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

Geochronologic constraints of the uplift and metamorphism along the Alpine Fault, South Island, New Zealand

“…The pegmatites are of granitic composition, containing quartz, biotite, muscovite, potassium feldspar, plagioclase, tourmaline, with minor amounts of zircon and monazite (Wellman 1947;Wallace 1974). Petrological study of these pegmatites (Wallace 1974) suggests that they formed as partial melts of the Alpine Schist, an interpretation supported by similarity between the initial 87 Sr/ 86 Sr of the pegmatites (0.7053; calculated at 68 Ma from the data of Aronson (1965)) and the Otago Schist (0.7061; calculated from Aronson (1965) or 0.7065 to 0.7098 from Graham & Mortimer (1992)). No strontium isotopic data exist for the Alpine Schist in this area to enable a more direct comparison.…”

“…Metamorphic grade rises from zeolite or prehnite-pumpellyite facies to sub-biotite zone from the east coast of New Zealand to the Main Divide of the Southern Alps. Geochronologic studies of these low-grade rocks reveal relatively undisturbed K-Ar and Rb-Sr ages, which constrain the age of Rangitata metamorphism as Early Jurassic to mid Cretaceous Graham & Mortimer 1992;Adams & Robinson 1993). Determining the timing of thermal events associated with the later Kaikoura Orogeny, however, has been more problematic.…”

Age/isotopic characterisation of the Waipapa Group in Northland and Auckland, New Zealand, and implications for the status of the Waipapa Terrane

“…Although not diagnostic, Caples Group K-Ar ages are also 160-190 Ma (C. J. Adams & J. E. Gabites unpubl. data; Graham & Mortimer 1992;Adams & Robinson 1993). The OmahutaPuketi unit falls immediately east of the JMA (Fig.…”

“…The Omahuta-Puketi (t)-(i) data (Table 3, sets 1-3) are closely grouped, and similar to those for Caples Terrane in the South Island (Graham & Mortimer 1992;Adams & Graham 1997;Adams et al 1999), but they can only be defined as a subset, generally the least radiogenic, of the full Waipapa Group dataset (Fig. 5A).…”

Tracing the Caples Terrane through New Zealand using detrital zircon age patterns and radiogenic isotope signatures

“…The ordering of formation names is that implied by the detrital zircon age data (this work). regional metamorphism (Graham & mortimer 1992;Adams & Robinson 1993;Coombs et al 2000). in Otago, Canterbury, and marlborough, these low-grade metasediments pass into medium to high-grade greenschist-facies schists (Haast Schist), which retain geochemical evidence of Caples/ Pelorus ancestry (mortimer & Roser 1992 Graham & mortimer 1992;Adams & Graham 1997;Adams et al 1999).…”