The northern headland at Boat Harbour (near Port Stephens NSW, Australia) is dominated by a massive ignimbrite layer of late Carboniferous age. The ignimbrite is rhyodacitic in composition and was formed by a large volcanic ash flow. The volcanics are intruded by a vertical mafic dyke with a near north-south strike. The dyke reaches ~2 metres in maximum thickness. A smaller second mafic dyke can be seen to the west of the main dyke. The dyke continues to the north and crops out at Morna Point and the headland at the southern end of One Mile Beach (a distance of 950 metres). While we are unsure of the age of the dykes, others nearby dykes of similar orientation and composition have been dated as Permian. An outcrop scale model is available here.
Comments