Terrane characterisation and timing of metamorphism in the Otago Schist, New Zealand, using Rb-Sr and K-Ar geochronology

A Rb-Sr whole-rock study of the Otago Schist, southern South Island, New Zealand, parallels earlier K-Ar dating and indicates a Jurassic age for schist metamorphism and initiation of uplift, and a Cretaceous age for completion of uplift and final closure of the isotopic systems. Initial (87)Sr/(86)Sr ratios provide a useful fingerprinting method to enable determination of the terrane affinity (Torlesse or Caples) of the schist. Torlesse rocks range in initial (87)Sr/(86)Sr from 0.7065 to 0.7098, consistent with a cratonic/felsic-volcanic provenance. Caples rocks range in initial (87)Sr/(86)Sr from 0.7035 to 0.7055, consistent with an intra-oceanic volcanic arc provenance. The data provide strong support for geochemical correlation of the Caples Terrane with Pelorus and Waipapa Groups in the northern part of New Zealand.