Stratigraphy, age relationships and tectonic setting of rift‐phase infill in the Drummond Basin, central Queensland

Abstract

The Drummond Basin represents a major, backarc extensional system located at the inboard margin of the northern New England Orogen. Its synrift (cycle 1) infill is distinctively volcanic and volcani‐clastic in character and displays complex facies relationships and considerable variations in thickness controlled by the history and fabric of extensional faulting and the distribution of coeval volcanic centres. Subtle inheritance 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 the Early Carboniferous (Tournaisian) in the south. Northern successions are dominated by volcaniclastic strata that accumulated distal to the loci of contemporary volcanism, whereas southern successions are dominated by silicic flows and ash‐flow tuffs and associated hypabyssal intrusive suites proximal to, or coincident with, volcanic loci. The Burdekin, Clarke River and Bundock Creek Basins located north of the Drummond Basin are broadly coeval features with comparable Infill. They likewise represent backarc basins developed inboard of the northern New England Orogen which trends offshore at latitude 20°S and appears to be represented in basement cores recovered from the Coral Sea. Calc‐alkaline magmatism of Late Devonian‐Early Carboniferous age extended at least 400 km inboard of the Gondwanan plate margin now represented in Queensland and related to an acute angle of subduction along the active margin at that time. Show more