A Granite-Schist Contact in Stewart Island, New Zealand

Abstract

I. Introduction Stewart Island is a rugged and almost uninhabited island lying off the southern coast of New Zealand. It is densely forested, but along the summits of the bleak wind-swept highlands, which are constantly buried in cloud, the thick bush gives way to scrub and tussock, and some bare rock-surfaces are exposed. The granite peaks of Stewart Island expose sections of an extensive granite batholith, which makes up the greater part of the island and probably extends 60 miles south to the desolate Snares Islands and 70 miles north-west to the fiord country of the South Island of New Zealand. The granite invaded a biotite-muscovite-schist with interlaminated quartzite, a chloritized kyanite-amphibole-schist, and a calc-silicate-hornfels. All these rock types occur as small pendants in the granite (see map, Pl. XI), but the mica-schist predominates. The object of the paper is to discuss the origin of the mica-schist, the manner in which it was dispersed to give place to magma, and the mineralogical changes produced in both the granite and the schist by reaction between these rocks and the fugitive constituents of the magma. Where relevant, passing mention will be made of the calcareous rocks. The fugitive substances were reactive at two periods: (1) prior to the ascent of the main intrusion, when gases passed into the roof of the batholith and either contributed to the formation of the micas of the schist or were responsible for the persistence of the micas into the innermost aureole; and (2) subsequent to the