STRATIGRAPHY, AGE RELATIONSHIPS AND TECTONIC SETTING OF RIFT-PHASE INFILL IN THE DRUMMOND BASIN, CENTRAL QUEENSLAND

The Drummond Basin represents a major, backarc extensional system loca ted at the inboard margin of the northern New England Orogen. Its synr ift (cycle 1) infill is distinctively volcanic and volcaniclastic in c haracter and displays complex facies relationships and considerable va riations in thickness controlled by the history and fabric of extensio nal faulting and the distribution of coeval volcanic centres. Subtle i nheritance signatures in the age spectra obtained by SHRIMP (II) Pb-U dating of zircons from volcanic units have impeded age assignment. New geochronologic data indicate that basinal subsidence was initiated in the north in latest Devonian (Famennian) time but was delayed until t he Early Carboniferous (Tournaisian) in the south. Northern succession s ore dominated by volcaniclastic strata that accumulated distal to th e loci of contemporary volcanism, whereas southern successions are dom inated by silicic flows and ash-flow tuffs and associated hypabyssal i ntrusive suites proximal to, or coincident with, volcanic loci, The Bu rdekin, Clarke River and Bundock Creek Basins located north of the Dru mmond Basin are broadly coeval features with comparable infill. They l ikewise represent backarc basins developed inboard of the northern New England Orogen which trends offshore at latitude 20 degrees S and app ears to be represented in basement cores recovered from the Coral Sea. Calc-alkallne magmatism of Late Devonian-Early Carboniferous age exte nded at least 400 km inboard of the Gondwanan plate margin now represe nted in Queensland and related to an acute angle of subduction along t he active margin at that time.