| Čoahkkáigeassu: | <p xmlns:etd="http://www.ouls.ox.ac.uk/ora/modsextensions">Cainozoic volcanism occurs in eastern Australia as a broad zone of discontinuous, small-volume, dominantly basaltic provinces. Central volcano provinces show a strong correlation between age and latitude, younging towards the south, hence the interpretation that they are related to a mantle hotspot. Previous work has interpreted the composition of lavas from these provinces using a fourcomponent model involving material from a mantle plume, the shallow asthenosphere, continental lithosphere together with AFC processes in the lower crust.</p><p xmlns:etd="http://www.ouls.ox.ac.uk/ora/modsextensions">The purpose of this thesis is to describe the petrology of the Buckland province, a relatively poorly-studied central volcano in central Queensland, and to constrain models for the petrogenesis of its lavas, assessing whether this is consistent with the four-component model outlined above. Mafic lava compositions show a wide range of silica saturation and degree of evolution. Highly undersaturated basanites are interpreted as being dominantly from the shallow asthenosphere, with the five most magnesian samples apparently containing a HIMU-like component. Comparison with experimental data demonstrates that the geochemistry of the most primitive basalts is consistent with decompressional melting within a plume whose T<sub>P</sub> lies in the range 1410-1500°C and which has an above-average Fe/Mg. Evolved mafic lavas show geochemical and petrographic evidence for polybaric assimilationfractional crystallisation in the crust. Megacrysts of plagioclase, orthopyroxene and clinopyroxene represent the extract assemblage from the lower crust (probably at pressures >10kbar, owing to the absence of olivine), while low-pressure crystallisation of olivine also took place. Both the elevation of the province (up to 1100m above sea level) and occurrence of high-pressure megacrysts are consistent with previous models of underplating at the crust-mantle boundary. Lavas from the neighbouring province of Springsure show greater evidence of AFC in the upper crust, while those from the northern part of the Mitchell province contain megacrysts of olivine which is suggestive of a slightly lower crystallisation pressure in the lower crust.</p>
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