The Canobolas complex, N.S.W., an alkaline shield volcano

Abstract

Abstract The partly eroded remains of a Miocene compound shield volcano crop out near Orange, central New South Wales. A cluster of conical and domical landforms occupies the central elevated core of the volcano, and they are usually surrounded by flows of more basic lava that radiate out from this centre. At the present level of erosion, trachyte, and in particular ferroaugite trachyte, is the most abundant type of rock in the core of the complex, whereas hawaiite is the dominant type of rock in the outer part. Other rocks in the central area include mugearites, benmoreites, comendites, and a wide variety of pyroclastic rocks. The pyroxenes in the hawaiite‐trachyte suite range from Mg‐rich augite to ferrohedenbergite. Arfvedsonite is the characteristic mafic phase in the comendites. All the rocks of the complex are part of a single comagmatic suite. It is proposed that the magmas that formed most of the mugearites, benmoreites, trachytes and comendites evolved at relatively low pressures in a large compo...