Rb‐Sr dating of Rahu Suite granitoids from the Paparoa Range North Westland, New Zealand

Mapping in the central Paparoa Range, West Coast of the South Island, New Zealand, has led to the recognition of three petrologically distinct granitoids. These are Steele Granodiorite, Blackwater Granite, and Buckland Granite, which were intruded in that order into the Charleston Metamorphic Group and Greenland Group in mid‐Cretaceous times. Mineralogy, whole‐rock chemistry, and Sr isotopic composition suggest that all three granitoids belong to the intermediate I/S‐type Rahu Suite. Rb‐Sr whole‐rock geochronology provides an intrusive age of 116 ± 6 Ma for Buckland Granite, but is unable to establish the intrusive age of the other two granitoids. Significant1y younger muscovite ages (103–112 Ma) and biotite ages (92–99 Ma) indicate immediate postintrusive uplift of all three granitoids in the order of 0.5‐1.0 mm/a. Fieldevidence suggests that Buckland Granite was intruded in several batches. The wide range of initial 87 Sr/ 86 Sr (0.7058–0.7094) indicates at least two isotopically different source components. Isotopic variation in some Blackwater Granite samples is attributed to low‐temperature alteration associated with lamprophyre dike intrusion whereas similar variation in some Steele Granodiorite samples is due to contamination by metasedimentary gneiss.