33 localities of low-grade metasediments of the Torlesse Supergroup in Canterbury date two episodes of burial metamorphism. Permian and Triassic metasediments were metamorphosed in latest Permian to Middle Triassic times (255–235 Ma), and in Late Triassic to Early Jurassic times (215–195 Ma), respectively. These data also confirm a consistent age (t), and initial 87Sr/86Sr ratio (i), relationship in both Permian and Triassic groups from Otago in the South Island to the Wellington region in the North Island. The (t)-(i) data of all Torlesse metasediments are more radiogenic than those in other Eastern Province terranes. In particular, Triassic Torlesse (t)-..