STRATIGRAPHY AND TECTONIC SETTING OF THE CALLIOPE-VOLCANIC-ASSEMBLAGE, ROCKHAMPTON AREA, QUEENSLAND

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 Roc khampton region, three stratigraphic units are recognized: the Early D evonian Mt Holly Formation and the Middle Devonian Capella Creek and B armundoo Formations, with the Mt Morgan Tonalite (Late Devonian) consi dered as part of the assemblage. Trace element data for the volcanic r ocks, ranging from basalt through andesite to dacite and rhyolite, ind icate that they formed in a volcanic arc. The Mt Holly and Capella Cre ek Formations (mostly coarse volcaniclastic rocks) were deposited main ly in a shelf environment fringing the arc. Modal analyses indicate th at the Mt Holly Formation formed more distally than the Capella Creek Formation. The Barmundoo Formation (thin-bedded sandstone and siltston e) formed in deeper water to the east, probably in a fore-arc basin, a nd 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 tha t 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 t he Late Devonian corresponding to an unconformity. It is possible that the Calliope Volcanic Assemblage formed on the Australian continent r ather than being an exotic terrane.