Sutherland Frederick L.1, Graham Ian T.2
1Geosciences, Australian Museum, 1 William Street, Sydney, NSW 2010, Australia; 2School of Biological Earth and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia
East Gondwanan Cretaceous late Mesozoic thermal rifting initiated near-continuous Australian intraplate basaltic volcanism that inevitably will continue. Researchers mostly expect that the next eruption will likely occur within the young SW Victoria-SE South Australia or NE Queensland basalt fields. These areas preserve many eruptive features, although the southern fields seem past peak activity, while the northern fields seem closer to peak activity. This presentation looks beyond these areas and examines isolated eruptive events within the last 5 Ma elsewhere throughout Eastern Australia. These sites forecast that a new volcano may well erupt in an unexpected area.
Queensland: Young isolated basalt sites include 3.7 Ma nephelinites at Silver Plains, over 200 km NW of the main NE Queensland basalt provinces. These fields have been linked to a cryptic mantle plume below the adjacent Coral Sea floor. The isolated South Barnard offshore islands are ~ I Ma old pyroclastic cones and intrusive dykes, SE of the main Atherton basaltic field. A further eruption there would create shallow marine explosive activity. Mount St Martin, northern Bowen Basin, is a unique isolated 2.4 – 3.1 Ma lava-capped pyroclastic vent of hybrid basanite-trachyte, much younger than adjacent basalts and rhyolites of the Nebo Province. In western Qld, in the Winton-Longreach region, 3He/4He and 87Sr/86Sr studies on ground water discharges and an underlying slow seismic anomaly suggested sub-surface cooling basaltic intrusions. In SE Qld, an age-decreasing trend of isolated young basaltic fields extends 200 km SW from Bundaberg to Brigooda. It predicts potential further eruption to the SW, but this may depend on the lithospheric depth.
New South Wales: Young 2 – 5 Ma reset zircon megacrysts eroded from basaltic eruptives fringe outskirts of older basaltic areas in several regions. In rare cases they occur in diatremes, as at Gloucester River, SW of Barrington Tops shield volcano. Otherwise, they concentrate in alluvial deposits on the eastern flank of that volcano. In Tobins Camp lead SE of Yarrowitch, 2.7 Ma zircons in the isolated deposit are 40 Ma younger than adjacent Yarrowitch basalts. At Oban and Uralla, 2 – 3 Ma zircons are ~20 Ma younger than adjacent basalts. In SW NSW, bentonite ash beds in 1.6 – 2.4 Ma Murray Basin strata at Arumpo seem linked to proximal eruptive sites.
Victoria: In eastern Victoria, the Uplands basalts incude 2 and 4 Ma flow events, while to the NW near Toombullup alluvial deposits contain 2 Ma reset zircons.
Tasmania-West Tasman Sea: Mantle CO2 discharges in NW Tasmania and seismic activity east of Flinders Island and in the Central Tasman Sea floor mark predicted dormant plume positions for the East Australian plume array. Recent research voyages have now located young sea mounts at the predicted plume nodes for the Tasmantid and Lord Howe seamount chains.
Summary: These widespread young activities offer a complex dynamic scenario for future eruptions.
Frederick Lin Sutherland, BSc (Hons), MSc (Univ.Tasmania), PhD (James Cook Univ.), worked at Queen Victoria Museum, Tasmanian Museum in Tasmania, James Cook Univ., Townsville, Qld, The Australian Museum, Univ. Western Sydney, now Senior Fellow, Geosciences, Australian Museum. Researches involve igneous rocks, Australian Geology, gemstones, zeolitic suites, mass extinctions.