Microcline megacrysts from the green lake granodiorite, eastern fiordland, new zealand

Abstract

An early magmatic and high temperature origin is suggested for microcline megacrysts from a granodiorite batholith which crops out near Green Lake, eastern Fiordland, New Zealand. The evidence for the nature of their origin is: the enrichment of Ba in the cores of the microcline megacrysts compared to groundmass microcline; application of a newly proposed two-feldspar geothermometer suggests a high temperature origin; consideration of the size and shape of the megacryst; the internal texture of the megacryst; and the lack of metasomatic features. The occurrence of the micro cline rnegacryst in the granodiorite batholith outcropping in the Green Lake area indicates that unusually high pressure and temperature as well as high water contents were involved in the early history of crystallisation of the batholith. © 1977 Taylor & Francis Group, LLC.