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Accessory mineral thermometry and thermodynamic modelling are fundamental tools for constraining petrogenetic models of granite magmatism. U–Pb geochronology on zircon and monazite from S-type granites emplaced within a semi-continuous, whole-crust section in the Georgetown Inlier (GTI), NE Australia, indicates synchronous crystallisation at 1550 Ma. Zircon saturation temperature ( T  zr ) and titanium-in-zircon thermometry ( T  (Ti–zr) ) estimate magma temperatures of ~ 795 ± 41 °C ( T  zr ) and ~ 845 ± 46 °C ( T  (Ti-zr) ) in the deep crust, ~ 735 ± 30 °C ( T  zr ) and ~ 785 ± 30 °C ( T  (Ti-zr) ) in the middle crust, and ~ 796 ± 45 °C ( T  zr ) and ~ 850 ± 40 °C ( T  (Ti-zr) ) in the upper crust. The differing averages reflect ambient temperature conditions ( T  zr ) within the magma chamber, whereas the higher  T  (Ti-zr)  values represent peak conditions of hotter melt injections. Assuming thermal equilibrium through the crust and adiabatic ascent, shallower magmas contained 4 wt% H 2 O, whereas deeper melts contained 7 wt% H 2 O. Using these H 2 O contents, monazite saturation temperature ( T  mz ) estimates agree with  T  zr  values. Thermodynamic modelling indicates that plagioclase, garnet and biotite were restitic phases, and that compositional variation in the GTI suites resulted from entrainment of these minerals in silicic (74–76 wt% SiO 2 ) melts. At inferred emplacement  P–T  conditions of 5 kbar and 730 °C, additional H 2 O is required to produce sufficient melt with compositions similar to the GTI granites. Drier and hotter magmas required additional heat to raise adiabatically to upper-crustal levels. S-type granites are low- T  mushes of melt and residual phases that stall and equilibrate in the middle crust, suggesting that discussions on the unreliability of zircon-based thermometers should be modulated.

Reassessing zircon-monazite thermometry with thermodynamic modelling: insights from the Georgetown igneous complex, NE Australia