Abstract
A segment of the Brookstreet terrain (Coombs et. al., 1976) is described from the Bluff Peninsula, Southlando The basement rocks include Lower-Permian volcanogenic sediments and dykes of the Greenhills Group with interbedded calcarenites and flows. The rocks are steeply dipping and are locally deformed into open, steeply-plunging folds. An intrusive body of gabbronorite with associated late-stage derivatives occurs in the Southern part of the area and is surrounded by a translation zone of partially assimilated metasediment and a wide metamorphic aureole. The metamorphic grade of' the country rock is predominantly hornblende-hornfels facies but locally increases to pyroxene-hornfels facies. The gabbronorite is intruded along the Western coastline by a suite of quartz diorite and granitic dykes. Temperature estimates for the intrusive rocks are included and are derived from experimental data and microprobe analysis of pyroxene and magnetite-ilmenite pairs respectively. A cryptic variation trend in the gabbronorite is investigated. Previous geologic work on the Bluff Peninsula is summarised and the mutual relationships and possible genesis of the various intrusive bodies is discussed.