Temporal development of the Atherton Basalt Province, north Queensland

Abstract

The Atherton Basalt Province is centred on the Atherton Tableland, ∼50 km southwest of Cairns in north Queensland. Forty-eight K – Ar age determinations and four U/Th analyses from these basalts provide information on the distribution of the volcanics over time. Volcanism commenced at 7.1 Ma and continued into the Early Holocene, with volumetric peaks in activity occurring 3.5 – 3 Ma and 2 – 1 Ma. The province shows a change with time from eruptions of voluminous lava flows that built relatively large shield volcanoes, to the production of less voluminous lavas and pyroclastics associated with cinder cones during the last million years. Phreatomagmatic, maar-forming eruptions are also preserved among the most recent eruptions. Previous radiocarbon dating of swamp sediments suggested that volcanic activity may have occurred within the past 10 000 years. No systematic change over time is apparent in the location of the volcanoes of the province. Rather, a source region ∼80 km in diameter for the province as a whole has evolved over time. Extensive partial melting in the upper mantle may have led to the ascent and adiabatic melting of lesser volumes of mantle material from deeper levels. Changes in lithospheric stresses in north Queensland, caused by the docking of the Ontong Java Plateau and subsequent development of northward subduction at the San Cristobal Trench, may have allowed the ascent of magma from this mantle region.

Key words:

• Atherton Basalt Province
• basalt
• Cenozoic
• potassium – argon dating
• Queensland
• uranium – thorium dating
• volcanology

Acknowledgements

We thank landholders in the region for access to their properties. Some of the new K/Ar dates in this paper were funded by grants from the ARC. Some of the localities were visited during excursions run by the North Queensland Geological Society, and Karl Seelig is thanked for the organisation of these excursions and the resulting discussions. The financial support of CSIRO and the Rainforest CRC, and the collaborative CSIRO/UQ research relationship is gratefully acknowledged for the U/Th dating. A. D. C. Robertson (deceased), L. Barron and J. Barron provided advice during fieldwork on selection of basalt samples for U/Th dating. We thank R. J. Bultitude and F. L. Sutherland for their helpful comments in reviewing this paper.