Stratigraphy and tectonic setting of the Calliope Volcanic Assemblage, Rockhampton area, Queensland

Abstract

The Calliope Volcanic Assemblage, ranging from Late Silurian to Middle Devonian, is dominated by shallow marine volcaniclastic deposits and limestone, with small amounts of primary volcanic material. In the Rockhampton region, three stratigraphic units are recognized: the Early Devonian Mt Holly Formation and the Middle Devonian Capella Creek and Barmundoo Formations, with the Mt Morgan Tonalite (Late Devonian) considered as part of the assemblage.

Trace element data for the volcanic rocks, ranging from basalt through andesite to dacite and rhyolite, indicate that they formed in a volcanic arc. The Mt Holly and Capella Creek Formations (mostly coarse volcaniclastic rocks) were deposited mainly in a shelf environment fringing the arc. Modal analyses indicate that the Mt Holly Formation formed more distally than the Capella Creek Formation. The Barmundoo Formation (thin‐bedded sandstone and siltstone) formed in deeper water to the east, probably in a fore‐arc basin, and the Mt Morgan Tonalite is a high level arc pluton. This arrangement suggests the arc faced east.

The abundance of silicic volcanic rocks and presence of detrital muscovite and local quartzarenite suggest that the arc was either built on thin continental crust, or was a mature island arc close to a continent. Volcanism was almost continuous from the Early Devonian to the Early Carboniferous, with a short break in the Late Devonian corresponding to an unconformity. It is possible that the Calliope Volcanic Assemblage formed on the Australian continent rather than being an exotic terrane.

Key words:

• Calliope Volcanic Assemblage
• Devonian
• fore‐arc basin
• New England Fold Belt
• volcanic arc

Notes

Present address: Department of Geology, Ballarat University College, PO Box 663, Ballarat, Vic. 3353, Australia.