Decompression melting driving intraplate volcanism in Australia: Evidence from magnetotelluric sounding

A long-period magnetotelluric (MT) survey, with 39 sites covering an area of 270 by 150 km, has identified melt within the thinned lithosphere of Pleistocene-Holocene Newer Volcanics Province (NVP) in southeast Australia, which has been variously attributed to mantle plume activity or edge-driven mantle convection. Two-dimensional inversions from the MT array imaged a low-resistivity anomaly (10-30Ωm) beneath the NVP at ∼40-80 km depth, which is consistent with the presence of ∼1.5-4% partial melt in the lithosphere, but inconsistent with elevated iron content, metasomatism products or a hot spot. The conductive zone is located within thin juvenile oceanic mantle lithosphere, which was accreted onto thicker Proterozoic continental mantle lithosphere. We propose that the NVP owes its origin to decompression melting within the asthenosphere, promoted by lithospheric thickness variations in conjunction with rapid shear, where asthenospheric material is drawn by shear flow at a "step" at the base of the lithosphere.

Eruption centres of the Hamilton area of the Newer Volcanics Province, Victoria, Australia: Pinpointing volcanoes from a multifaceted approach to landform mapping

Volcanic eruption centres of the mostly 4.5 Ma-5000 BP Newer Volcanics Province in the Hamilton area of southeastern Australia were examined in detail using a multifaceted approach, including ground truthing and analysis of ArcGIS Total Magnetic Intensity and seamless geology data, NASA Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) digital elevation models and Google Earth satellite image interpretation. Sixteen eruption centres were recognised in the Hamilton area, including three previously unrecorded volcanoes-one of which, the Cas Maar, constitutes the northernmost maar-cone volcanic complex in the Western Plains subprovince. Seven previously allocated eruption centres were placed into question based on field and laboratory observations. Three phases of volcanic activity have been suggested by other authors and are interpreted to correlate with ages of >4 Ma, ca 2 Ma and <0.5 Ma, which may be further subdivided based on preservation of outcrop. Geochemical compositions of the dominantly basaltic products become increasingly alkaline and enriched in incompatible elements from Phases 1 to 2, with Phase 3 eruptions both covering the entire geochemical range and extending into increasingly enriched compositions. This research highlights the importance of a multifaceted approach to landform mapping and demonstrates that additional volcanic centres may yet be discovered in the Newer Volcanics Province

Victoria erupts: The Newer Volcanics Province of south-eastern Australia

The Newer Volcanics Province of south-eastern Australia is often overlooked, though it comprises a multitude of volcanic features worthy of exploration. The province contains > 416 eruption centres varying in nature from simple to complex, ranging from lava shields and scoria cones to some of the largest maar volcanoes in the world. Explorable caves and lava tubes showcase well-preserved lava flow features, while the province is a fossickers dream, containing abundant mantle xenolith and megacryst collecting localities. As the most recent eruption was ~5000 bp at Mt. Gambier, the Newer Volcanics is considered an active province, and may yet provide Australia with more eruptions, adding to the glorious volcanic features of the wonderful landscape.