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Item Volcanism and rapid sedimentation affect the benthic communities of Deception Island, Antarctica(Elsevier B.V., 2021-05-01) Angulo-Preckler C; Pernet P; García-Hernández C; Kereszturi G; Álvarez-Valero AM; Hopfenblatt J; Gómez-Ballesteros M; Otero XL; Caza J; Ruiz-Fernández J; Geyer A; Avila CDeception Island is amongst the most active volcanoes in the Southern Ocean, with over 20 explosive eruptions in the last ca. 200 years. The eruption that formed the caldera at Deception Island occurred 3980 ± 125 calendar years Before Present, and it is the largest eruptive event documented in Antarctica during Holocene. Since then, post-caldera volcanic activity has comprised many scattered eruptive vents across the island. Mortality of benthic organisms has been reported during the most recent eruptions occurred on the island, in 1967, 1969, and 1970 Common Era (CE), with very low abundances of organisms during the 1967–1973 CE period. Within the sea-flooded part of the caldera depression, named Port Foster, a submarine volcanic axis with several volcanic cones is observed. An interdisciplinary team sampled the best morphologically preserved volcanic edifice within Port Foster, the so-called Stanley Patch. Geophysical data traced the volcano and characterized its morphology and inner structure. Underwater scuba sampling allowed to acquire sediment and rock samples, photographs and video images of the benthic organisms and seascape. Morphology of Stanley Patch cone and textural characteristics of the collected pyroclastic rocks indicate that the volcanic edifice was originated during an explosive eruption. Furthermore, the lack of palagonitization, quenched pyroclast margins, and hyaloclastite deposits indicate that this cone has formed on-land, before the caldera floor became inundated by the seawater, highlighting the complex intra-caldera evolution of Deception Island. A sediment core from the crater was collected for sedimentological, and geochemical analysis. Antarctic climate and seasonal sea ice, together with organic degradation due to high sedimentation rates, explain the low total organic carbon data measured. The volcanic history of the island has probably avoided the development of a stable benthic community over time, similar to other Antarctic shallow communities. Moreover, the current geomorphological conditions still shape different benthic communities than in the surrounding coastal ecosystems. Stanley Patch, and the whole Port Foster, provide a natural laboratory for benchmarking the reestablishment of benthic communities on a volcanic-influenced shallow marine environment, offering relevant data for future studies evaluating global climate change effects on the Antarctic seabed.Item Spinel oxides as petrogenetic indicator minerals : providing a basis for ascent chronometry and geohygrometry using experimental petrology and high-precision in situ analysis : a dissertation submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Manawatū campus, New Zealand(Massey University, 2021) Coulthard Jr., Daniel A.The spinel-structured oxides are near-ubiquitously observed accessory phases in ultramafic-felsic igneous rocks. Their status as so-called “petrogenetic indicator” minerals reflects the sensitivity of their composition to changes in the thermodynamic state of magmatic systems. Analyses of their compositions has thus elucidated a wealth of insight into the states and evolution of magmatic systems in general. This thesis builds upon this foundation by illustrating that ionic diffusion within chromian spinel is also highly sensitive to oxygen fugacity. Using the results of internally heated pressure vessel experiments, I show that increasing oxygen fugacity is correlated with higher Fe³⁺ mobility within the spinel structure at the expense of Al over Cr, while Fe²⁺-Mg systematics follow established empirical relationships. Cr mobility remains slow under highly oxidizing conditions but is still expected to diffuse and approach an equilibrium composition over longer timescales. These observations can be utilized to infer ascent rates for chromite-bearing mafic igneous rocks. Using sparse mineral data from the Troodos Ophiolite, model results indicate that not only are chromites out of equilibrium with residual melts but that they were disequilibrated less than 200 years prior to eruption. Another potential use for spinel minerals is as sensitive geohygrometers. However, routine spectroscopic methods cannot be used for these minerals due to the effect that abundant Fe has on the detection limit of OH during analysis. Instead, ion microprobe methods were utilized and demonstrate that H detection is achievable for titanomagnetite. While chromian spinels do not appear to hold any H, titanomagnetites produced during IHPV experiments and those sourced from natural samples contain an intrinsic H signal intensity that indicates H is soluble to trace concentrations. These results suggest that titanomagnetite should be systematically studied through experimental methods in order to identify how H is incorporated. Thus, the “petrogenetic indicator” status of both chromian and Fe-rich spinel minerals may be expanded into the fields of diffusion chronometry and geohygrometry, respectively.Item Melt generation, storage and ascent below Tongariro Volcanic Complex, Southern Taupo Volcanic Zone : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Manawatu, New Zealand(Massey University, 2018) Arpa, Maria Carmencita B.The study of Tongariro Volcanic Complex in New Zealand gives an opportunity to view arc magmatism from a setting where the classic arc structure is overprinted by the regional tectonic setting. Instead of viewing the volcano (and associated magmatic processes) as a component of a volcanic arc to determine the origin of andesitic magmas, focus was given on magmatic processes within the volcanic complex. Processes within the plumbing system of the volcanic complex and their implications on andesitic magmatism and volcanic hazards were determined by tracking magma, of selected eruptive products, from their reservoirs to the surface. By focusing on processes that may determine the petrological characteristics of specific deposits (from known eruptions), the influence of local structures associated with eruptive centres within the complex and the diversity of resultant eruption styles may be interpreted as magmatic processes are evaluated. The deposits for this study are from the last 16 ka history of Tongariro, majority are from the last 10 ka. These are from known eruptions and the deposits were mapped, dated and studied by previous researchers. Lava flow eruptions are from Te Maari and Red Crater, and Plinian to vulcanian eruptions are represented by the Mangamate Tephra and Ngauruhoe deposits. For each eruptive deposit, whole rock major, trace and isotope compositions were determined. Groundmass and mineral components were analysed for major elements. Major element and volatile (H2O, CO2, S, Cl) compositions of melt inclusions in component olivine and pyroxene crystals were also determined. The deposits from the recent history of Tongariro Volcano can be related to a common source. The basalts can differentiate to more evolved andesitic to dacitic compositions by crystallization and/or melting. Magmatic differentiation takes place in different reservoirs, at different depths, within the complex. Differences were observed in the volatile contents of the magmas and these may be related to magma storage and ascent processes. Magmatic processes for the deposits in this study, interpreted from compositions, considered and are consistent with eruption styles.