Observations on the geology of an area near lakes Thomson and Hankinson, Fiordland

85 The physiography of the area is dominated by glaciated landforms carved in gneiss of the Fiordland Complex. The gneiss is generally dioritic, with gradations to quartzo-feldspathic and amphibolitic varieties, and is cut by mainly barren pegmatite veins; epidote is abundant. The rocks commonly show signs of post-consolidational shearing and crushing. There is a well defined zone of strongly crushed rocks, trend· ing approximately north, which cuts obliquely across the northern end of Lake Hankinson. In general the rocks are petrographically similar to those near Lake Manapouri. Chemical analyses of a microcline-bearing gneiss, a hornblende-biotite gneiss, and an amphibolite are compatible with derivation of these from acid and intermediate volcanic or tuffaceous sedimentary rocks and mildly alkaline olivine basalts respectively. Geometric analysis of foliation attitudes, lineations, and minor fold axes, shows that there is a statistical fold axis plunging gently to the south-west.