K-Ar geochronology of Torlesse Supergroup metasedimentary rocks in Canterbury, New Zealand

K-Ar ages of 144 slates and semischists are reported from the Torlesse Supergroup, mostly in the Canterbury region. From local schist enclaves at upper prchnite-pumpellyite to pumpellyite-actinolite mineral facies, K-Ar ages are compared of intercalated mudstone protolithologies of continent-derived turbidite, and oceanic-derived pelagic/volcanic, associations. These reveal metamorphism sufficiently thorough to reset detrital K-bearing mineral components in the former. Two main events are separately recorded within the Late Permian and Middle-Late Triassic parts of the Torlesse accretionary prism, respectively at 240 +/- 10 Ma (Early Triassic) and 210 +/- 10 Ma (latest Triassic to earliest Jurassic). The Early Triassic metamorphism is correlated with a stratigraphic break in the Torlesse succession, which reflects a period of non-deposition and possibly uplift. The pattern of Late Triassic-Early Jurassic metamorphism, and subsequent younger, cooling ages, is similar to those of Triassic Torlesse sequences in North Otago and Wellington regions, and they are also correlated with a major, Early-Middle Jurassic, stratigraphic break. The Jurassic Clent Hills Group may represent a local Rakaia Terrane cover sequence on the earlier-consolidated parts of the accretionary prism, whilst elsewhere, in the Pahau Terrane, Late Jurassic-Early Cretaceous Torlesse sedimentation recommenced.