Age/isotopic characterisation of the waipapa group in Northland and Auckland, New Zealand, and implications for the status of the waipapa terrane

Abstract

Rb-Sr ages of low-grade metasediments of the Waipapa Group (probable Permian-Jurassic) of Northland and Auckland range from Late Triassic (c. 209–217 Ma) to Middle Jurassic (c. 164–174 Ma), reflecting deformation and metamorphism during the Rangitata Orogeny. K-Ar ages indicate Middle Jurassic (c. 165–175 Ma) uplift and cooling of the western Omahuta-Puketi Forest block, and later, Middle-Late Jurassic (c. 150–160 Ma) cooling of the Helena Bay to Hunua Ranges eastern coastal block. In the intervening Western Bay of Islands block, there is evidence of local Early Cretaceous (c. 135 Ma) metamorphism. Rb-Sr whole-rock isochron age (t) and initial 87Sr/86Sr ratio (i) data support the assignment ..