Beehive Diorite: A Late Jurassic two‐pyroxene pluton at Lake Manapouri, Fiordland

Abstract

Beehive Diorite is a small but distinctive two‐pyroxene pluton exposed amongst the heterogeneous Hunter Intrusives on the shoreline of Lake Manapouri in Fiordland, New Zealand. This 149 Ma pluton has been partially re‐hydrated and deformed to amphibole‐bearing meta‐diorite, but contains relict hypersthene‐augite primary assemblages in low strain domains. Mafic and felsic dikes that intrude Beehive Diorite recrystallised under amphibolite and then greenschist facies conditions. Geochemical composition indicates that Beehive Diorite is a calc‐alkaline cumulate derived from a primitive source in a volcanic arc setting, and provides a baseline for Darran Suite mafic magmatism at Lake Manapouri. The crosscutting mafic dikes also belong to the Darran Suite, but the felsic dikes belong to the Separation Point Suite. Beehive Diorite is petro graphic ally and geochemically similar to Hollyford Gabbronorite, and diorite at Mt Underwood in northern Fiordland. This correlation indicates that subduction‐related processes in the Outboard Median Batholith remained dominant from 149 to 138 Ma, but contrasts with slightly younger and older A‐type magmatic pulses, which suggest short periods of slab rollback or stalling. Amphibolite facies metamorphism of Beehive Diorite and the crosscutting dikes occurred between 124 and 116 Ma, after the cessation of Darran Suite and initiation of Separation Point Suite magmatism.