The Granite-Gneisses of Southern Eyre Peninsula (South Australia) and their Associated Amphibolites

Abstract

I. Introduction. The basement platform which forms the foundation of Southern Eyre Peninsula, and on which the much younger Tertiary and Recent sediments repose, consists of a complex of igneous and metamorphic rocks, which in their lithological and petrographical characters bear not only a remarkable resemblance to rocks of known Pre-Cambrian age in other parts of the State, but also to the well-known Pre-Cambrian tracts in other regions of the world. The evidences for the Pre-Cambrian age of the Eyre Peninsula rocks cannot rest on palaeontological evidence, for there are no known deposits of Lower Palaeozoic age that have been recognized within the area. The data from which the Pre-Cambrian age is deduced are, therefore, of a comparative kind. The older rock series of Yorke Peninsula to which these Eyrian rocks bear a close lithological and petrographical resemblance are of definite Pre-Cambrian age, as proved by the presence of Cambrian sediments on an eroded platform of the series, in the Moonta and Wallaroo region. Apart from this local correlation, the complex bears a noteworthy similarity to the Pre-Cambrian tracts of the Northern Hemisphere, and to none more than the Laurentian of Canada. Superposed with a marked angular unconformity on the meta-morphosed members of this older complex, and resting horizontally on the deeply-eroded igneous types, are Upper Tertiary sands and travertine. These deposits form a mantle to a considerable portion of the region, and hinder the study of the older series over large areas of country. Inland, in the hilly regions