Emplacement ages of granitic rocks in the Coen Inlier (Cape York): implications for local geological evolution and regional correlation

New zircon ion-microprobe U-Pb analyses define two major, short-lived episodes of Palaeozoic magmatism within the Coen Inlier, north Queensland. The younger occurred at about 284 Ma, when the Weymouth Granite and Twin Humps Adamellite were emplaced. Previously published younger K-Ar ages for this event are probably a consequence of radiogenic Ar loss from chlorite-rich biotite concentrates. Most of the granites in the inlier were emplaced during a brief intrusive episode in the Late Silurian - Early Devonian. Restitic (or xenocrystic) zircon ages and Sm-Nd isotopic data are consistent with the derivation of both generations of granites from Precambrian crustal components similar to those which produced granites of closely similar ages in the Georgetown Inlier. Tectonothermal activity at ~1600 Ma was probably part of quasi-continuous activity extending over several hundred million years. A 2500 Ma crustal component is also identified. Although the metasedimentary rocks of the Coen Inlier were derived from weathering and erosion of a Precambrian terrane, the current isotopic data cannot discriminate between Proterozoic. Early Palaeozoic and even Middle Palaeozoic ages of deposition for the metamorphosed sedimentary rocks.