Abstract
A younger age limit to high-grade metamorphism in part of western Fiordland, New Zealand, is obtained from an unmetamorphosed hornblende gabbro that intrudes kyanite-margarite-bearing amphibolite in the mountains east of George Sound. Laser ablation ICP-MS analyses and cathodoluminescence imaging show that zircon grains from the hornblende gabbro form two distinct populations: (1) brightly luminescent grains with a pooled age of 345.8+ or -2.9 Ma and dully luminescent rims, and (2) dully luminescent whole grains with a pooled age of 118.5+ or -1.2 Ma. On the basis of a lack of metamorphic assemblages, and distinct zircon rare earth element concentrations, the hornblende gabbro is interpreted to have been emplaced at 118.5+ or -1.2 Ma. This age puts a younger limit to kyanite grade metamorphism in this area and demonstrates that it did not re-equilibrate during subsequent extension, as has been suggested for other parts of Fiordland.