Structure and Evolution of the Volcanic Cauldrons, Ring Complexes and Associated Granites of the Georgetown Inlier, Queensland

Abstract

THE Georgetown Inlier in North Queensland covers an area of about 37,000 square miles and lies on the western flank of the Palaeozoic Tasman Geosynclinal Zone (Fig. 1). It consists largely of Pre-Cambrian metamorphic and granitic rocks, and a suite of Upper Palaeozoic acid igneous rocks. The Upper Palaeozoic acid igneous rocks, which occupy an area of about 10,000 square miles, include extensive acid volcanics and associated granitic intrusions, and form a well-defined petrographic province¹. The volcanic rocks consist predominantly of rhyodacite² welded tuff³ with subordinate rhyolite, trachyandesite, andesite and basalt, belonging to the calc-alkaline rock series. The intrusive rocks are mainly adamellite² with subordinate granite and grano-diorite.