Pittari, AdrianClark, Morgan2026-09-202026-09-202026https://hdl.handle.net/10289/18669The Kaimai Rhyolite Dome Complex (KRDC) is an extinct rhyolite dome complex on the Waikato-Bay of Plenty border which forms a prominent feature at the southern end of the Kaimai Range. Published ⁴⁰Ar/³⁹Ar and U-Pb zircon ages place dome emplacement between approximately 2.87 and 2.2 Ma, placing the KRDC within the Tauranga Volcanic Centre (TgVC) spatially, temporally, and within the transitionary phase of subduction-related volcanism within the North Island from the Coromandel Volcanic Zone to the Taupo Volcanic Zone. It is contemporaneous with the Alexandra Volcanic Group and Okete Volcanics of the western North Island, the wider Minden Rhyolite Subgroup of the TgVC, and predates the ~2.1 Ma Waiteariki Supereruption of the Omanawa Caldera. Despite its prominence on the Tauranga skyline and regional significance the KRDC has never been the primary subject of a dedicated study. This study applies modern volcanological techniques to define the complex and its place within the TgVC, incorporating field mapping, LiDAR-derived geomorphological analysis, petrography, SEM-EDS, XRD, whole-rock major and trace element geochemical analysis (XRF and LA-ICP-MS), and zircon saturation thermometry. The KRDC is recognised in this study for the first time and its six discrete dome centres, Te Weraiti, Kaimai, Kakahu, Hiwiroa, the Eastern Dome, and the Southeastern Dome, all previously mapped as Minden Rhyolite Group on Rotorua QMAP with undefined internal unit contacts and margins. Hiwiroa, the Eastern Dome, and the Southeastern Dome are recognised for the first time on the basis of geomorphology and morphometric analysis. The complex forms a coalesced composite dome ridge spanning 25.8 km along a N-S corridor with a total post erosional volume of 5.67 km3. Field and geomorphological evidence confirm that dome emplacement predates the Waiteariki supereruption. A three-tier framework was developed describing the structural control on emplacement of the dome centres derived from elongation ratios and spatial context, fault-controlled fissure emplacement (Te Weraiti, Kakahu; ER 2.81–3.16), intermediate point-source emplacement within a fault corridor (Kaimai; ER 1.44), and minimal direct fault control (Hiwiroa, Eastern, Southeastern; ER 1.47–1.85). The bimodal distribution of elongation ratios indicating two distinct emplacement modes of both fissure derived and point source rather than a continuous spectrum. Phenocryst assemblages at Te Weraiti and Kaimai are plagioclase + quartz ± biotite ± sanidine ± pyroxene. The KRDC lavas are hornblende absent distinguishing it from the hornblende bearing Waiteariki Ignimbrite. Devitrification groundmass textures are pervasive across all KRDC lavas displaying large spherulites of cristobalite + sanidine, an assemblage consistent across CVZ–TgVC Minden Rhyolites from ~7.8 Ma (Hahei) to ~2.2 Ma (KRDC). KRDC lavas are high-silica 74–78 wt.% SiO₂ high-K calc-alkaline to shoshonitic, peraluminous rhyolites that underwent plagioclase-dominated fractionation. Single-stage fractional crystallisation modelling could not produce these lavas from either Waiteariki Ignimbrite or the potential parental basaltic-andesite basement, requiring assimilation-fractional crystallisation. Zircon saturation thermometry produces mean KRDC melt temperatures ~40 °C cooler than the comparable Mount Misery rhyolite series within the TgVC, indicating the KRDC lavas represent a cooler, more evolved magma batch through a similar petrogenetic process but from a separate plumbing system.enAll items in Research Commons are provided for private study and research purposes and are protected by copyright with all rights reserved unless otherwise indicated.Tauranga Volcanic CentreCoromandel Volcanic ZoneTaupō Volcanic ZoneKaimai RangeKaimaiVolcanic DomeRhyolite DomeDome ComplexVolcanic geomorphologyStructural control on volcanismSpherulitesDevitrificationdome emplacementcristobaliteWaiteariki IgnimbriteTe WeraitiMinden Rhyolite SubgroupOmanawa CalderaNew Zealand VolcanismThesis