Petrogenesis of the Hoy lava field, a long-lived continental mafic volcanic province in eastern Australia

Small-scale continental basaltic fields can erupt with little warning and bring deep undegassed magmas to the surface rapidly. To explore the lifetime, petrogenesis and plumbing system architecture feeding such basaltic lava fields and compare them with large-scale shield volcanoes, we have focused on the Hoy lava field, central Queensland, Australia. Ar-40/Ar-39 geochronology, elemental and isotopic whole-rock geochemistry and mineral chemistry on selected Hoy samples reveal long-lived volcanism of ca 50 Ma and magma storage at mantle depths, notably different from the comparatively short duration (3-5 Myr) and crustal magma storage depths of shield volcanoes. In this study, four Hoy lava-field eruptive intervals spanning ca 50 Ma were investigated: 67.5 & PLUSMN; 0.3 Ma, 32.3 & PLUSMN; 0.6-31.6 & PLUSMN; 0.7 Ma, 21.9 & PLUSMN; 0.5 Ma and 18.1 & PLUSMN; 0.3 Ma. In all four eruptive events, samples are porphyritic alkali basalts and trachybasalts (11.41-6.45 wt% MgO) with incompatible element concentrations and Sr-Nd-Pb isotope ratios dominantly derived from a metasomatised sub-continental lithospheric mantle (SCLM) source with an enriched mantle I (EMI) signature. Complex crystal populations show major- and trace-element variations reflecting fractional crystallisation, magma recharge, magma mixing and mantle xenocryst entrainment. Clinopyroxene-melt thermobarometry indicates magma storage in SCLM reservoirs at & SIM;30-47 km depths. The nearby larger but shorter-lived (3-5 Myr) Buckland central volcano has similar source compositions; however, magma storage is limited and concentrated in the crust, resulting in increased crustal contamination. The results suggest that basaltic centres of contrasting scale and longevity are linked to distinct magma production mechanisms, fluxes, ascent and differentiation.

Automated summary

Small-scale continental basaltic fields can erupt suddenly and bring deep undegassed magmas to the surface rapidly. In this study, the volcanic activity, magma origin, and plumbing system architecture of the Hoy lava field in central Queensland, Australia were investigated and compared with large-scale shield volcanoes. The results show that the volcanism in the Hoy lava field has a long duration of approximately 50 million years and magma storage in the mantle depths, which is different from the relatively short duration and crustal magma storage depths of shield volcanoes.