Adakitic Permian magmatism along the eastern Gondwana margin: constraints on deep crustal processes and metallogenesis in northeastern Queensland
Abstract
Abstract The Kennedy Igneous Association (KIA) of northeastern Queensland provides an opportunity to investigate links between granitoid magmatism, deep crustal processes and metallogenesis along the eastern Gondwana margin. This study integrates whole-rock geochemistry with new zircon U–Pb geochronology to constrain the timing, sources and tectonic significance of granitoids from the Georgetown region (Kidston subprovince). Igneous rocks are divided into a Permian group and a Carboniferous group. Zircon U–Pb ages define two principal magmatic episodes: early Carboniferous magmatism (360–333 Ma) and Permian igneous association (296–285 Ma). One intrusion in this study (Mount Darcy; ca 375 Ma) pre-dates the KIA and is attributed to older Pama magmatism. Whole-rock geochemistry shows that most samples from the Permian group are characterised by high Sr/Y and (La/Yb)N together with low Y and Yb, defining a consistent adakitic affinity, whereas the Carboniferous group lacks these signatures. Petrogenetic constraints exclude low-silica adakite, magma mixing and slab-melt models, and instead favour partial melting of lower continental crust under garnet ± amphibole-stable conditions. This melting may have been related to crustal thickening and/or delamination during Carboniferous–Permian convergence along the Gondwana margin. Permian adakitic intrusions temporally overlap recognised mineralisation corridors in the Georgetown region. Although whole-rock fertility proxies alone are not diagnostic, the timing and geochemical character identify Permian magmatism as a priority target for evaluating potential genetic links to Cu–Au mineralisation using independent mineralisation and alteration constraints. KEY POINTS Zircon U–Pb ages define Permian and Carboniferous magmatic pulses in northeast Queensland. Permian intrusions show adakitic affinity: high Sr/Y and (La/Yb)N and low Y–Yb and petrogenetic constraints favour lower-crustal melting over slab-derived adakite. Permian adakitic magmatism reflects deep crustal processes on the Gondwana margin. Permian granodiorites overlap mineralised corridors, indicating Cu–Au fertility.