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

Abstract

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.

澳大利亚东部新生代火山活动量曾根据玄武岩出露程度而估计过，但后来钻孔显示地下火山流具高达60米的累积厚度。因此，新生代岩浆的量级比以前所认为的大得多，从而使得有必要进行玄武岩分布的重新评价并估计喷发量。钻井数据收集自澳大利亚东部Bowen盆地以编制区域玄武岩等厚图。这个庞大数据，包括150000个钻孔日志，被用来推算火山喷出最小估计量：Peak Range火山约2600立方公里；Springsure 火山约1460立方公里；Buckland火山约860立方公里。这些火山的喷发量向南减少，以及喷发速率向南递减，最有可能原于热柱岩浆的减弱。我们估计，从约30Ma（昆士兰州Peak Range火山的平均年龄）至约10Ma（新南威尔士州的Canobolas火山大约年龄），在东澳大利亚中部火山喷发速率下降了大约15立方公里/百万年。此外，我们的数据表明，在澳大利亚东部，玄武岩流填充了早先存在的通道，最大深度范围为60至220米，意味着早期到中期新生代地形为中等起伏。

KEY WORDS:

• basalt
• mantle plume
• east Australia
• Bowen Basin
• eruption rate
• Cenozoic volcanism

ACKNOWLEDGEMENTS

This work was supported by the Australian Coal Association Research Program [Project C22023]. We would like to thank the Australian Coal Association Research Program and mining companies of the Bowen Basin for their contributions to the drill-hole database, without which this research would not have been possible. We would also like to thank Tracey Crossingham and Kurt Knesel for their assistance and support of the project. The paper benefitted from reviews by Robert Kitch and Lin Sutherland.