The late Permian shoshonitic province of the southern Sydney Basin

The Late Permian shoshonitic province of the southern Sydney Basin comprises extrusions and intrusions which have present exposures confined to the 140 km of coastal region between Durras and Wollongong but geophysical and sedimentological data suggest extension of the province offshore from Wollongong for approximately 200 km to the northeast. Nine extrusive units comprising five basalts, three basaltic andesites and an andesite have been recognized. Late Permian intrusions can be grouped into three major intrusive complexes comprising the Termeil, Milton and Coonemia Complexes, and small sills at Stockyard Mountain and Towradgi. The Termeil Complex consists of a stock of monzogabbro and related basalt dykes and sills whereas the Milton Complex comprises monzonitic sills and a layered monzonitic stock formed by multiple intrusion. The Coonemia Complex is composed of numerous dykes and sills and a layered laccolith of monzonite (upper zone) and porphyritic monzogabbro (lower zone) which was formed by in situ differentiation of a basic magma now represented by the upper and lower border zones. The Late Permian age of the extrusions is indicated by biostratigraphic, palaeomagnetic and K-Ar data whereas the age of the intrusive rocks is based on K-Ar data and similarity in petrography and geochemistry to dated rocks.