POTENTIAL FIELD CHARACTERISTICS OF A PROTEROZOIC LARGE FELSIC IGNEOUS PROVINCE: CURNAMONA PROVINCE, AUSTRALIA

The Paleoproterozoic Curnamona Province stands out as one of the most geophysically distinct terranes on the Australian continent. The internal geophysical response is complicated, reflecting a combination of distribution of magnetite-bearing rocks, depth to basement and the intensity of deformation and magmatism. In the core of the province, the dominantly acid Benagerie Volcanics overlie basement deformed during the ca. 1600-1590 Ma Olarian Orogeny. This volcanic province is not exposed and has only been intercepted by sparse drillholes, however it can be identified in regional geophysical datasets. Aeromagnetic data shows the aerial extent of this volcanic province to be 90 x 110 km (i.e., 9900 km2), distinguishable from basement rocks by its characteristic stippled, cross-hatched textural pattern, which is enhanced in both the 1st vertical derivative of the total magnetic intensity data as well as in colour drape, sun angle images. This magnetic texture reflects the heterogeneous distribution of magnetite within the Benagerie Volcanics. The stark contrast between this texture and a more smoothly varying magnetic field creates well-defined and hence easily observed magnetic boundaries to the province. This characteristic magnetic pattern coincides with a negative (-270 g.u.) Bouguer gravity anomaly of similar extent. Specifically, the eastern boundary of the magnetic province is coincident with a sharp regional Bouguer gravity gradient which decreases westwards at a rate of 5.4 g.u. km-1. The source of the gravity anomaly is interpreted as a large felsic pluton coeval to and underlying this volcanic province. The geophysical response of the Benagerie Volcanics is similar to the contemporaneous Gawler Range Volcanics in the adjacent Gawler Craton. These magmatic rocks are interpreted as separate parts of a larger felsic igneous province that formed in response to the arrival of a mantle plume at ca. 1590-1580 Ma.