A review of the theory and evolution of fO2 cells is given. Particular attention is paid to the double cell design of Sato (1971). The incorporation of a servo mechanism after Sato (1971) is discussed. Calibration procedures for the entire system are presented with some emphasis on the use of nickel-neckel oxide and synthetic magnetite. The petrology of the Bushveld is reviewed in light of a possible fO2 hypothesis for the Critical Zone. Results of an examination of the E-F contact, Critical Zone, Eastern Bushveld, show a last equilibration at 1075 C and at a log10 fO2 value of -12.20. Two explanations are suggested for this intersection point: 1. It is the solidus, fO2 and temperature of the Bushveld magma at this horizon. 2. It is the post-cumulus, i.e., sub-solidus, fO2 and temperature of equilibration for the Bushveld rocks at the F-horizon. The first explanation is favored by the author and is being pursued currently. The second explanation requires ferrous/ferric equilibration but not chemical equilibration. This phenomenon is discussed from the consideration of diffusion rates for various ions. / Earth and Environmental Science

A relationship between the sulphur valence of a melt and f 02 has been determined. The relationship has been used to determine the f O2 conditions under which melt inclusions were trapped in andesitic magmas before magma mixing, and of a slowly cooled pyroclastic flow in which Fe-Ti oxide phases have re-equilibrated. The results help distinguish two trends in lavas from Lascar Volcano: In one, the melt fO2 is buffered by iron redox ratio, while in the other f02 is buffered by S02-H2S in a comagmatic vapour phase. The behaviour of sulphur was experimentally investigated in hydrous phonolitic and rhyolitic melt at 930 °C and 0.5 to 4 kbar. Pyrrhotite is stable under reducing conditions in both melts, and immiscible FeS sulphide liquid is stable under certain conditions of pressure and f S2 at 5 log units above the Ni-NiO buffer. Anhydrite and Srich sodalite are the usual magmatic S-bearing phase under oxidising conditions in rhyolitic and phonolitic melts respectfully. Melt sulphur content is positively correlated with f 02 and f S2. pressure has no significant effect for the conditions investigated. A thermodynamic model has been derived that successfully reproduces the results of this study and of a previous study. The partitioning of sulphur between vapour and melt is a function of f 02, f SZ, phase stabilities and mass balance constraints. Sulphur solubilities and f02 were determined for a suite of back arc basin basalts (BABB). The BABB samples follow two trends: those with low values of f02 have high S contents, whereas more oxidised samples have lower sulphur contents. The solubility behaviour can be described by sulphide-sulphate melt-vapour equilibria. The f02 of the oxidised samples implies that subducted material was incorporated into their magmatic source, a hypothesis supported by major and trace element studies of the samples

The Mont Saint-Hilaire alkaline complex, Québec, is a Cretaceous rift-related intrusion comprising two gabbroic suites and the East Hill suite, an assemblage of several distinct nepheline syenites and evolved syenitic rocks. Whole-rock analysis of the East Hill suite reveals two fractionation trends, one which is described by the syenitic lithologies and one by the evolved syenites and syenoids. A lamprophyric unit stands on its own, geochemically, consistent with typical lamprophyre petrogenesis. Whole-rock geochemistry of the East Hill suite shows moderate silica content but highly alkaline rocks, enriched in Mn, Zn, Zr, Y, and Ce. Chlorine and sulfur are important and present in abundant secondary sodalite and pervasive microsulfides. Mineral geochemistry indicates decreasing oxygen fugacity with cooling, and phases such as titanite (present) and aenigmatite (absent) defined boundaries in fO2 – T space. Oxygen fugacity data combined with petrography and geothermometry defined an 2 fO – T curve for the East Hill suite magma, revealing that the oxygen fugacity ranged between approximately 10-10 bar at intrusion down to 10-25 bar subsolidus, and that, owing to non-linearity of oxygen buffers, the 2 fO – T path crossed below QFM early, went above QFM late in the crystallization history and then above HM with cooling. A similar procedure applied to sulfur fugacity generated a trend of initial increase from about 10-4 to 10-2 bar followed by decreasing sulfur fugacity with cooling down to approximately 10-8 bar. The oxygen trend implies that earlier suggestions that oxidation of iron drove the evolution of pyroxenes towards aegirine are incorrect. Textural evidence of abundant alteration and secondary mineralization suggests subsolidus action of alkaline fluids. Contrary to previous studies, most sodalite in the East Hill suite is not primary but is the product of reaction of nepheline with chloride-rich fluids after crystallization. Sodalite pseudomorphs continued to react with these fluids, whose chemistry changed with time to silica- then carbonate-rich, resulting in further reactions that led to natrolite and dawsonite deposition, accompanied by late-stage rhodochrosite. It is hypothesized that the silica- and carbonate-rich phase of these fluids caused the decomposition of a melilite groundmass in the lamprophyre to a natrolite-calcite assemblage.

Thesis advisor: Ethan F. Baxter / Subduction zones are the primary areas of chemical and mass transfer between the Earth’s surface and the mantle. Dehydration during subduction has been linked to subduction seismicity, arc volcanism, and redox (fO2) changes in the subducting slab and overlying mantle wedge. Despite this, no petrologic record tracing the source of oxidizing fluids from the down going slab has yet been observed. To address this, this study shows a direct record of progressive redox change recorded in zoned garnet crystals from Sifnos and Syros, Greece that grew through the breakdown of the hydrous mineral lawsonite during subduction. Oxygen fugacities (fO2) calculated using garnet-epidote oxybarometry for multiple growth zones within single garnet grains have been compared with stable iron isotope compositions in the same growth zone. These combined measurements reveal that garnet cores grew under oxidized conditions, recording higher fO2 and lower 56Fe values, whereas garnet rims grew under more reduced conditions with lower fO2 and higher 56Fe values. This is consistent with the release of oxidizing fluids into the sub-arc mantle accompanying lawsonite breakdown and dehydration, leaving behind a progressively reduced residual slab mineral assemblage. These coupled fO2 and Fe isotope data show that slab dehydration accompanying lawsonite breakdown plays an important and measureable role in the global redox budget, and provides a mechanism for sub-arc mantle oxidation. / Thesis (MS) — Boston College, 2018. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

The objective of this thesis is to calibrate two oxygen barometers for kimberlite magmas in the system CaO-MgO-Al2O3-SiO2-TiO2-FeO based on the Fe and V content of monticellite, CaMgSiO4, that may be utilized in cases where oxides in olivine phenocrysts and perovskite are absent from a kimberlite pipe. I first calibrate a new oxygen barometer for kimberlite magmas based on the Fe content of monticellite in equilibrium with kimberlite liquids in experiments at 100kPa from 1230 to 1350C and at fO2 from NNO-4.1 to NNO+5.3 (where NNO is the nickel-nickel oxide buffer). The XFeMtc/XFeliq (where XFeMtc/XFeliq is the ratio of mole fraction of total Fe in monticellite and Fe in liquid) decreases with increasing fO2, consistent with only Fe2+ entering the monticellite structure. Although the XFe in monticellite varies with temperature and bulk composition, these dependencies are small (0.03) compared to that with fO2. The experimental data were fitted by weigted least square regression to the following relationship: DNNO= (log (0.858(0.021)*XFeliq/XFeMtc-1)-0.139(0.022))/0.193(0.004) (uncertainties at 2 sigma). I apply this oxygen barometer to natural kimberlite assuming the bulk rock FeO is that of their liquid FeO. Monticellite compositions of five kimberlites from both literature and my own investigations revealed a range in fO2 from NNO-3.5 to NNO+1.7. I finally use my well-defined monticellite-liquid Kd Fe2+-Mg to derive a range of Mg/(Mg+Fe2+) (Mg number) for kimberlite melts of 0.40-0.90. This range in composition is broader than previous estimates of 'primary' kimberlites, reflecting the diverse mantle sources and processes that occur during generation and ascent of kimberlites. Second, I calibrate a new oxygen barometer for kimberlite magmas based on the V content of monticellite in equilibrium with kimberlite liquids doped with 0.5 wt% V2O5 at 100kPa at 1280 and 1350C and at fO2 from NNO-4.1 to NNO_0.5. The DV Mtc/liq (DV Mtc/liq = V (ppm) in monticellite/V (ppm) in liquid) decreases with increasing fO2. The partitioning data can be fitted to a model consistent with V5+ as the dominant species in the melt phase above NNO whereas V4+ dominates below those conditions in kimberlitic magmas. The total DV Mtc/liq, which embodies both DV3+ Mtc/liq and DV4+ Mtc/liq, shows a very slight temperature and bulk composition dependence. The experimental data can be fitted by weighted least square regression to the following relationship: DNNO= (log(0.354(1.785)*Vliq/VMtc-1)-1.172(2.302))/0.111(0.071) (uncertainties at 2 sigma and V in ppm). In order to apply this oxygen barometer rigorously, the V concentrations of the kimberlite melt coexisting with monticellite need to be constrained. In contrast to the Fe-in-monticellite oxygen barometer for which the concentration of Fe in monticellite was close to that of the whole rock composition, the concentration of V in the bulk rock composition reflects mostly the large accumulation of olivine xenocrysts which contain low V concentrations. For that reason, the V-in-monticellite oxygen barometer cannot be applied to natural kimberlites until we find a way to overcome this problem. The vanadium concentrations of kimberlite melts are likely higher than the V concentrations of the whole rock compositions leading to underestimated fO2 values. / Graduate

Cities are sources of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), to surrounding regions and beyond. A spatially resolved, (5×5 km2), dynamic contaminant fate model named Spatially Oriented or SO-MUM was developed by coupling the fugacity based Multimedia Urban Model (MUM) (Diamond et al., 2001; Diamond et al., 2010c) and the Boundary Layer Forecast Model and Air Pollution Prediction System (BLFMAPS) which was developed at Environment Canada (Daggupaty et al., 2006). MUM was updated to contain a revised surface film sub-model which takes into account the dynamic nature of surface films. SO-MUM was illustrated by application to the City of Toronto, Canada. Spatially resolved air emissions of Σ88PCB were estimated to be ~230 (40-480) kg y-1, 280 (50-580) g y-1 km-2, and 90 (16-190) mg y-1 capita-1 and Σ26PBDE were estimated to be 28 (6-63) kg y-1, 34 (7-77) g y-1 km-2 and 11 (2-25) mg y-1 capita-1. These emissions were back-calculated from measured air concentrations and spatial chemical mass inventories yielding emission rates per mass inventory of 0.4 (0.05-1.6) and 0.1 (0.01-0.7) g kg-1inventory y-1, for Σ88PCBs and Σ26PBDEs, respectively. Approximately 30% and 16% of PCB and PBDE emissions emanate from the city’s downtown. Air advection accounted for ~95% (PCB) and ~70% (PBDE) of total air emission losses with the remaining balance depositing to the city. The metric “Urban Travel Distance” or UTD was introduced for quantifying the extent of an urban plume resulting from spatially heterogeneous emissions. For PCBs and PBDEs the UTDs were ~25 and ~30 km. The updated surface film sub-model indicated that films “bounce” higher vapor pressure semi-volatile organic compounds (SVOCs) back into the air but they act as a transient sink from air for lower vapor pressure SVOCs, thereby facilitating transport to surface waters. Model calculations suggest that if the PCB inventory is reduced, volatilization from near-shore Lake Ontario will become a net source of PCBs to air, but that neither near-shore Lake Ontario nor soil would become a significant volatilization PBDE source to air.

Cities are sources of persistent organic pollutants (POPs), such as polychlorinated biphenyls (PCBs) and polybrominated diphenyl ethers (PBDEs), to surrounding regions and beyond. A spatially resolved, (5×5 km2), dynamic contaminant fate model named Spatially Oriented or SO-MUM was developed by coupling the fugacity based Multimedia Urban Model (MUM) (Diamond et al., 2001; Diamond et al., 2010c) and the Boundary Layer Forecast Model and Air Pollution Prediction System (BLFMAPS) which was developed at Environment Canada (Daggupaty et al., 2006). MUM was updated to contain a revised surface film sub-model which takes into account the dynamic nature of surface films. SO-MUM was illustrated by application to the City of Toronto, Canada. Spatially resolved air emissions of Σ88PCB were estimated to be ~230 (40-480) kg y-1, 280 (50-580) g y-1 km-2, and 90 (16-190) mg y-1 capita-1 and Σ26PBDE were estimated to be 28 (6-63) kg y-1, 34 (7-77) g y-1 km-2 and 11 (2-25) mg y-1 capita-1. These emissions were back-calculated from measured air concentrations and spatial chemical mass inventories yielding emission rates per mass inventory of 0.4 (0.05-1.6) and 0.1 (0.01-0.7) g kg-1inventory y-1, for Σ88PCBs and Σ26PBDEs, respectively. Approximately 30% and 16% of PCB and PBDE emissions emanate from the city’s downtown. Air advection accounted for ~95% (PCB) and ~70% (PBDE) of total air emission losses with the remaining balance depositing to the city. The metric “Urban Travel Distance” or UTD was introduced for quantifying the extent of an urban plume resulting from spatially heterogeneous emissions. For PCBs and PBDEs the UTDs were ~25 and ~30 km. The updated surface film sub-model indicated that films “bounce” higher vapor pressure semi-volatile organic compounds (SVOCs) back into the air but they act as a transient sink from air for lower vapor pressure SVOCs, thereby facilitating transport to surface waters. Model calculations suggest that if the PCB inventory is reduced, volatilization from near-shore Lake Ontario will become a net source of PCBs to air, but that neither near-shore Lake Ontario nor soil would become a significant volatilization PBDE source to air.

In order to estimate the oxygen fugacity of Hawaiian lavas I have measured the ferric/ferrous ratios of samples from the 1984 eruption of Mauna Loa volcano and from the ongoing (1983-2017) Puu Oo eruption of Kilauea volcano. Fifteen samples were studied from the 21 day Mauna Loa eruption and 86 samples, erupted between 1983 and 2004, of the 34 year long Kilauea eruption. Both studies show that, in order to obtain reliable estimates of oxygen fugacity when, where, and how basaltic lava is sampled is of critical importance. Water-quenched lavas and spatter sampled at, or near vents, are less oxidized than water-quenched samples taken from open flow channels several kilometers away from the vent, or from slowly-cooled solidified flows. Additionally, samples of water-quenched lava traveling in lava tubes are less prone to oxidation than lava flowing in open channels, with oxygen fugacities similar to those of near vent quenched samples. The oxidation state of the rapidly quenched near vent or lava tube samples is at or below magnetite-wüstite (MW). This contrasts with the oxidation state of previously reported values for Hawaiian lavas, which are closer to fayalite-magnetite-quartz (FMQ) or nickel-nickel oxide (NNO). From this I conclude that the initial oxygen fugacity of Hawaiian parental magmas is close to MW and not FMQ, and that previous estimates of the oxidation state of Hawaiian magmas, based on data from solidified lava flows, were too high. This implies that the plume source of both Mauna Loa and Kilauea magmas is also close to MW, but not as reduced as the mantle source of mid-ocean ridge basalts.

No description available.

Kimberlitos são rochas vulcânicas que, frequentemente, contêm diamante, grafite e/ou carbonato, sendo a presença destes componentes diretamente influenciada pela variabilidade da fugacidade de oxigênio (fO2) do magma durante a sua ascenção. Segundo Chakhmouradian and Mitchell (2000), CaTiO3-perovskitas podem ser usadas para revelar as condições de alguns dos múltiplos estágios de cristalização da história magmática destas rochas. No intuito de estabelecer a fugacidade de oxigênio de magmas kimberlíticos naturais, CaTiO3-perovskitas foram cristalizadas experimentalmente em equilíbrio com um líquido kimberlítico sintético em altas temperaturas e diferentes condições de pressão e de fugacidade de oxigênio. Os experimentos mostraram que a perovskita incorporou maiores quantidades de Fe3+ com o aumento da fO2. A equação do oxigênio barômetro desenvolvida neste estudo pode ser aplicada em rochas kimberlíticas de diferentes condições de fO2, que contêm CaTiO3-perovskita e olivina. Na presente pesquisa, nós aplicamos este oxigênio barômetro em amostras do kimberlito Rosário do Sul, que é um kimberlito transicional localizado no limite sudoeste da Bacia do Paraná. Os dados de minerais deste kimberlito sugerem que sua fonte é um produto da reação de um líquido silicático-carbonatítico com o manto. Idades U-Pb de ~ 128Ma em CaTiO3-perovskitas (Conceição et al., in prep.) revelam que o kimberlito Rosário do Sul provavelmente entrou em erupção logo após o vulcanismo da Província Paraná-Etendeka. Temperaturas de cristalização, pressões e fO2 dos kimberlitos Rosário do Sul e Alfeu-I, outro importante kimberlito situado no sul do Brasil, foram calculadas. As condições de suas fontes foram estimadas usando diferentes métodos a partir das composições de olivinas, espinélios, CaTiO3-perovskitas, granadas, ortopiroxênios e clinopiroxênios. As temperaturas, pressões e condições de fO2 dos kimberlitos Rosário do Sul e Alfeu-I sugerem que eles foram transportados para a superfície em condições nas quais fluidos ricos em CO2 podem reagir com o manto silicático e produzir carbonatos. A composição mineral e as condições de formação do kimberlito Rosário do Sul indicam que a sua fonte pode ter sido metassomatizada por fluidos provenientes da reciclagem de uma placa oceânica subductada durante a quebra do Gondwana e abertura do Atlântico Sul, logo depois do vulcanismo da Província Paraná-Etendeka. As condições de formação dos kimberlitos Rosário do Sul e Alfeu-I são usadas também para estimar o potencial destes kimberlitos em preservar diamantes. / Kimberlites are volcanic rocks which often contain diamonds, graphite and/or carbonate, and the stability of these minerals is directly influenced by the variability of oxygen fugacity (fO2) of the magma during its ascent. Second Chakhmouradian and Mitchell (2000), CaTiO3-perovskites may be used to unravel the conditions of some of the multiple stages of crystallization in the magmatic history of these rocks. In order to establish oxygen fugacities of natural kimberlititic magmas, we experimentally equilibrated CaTiO3-perovskites with synthetic kimberlitic melts at high temperatures, different oxygen fugacities and different pressures. The experiments show that perovskite incorporates increasing amounts of Fe3+ with increasing fO2. The oxygen barometer equation developed in this study can be applied in kimberlite rocks that contain CaTiO3-perovskite and olivine from different fO2 conditions. In the present research, we applied this oxygen barometer in the Rosário do Sul kimberlite samples, which is a transitional kimberlite located in the southwestern edge of the Paraná Basin. The mineral data of this kimberlite suggest that its source is a product of the reaction of a silicate-carbonate liquid in the mantle. U-Pb ages of ~ 128 Ma on CaTiO3-perovskites (Conceição et al., in prep.) reveal that the Rosário do Sul kimberlite probably erupted just after the volcanism of Paraná-Etendeka Province. We calculated crystallization temperatures, pressures and oxygen fugacities (fO2) of Rosário do Sul and Alfeu-I kimberlites, another important kimberlite situated in the South of Brazil. Their source conditions are estimated using different methods from olivines, spinels, CaTiO3-perovskites, garnets, orthopyroxenes and clinopyroxenes compositions. The calculated temperature, pressure and fO2 values of Rosário do Sul and Alfeu-I kimberlites suggest that they were transported to the surface under fO2 conditions in which CO2-rich fluids may react with mantle silicates to produce carbonates. The mineral composition and fO2 conditions of Rosário do Sul kimberlite indicate that its source may have been metasomatized by fluids generated from the recycling of a subducted oceanic plate during the Gondwana breakup and the South Atlantic opening, just after the Paraná-Etendeka Province volcanism. The source conditions of Rosário do Sul and Alfeu-I kimberlites are also used to estimate the potential of these kimberlites to preserve diamonds.