New U-Pb zircon ages for the Glenroy Complex and McKnee Intrusives, southeast Nelson : strengthening links with northern Fiordland and constraining the timing of metamorphism

The Glenroy Complex and McKnee Intrusives, southeast Nelson, have previously been correlated with similar rocks in northern Fiordland: the Worsley Pluton of the Western Fiordland Orthogneiss and George Sound Paragneiss, and Mistake Diorite and Darran Leucogabbro, respectively. Two samples of the Glenroy Complex (Woodham Orthogneiss) and one from the McKnee Intrusives yielded laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon ages of 123.7±1.4 and 121.9±1.1 Ma, and 138.8±1.3 Ma, respectively. These new ages fall within the ranges previously published for the Glenroy Complex, McKnee Intrusives and their northern Fiordland counterparts and, thus, provide further evidence for their correlation. An age of 116.3±2.4 Ma was also determined for a post-metamorphic pegmatite–aplite dike, constraining metamorphism of the Woodham Orthogneiss to within 2.0-9.0 Ma following magmatic crystallisation. The time gap between crystallisation and metamorphism is similar to that of the Worsley Pluton (3.7-8.9 Ma), lending additional support for their direct correlation. (author)