Basalt distribution and volume estimates of Cenozoic volcanism in the Bowen Basin region of eastern Australia: Implications for a waning mantle plume

The volume of Cenozoic volcanism in eastern Australia has been estimated previously from the outcrop extent of basalts, but drill holes have subsequently revealed subsurface volcanic flows with a cumulative thickness of up to 60 m. The magnitude of Cenozoic magmatism is therefore greater than previously thought, necessitating a re-evaluation of basalt distribution and estimates of eruptive volumes. Drill-hole data were collected from across the Bowen Basin in eastern Australia to compile a regional basalt isopach map. This large dataset comprising ∼150 000 drill-hole logs was used to derive minimum extrusive volume estimates of the Peak Range, Springsure and Buckland volcanoes of approximately 2600 km³, 1460 km³ and 860 km³, respectively. The southward decrease in the volumes of these volcanoes, as well as a southward diminishing pattern of eruption rate, most likely arose from waning plume magmatism. We estimate that from ca 30 Ma (the average age of the Peak Range volcano in Queensland) to ca 10 Ma (the approximate age of the Canobolas volcano in New South Wales), the eruption rate in the east Australian central volcanoes decreased by roughly 15 km³/Ma. Additionally, our dataset suggests that basalt flows in portions of eastern Australia filled pre-existing channels with maximum depths ranging from 60 to 220 m, implying an early- to mid-Cenozoic topography of moderate relief.