Carboniferous and Permian granites of the northern Tasman orogenic belt, Queensland, Australia: insights into petrogenesis and crustal evolution from an in situ zircon study

Abstract

In situ U–Pb dating and Lu–Hf systematics of zircon in granites of the Hodgkinson Province in the northern Tasman orogenic belt, Queensland, Australia, reveal input of isotopically more evolved crustal magmas and larger ranges in 176Hf/177Hf in the Carboniferous I-type granites (0.28219–0.28269; weighted average ~0.28245) than in the Permian S-type granites (0.28249–0.28280; weighted average ~0.28262) and Permian I-type granites (0.28253–0.28274; weighted average ~0.28260). The wide range in the Hf-isotope compositions of zircons in the Carboniferous and Permian granites can be explained by remelting of a heterogeneous Mesoproterozoic crustal source, whereas a narrow range reflects the subsequent dissolution of inherited grains/cores and magma homogenisation before zircon crystallisation. Alternatively, mixing between the most radiogenic and unradiogenic magmas can produce the isotopic variation seen in other Carboniferous granites. Remelting of Neoproterozoic average crust or mafic younger crust can produce the more radiogenic Hf-isotope compositions of zircons in the Permian S-type granites. An overlap between the Hf-isotope signatures of the Carboniferous I-type granites in the southwestern Hodgkinson Province and the northeastern Australian craton (0.28211–0.28254) and evidence for major magmatic events at 1,585–1,545 and 345–300 Ma imply that the southwestern province is underlain by cratonic crust, which wedges out towards the northeast. The more radiogenic Hf-isotope signature of the Permian granites and a lack of evidence for these major magmatic events in the southeastern and central Hodgkinson Province imply that these parts are characterised by different crustal sources and crustal evolution histories.