Dissertations / Theses on the topic 'Volcanic geochemisty'
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1
Maund, J. G. "The volcanic geology, petrology and geochemistry of Caldeira volcano, Graciosa, Azores, and its bearing on contemporaneous felsic-mafic oceanic island volcanism." Thesis, University of Reading, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.370121.
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Miskovic, Aleksandar. "The connection between volcanism and plutonism in the Sifton Range volcanic complex, Northern Canadian Cordillera /." Thesis, McGill University, 2004. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=81363.
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The early Tertiary marked a period of intense magmatic activity in the Canadian Cordillera as a consequence of tectonic restructuring within the Kula-North American plate system from orthogonal to oblique convergence. Resultant calc-alkaline volcanism formed a discontinuous belt (Challis Arc) along the eastern margin of the Coast Plutonic Complex (CPC) from south-eastern Alaska through Yukon into west-central British Columbia and northern Washington State. The Sifton Range volcanic complex (SRVC) is the Yukon's largest Paleogene erosional remnant of volcanic rocks (240 km2), and represents the only coeval volcanic-plutonic suite within the Sloko-Skukum Group of southern Yukon Territory and northern British Columbia. It comprises a 900-m thick, shallow-dipping, volcanic succession dominated by intermediate to evolved lavas and abundant felsic pyroclastics deposited in a north-westerly trending half-graben. Three volcano-stratigraphic units are documented: (1) Lower Interbedded Unit, (2) Middle lavas, and (3) Upper Interbedded Unit. Locally, the volcanic sequence is intruded by biotite, hornblende, two-feldspar granites of the CPC's Nisling plutonic suite dated at 57.5 Ma. Felsite sills radiate from the main intrusive body, and together with numerous basaltic to dacitic dykes traverse the entire volcanic package. (Abstract shortened by UMI.)
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Ilanko, Tehnuka. "Geochemistry of gas emissions from Erebus volcano, Antarctica : an adventure in time, space, and volcanic degassing." Thesis, University of Cambridge, 2015. https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.709228.
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Ukstins, Peate Ingrid Anne. "Volcanostratigraphy, geochronology and geochemistry of silicic volcanism in the Afro-Arabian flood volcanic province (Yemen and Ethiopia)." Thesis, Royal Holloway, University of London, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.411244.
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Ritchie, Alistair B. H. "Volcanic geology and geochemistry of Waiotapu Ignimbrite, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geological Sciences, 1996. http://hdl.handle.net/10092/6588.
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Waiotapu Ignimbrite (0.710 ± 0.06 Ma) is a predominantly densely welded, purple-grey coloured, pumice rich lenticulite, which is exposed on both eastern and western flanks of Taupo Volcanic Zone. The unit is uniform in terms of lithology and mineralogy over its entire extent and has been deposited as a single flow unit. The unit contains abundant pumice clasts which are often highly attenuated (aspect ratios of c.1 :30) and are evenly distributed throughout the deposit. Lithic fragments are rare, never exceeding 1% of total rock volume at an outcrop and no proximal facies, such as lithic lag breccias, have been identified.
The deposit is densely welded to the base and only in more distal exposure does the ignimbrite become partially welded at the top of the deposit. Post-depositional devitrification is pervasive throughout the deposit, often destroying original vitroclastic texture in the matrix. Vapour phase alteration is extensive in welded and partially welded facies of the deposit.
Pumices within Waiotapu Ignimbrite appear to have been derived from two distinct magma batches, with differing Rb concentrations, that originated along different fractionation trends. Type-A pumices have significantly lower Rb than the subordinate type-B pumices. The presence of the pumices may represent the simultaneous evisceration of two spatially discrete magma chambers or the type-B chamber may have been intruded into type-A body, the magmas subsequently mingling prior to, or during, the eruption.
The source of Waiotapu Ignimbrite is poorly constrained, largely owing to the lack of meaningful maximum lithic data, and poor exposure of the unit. The distribution of the ignimbrite suggests that it was erupted from within Kapenga volcanic centre. If so the most proximal exposures of Waiotapu Ignimbrite are approximately 10km from the vent. Intensive and voluminous silicic volcanism, beginning with the eruption of the 0.33 Ma Whakamaru Group Ignimbrite eruptions, and extensive faulting within Kapenga volcanic centre will have obscured any intra-caldera Waiotapu Ignimbrite. The mechanism of eruption suggests that the source may not have been a caldera in the strictest sense, but instead a series of near linear fissures aligned with the trend of regional faulting.
Waiotapu Ignimbrite was generated in one sustained eruption and produced an energetic and high temperature pyroclastic flow. The lack of any recognised preceding plinian deposit, coupled with the energetic nature and paucity of lithics suggests eruption by an unusual mechanism. The eruption most likely resulted from the large scale collapse of a caldera block into the underlying chamber resulting in high discharge rates, which were no conducive to the development of a convecting column, and minimal vent erosion, resulting in negligible entrainment of lithics.
The density of welding and recrystallisation textures suggest that the flow retained heat to considerable distances which allowed the ignimbrite to weld densely to the base. The deposit was most likely progressively aggraded from the base, with material being supplied from an overriding particulate flow.
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James, Doreen Elizabeth. "The geochemistry of feldspar-free volcanic rocks." Thesis, Open University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.295080.
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Nyland, Roseanne E. "Evidence for early-phase explosive basaltic volcanism at Mt. Morning from glass-rich sediments in the ANDRILL AND-2A core and possible response to glacial cyclicity." Bowling Green State University / OhioLINK, 2011. http://rave.ohiolink.edu/etdc/view?acc_num=bgsu1308530267.
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Rice-Birchall, B. "Petrology and geochemistry of basic volcanics." Thesis, Keele University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.314570.
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Maussen, Katharine. "Carbon dioxide transport through Taal volcano’s hydrothermal system and Main Crater Lake (Philippines)." Doctoral thesis, Universite Libre de Bruxelles, 2018. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/271649.
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The presence of a hydrothermal system at Taal volcano is evident from the presence of a craterlake (Main Crater Lake, MCL), a caldera lake (Lake Taal) and several hot springs on the flanksof Taal volcano island and in the crater. Taal MCL, covering an area of 1.2 km², is acidic (pH= 3), warm (T = 30-33 °C) and its composition is dominated by Cl, Na and SO4. This thesisaims at understanding the geochemistry of Taal volcano’s hydrothermal system and the wayCO2 is transported through the hydrothermal system and MCL towards the atmosphere.The long-term geochemical evolution of MCL indicates that the hydrothermal system is madeof two reservoirs, one being volcanic and one geothermal in origin. The geothermal componentin Taal MCL has stayed rather constant since 1991, while the volcanic component hasdecreased.The low pH makes Taal volcano the perfect natural laboratory to study the behaviour of CO2,because there is no dissociation of CO2. A combined approach of total CO2 flux measurementsvia accumulation chamber and gaseous CO2 flux measurements via echo sounder shows thatmore than 90% of the total CO2 output of Taal volcano is due to the influx of dissolved CO2,migrating from the hydrothermal system to MCL via thermal springs under the lake surface.After verification of both horizontal and vertical homogeneity of dissolved CO2 concentrations,a continuous monitoring station was installed in 2013, measuring dissolved CO2 using aninfrared gas analyser protected by an ePTFE membrane, as well as several meteorological andenvironmental parameters. Several environmental and lacustrine processes influence CO2transport in MCL, including stratification, solar heating and rainfall.Taal volcano regularly goes through periods of unrest, characterised by seismic swarms,ground deformation and increased carbon dioxide flux. In 1991-1994, this was accompaniedby geochemical changes in MCL, including pH decrease and F, Si and Fe concentrationincrease. These changes can be attributed to an intrusion of magma to shallow levels less thanone kilometre deep. More recent unrests do not show these geochemical changes and are likelycaused by pressure changes in the hydrothermal system. The permanent monitoring stationrecorded hourly data on the 2015 unrest and showed that abnormally high CO2 concentrationswere recorded before the start of seismic or deformation activity, which makes continuous CO2monitoring a very valuable addition to current monitoring activities at Taal volcano.La présence d’un système hydrothermal au volcan Taal se manifeste par la présence d’un lac de cratère (Main Crater Lake, MLC) ainsi qu’un lac de caldera (Lake Taal) et de multiples sources d’eau chaudes sur les flancs et dans le cratère. Le MCL, avec une surface de 1.2 km², est acide (pH = 3), chaud (T = 30-33 °C) et composé principalement de Cl, Na et SO4. Le but de cette thèse est de comprendre la géochimie du système hydrothermal du Taal et la manière dont le CO2 est transporté à travers de celui-ci ainsi qu’à travers le MCL vers l’atmosphère. L’évolution géochimique à long terme indique que le système hydrothermal est composé de deux réservoirs, un d’origine volcanique et un autre d’origine géothermale. Le composant géothermal est resté plutôt constant depuis 1991, tandis que le composant volcanique a diminué. Le pH plutôt bas fait que le volcan Taal est le laboratoire naturel parfait pour étudier le comportement du CO2, parce qu’il n’y a pas de dissociation de CO2. Une approche combinée du flux de CO2 total via chambre d’accumulation, et flux de CO2 gazeux via echo sondeur montre que plus que 90% du flux de CO2 total est dû au CO2 dissout, qui migre depuis le système hydrothermal au MCL via des sources thermales sous la surface du lac. Après vérification de l’homogénéité horizontale et verticale du CO2 dissout, une station de monitoring en continu a été installée en 2013. Cette station mesure le CO2 dissout à l’aide d’un analyseur de gaz infrarouge protégé par une membrane en ePTFE, ainsi que de multiples paramètres météorologiques et environnementaux. Le transport de CO2 dans le MCL est influencé par plusieurs processus environnementaux et lacustre, comprenant la stratification, l’échauffement solaire et la pluie. Le volcan Taal connait régulièrement des périodes de crises caractérisées par une activité sismique, par une déformation du sol et par un flux élevé du CO2. En 1991-1994, ceux-ci ont été accompagnés par des changements géochimiques du MCL, comprenant une diminution du pH et une augmentation de la concentration de F, Si et Fe. Ces changements peuvent être attribués à une intrusion superficielle de magma à moins d’un kilomètre de profondeur. Les crises plus récentes ne montrent pas ces changements en géochimie et sont probablement causés par des changements de pression dans le système hydrothermal. La station de monitoring en continu a enregistré des données toutes les heures pendant la crise en 2015 et a montré que des concentrations particulièrement élevées en CO2 dissout ont été enregistrées avant le début de l’activité sismique et de déformation. Ceci a montré que le monitoring en continu du CO2 est une addition très précieuse aux activités de monitoring du volcan Taal.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished
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Dempsey, Scott Robert. "Geochemistry of volcanic rocks from the Sunda Arc." Thesis, Durham University, 2013. http://etheses.dur.ac.uk/6948/.
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Geochemical analyses of igneous rocks can provide valuable information about processes, element fluxes, and rock lithologies not evident at the surface. This is particularly important in subduction zone settings where complex interactions between the subducting plate, mantle wedge and arc crust cannot yet be measured by alternative methods. The Sunda arc, in SE Asia, provides an ideal opportunity to study the effects of subduction in a complex tectonic setting where the basement is poorly exposed and understood. However, in order to do so, magma compositions modified during differentiation in the arc crust must be effectively distinguished from those modified at the source. This study includes a detailed major- and trace element and isotopic (Sr-Nd-Hf-Pb) examination of volcanoes from west Java (Papandayan, Patuha and Galunggung), Central Java (Sumbing), east Java (Kelut) and Bali (Agung), the result of which provides greater insights into petrogenesis both across and along the arc. Contamination in the arc crust is more extensive than previously recognised, particularly in west and central Java where few volcanoes can be used in order to identify subduction and source contributions. In west Java, volcanoes such as Papandayan and Patuha show significant enrichments in isotope ratios above mantle values (e.g. 87Sr/86Sr ~ 0.706, 143Nd/144Nd ~ 0.5125, 208Pb/204Pb ~ 18.91 and 176Hf/177Hf ~ 0.2827) which indicates a terrigneous crustal contaminant. At Sumbing volcano, most magma compositions are similar to those at Merapi and Merbabu, and show strong evidence for the assimilation of carbonate-rich lithologies with some magmas becoming enriched in CaO, Sr and 87Sr/86Sr. Differentiation in volcanoes from east Java and the western part of the Lesser Sunda Islands (Bali, Lombok and Sumbawa) is dominantly controlled by fractional crystallisation, which provides better controls on source compositions. At Kelut, one group of samples show the most ‘depleted’ magma compositions yet discovered on Java, which contain MORB-like values for 143Nd/144Nd and 176Hf/177Hf (0.5130 and 0.2831 respectively). These samples represent the depleted (asthenospheric) mantle and are situated towards the front of the arc in east Java. It is likely that the progressive enrichment further back on the arc (i.e. Leucititic compositions at Ringgit-Besar) include more of an enriched (lithospheric) mantle (SCLM) component derived from the NW margin of Australia during the breakup of Gondwana.
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Malarkey, Jacqueline. "Micro-geochemistry of the mantle and its volcanic rocks." Thesis, Durham University, 2010. http://etheses.dur.ac.uk/131/.
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This thesis comprises three studies which utilise detailed micro-sampling techniques to understand the effects of melt infiltration in the continental lithosphere and the relationship of deeply derived kimberlite melts to lithospheric processes. To be able to make these links it is necessary to better constrain the geochemical composition of the primary kimberlite melt. • The first study investigates inter-grain trace element and Sr isotope variation in clinopyroxene (cpx), amphibole and melt from two spinel lherzolite xenoliths from the Middle Atlas Mountains, Morocco. These results support a multi-stage metasomatic process in which cpx and amphibole are recent additions to the lithospheric mantle, most recently equilibrated with a carbonatite melt. The limited Sr isotope variation in the cpx from this study is typical of global off-craton cpx implying that the majority of cpx in off-craton settings may have a recent, metasomatic origin. • The second micro-sampling study examines inter-grain trace element and Sr isotope variation in garnet and cpx in garnet lherzolite xenoliths within cratonic peridotites from Bultfontein, South Africa, and Pyramidfels, Greenland. The Sr isotope and trace element variation, combined with a lack of trace element equilibrium between cpx and garnet, imply that the majority of cpx is a recent addition, associated with the host kimberlite-type magma, whereas the garnet is added by an older event, probably by a melt related to either Group II kimberlite or lamproite. A global database of Sr and Nd isotope data for cpx and garnet indicates that these conclusions can be applied more widely. The metasomatic addition of cpx and garnet is limited to vein-wallrock reactions and therefore the majority of lithospheric mantle is concluded to be depleted harzburgite or dunite. • The third micro-sampling study focuses on constraining the primary geochemical characteristics of kimberlite magma by analysing the constituent phases (perovskite, olivine, apatite, phlogopite, calcite) for trace element and Sr isotope ratios from a sample of hypabyssal kimberlite from Jos, Somerset Island, Canada. An analogue study was carried out on an olivine melilitite from Saltpetre Kop, South Africa with a similar mineral suite (with the addition of melilite). These results show that phenocrystal olivine and apatite provide the best record of the source Sr isotope composition whereas perovskite, typically analysed by laser ablation, is more variable and influenced by crustal interaction, albeit to a limited extent. The results indicate that previously recorded differences between the Sr isotope compositions of whole rock kimberlites and the low-Cr megacryst suite, used to rule out a genetic relationship between the two, can be ascribed to later stage crustal interaction with the kimberlite. As a result, the link between kimberlites and the formation of the low-Cr megacryst suite is strengthened.
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Frisch, Joel A. "Geochemistry, Weathering and Diagenesis of the Bermuda Paleosols:." Thesis, Boston College, 2020. http://hdl.handle.net/2345/bc-ir:108780.
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Thesis advisor: Rudolph HonPleistocene-age terra rossa paleosols are situated on and are intercalated with eolianite and marine carbonate units across the Bermuda Islands. These clay-rich soils were originally thought to the derived from weathering of the volcanic seamount and/or from dissolution of the carbonate units, the paleosols are now believed to be primarily the result of atmospheric dust deposition from Saharan North Africa and the Sahel via long range transport, with some local inputs. If so, these soil units are mixtures of atmospheric deposition during one or more glacial- interglacial cycles. Previous investigations have been conducted on the paleosols to determine their provenance, age, and to identify unique characteristics for island wide mapping. We conducted comprehensive geochemical analyses to determine the degree of chemical weathering and diagenesis, and to identify processes responsible for their formation and development. The paleosols were found to be geochemically similar across all ages, and to show an increased degree of alteration with age rather than with their duration of subaerial exposure, indicating diagenesis by infiltrating meteoric waters as well subaerial weathering. Evidence of paleosol diagenesis suggests vadose flow across the island may not be limited to preferential pathways and that while flow through the limestones is complex, infiltrating waters appear to have allowed for additional alteration of the soils. In addition to the paleosols, clay-rich deposits with paleosol-like textures were identified during coring operations in Harrington Sound and Hungry Bay, beneath present-day sea level. The source and development histories of these materials were previously unknown. Since these clay deposits are situated beneath present-day sea level it is likely that they were deposited and chemically weathered exclusively during glacial low-sea level climate conditions. Geochemical analyses were conducted on the submarine clay samples to determine if they were related to the above-sea level paleosol and to identify their sources. Major and trace element signatures showed the submarine clay deposits to be chemically similar to the paleosols and to be derived from a similar upper continental crust-like parent. Trace element fingerprinting showed the samples to be derived from a parent similar to that of the paleosols; primarily atmospheric dust with some volcanic contributions. These findings provide additional evidence that trade wind vectors for dust transport were present during Pleistocene glacial climate conditions. Weathering indicators reveal the submarine clay samples to be somewhat less weathered than paleosols of similar age and comparable periods of exposure. Like the paleosols, the submarine clays underwent an initial period of rapid subaerial weathering which suggests warm humid climate conditions during glacial low sea level periods. However, the submarine clays did not experience extended periods of diagenesis, which may explain the somewhat lower degree of weathering. Evidence of inputs from the volcanic platform to the paleosols was limited, but comparisons with shallow volcanic rock and highly weathered volcanic residual known as the Primary Red Clay showed some similarities, suggesting that in-situ chemical weathering of the volcanic platform could produce a laterite with some characteristics similar to the Bermuda paleosols. Geochemical analysis of volcanic sands collected at Whalebone Bay showed the igneous fragments to be a result of mechanical weathering and sorting of heavy refractory minerals and we interpret these sediments to be best described as a beach placer deposit. These materials are enriched in insoluble trace elements and REE, and their contribution to the paleosols is limited
Thesis (MS) — Boston College, 2020
Submitted to: Boston College. Graduate School of Arts and Sciences
Discipline: Earth and Environmental Sciences
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Badger, Robert L. "Geochemistry and petrogenesis of the Catoctin Volcanic Province, central Appalachians." Diss., This resource online, 1989. http://scholar.lib.vt.edu/theses/available/etd-03042009-041139/.
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Woodhead, J. D. "Geochemistry of volcanic rocks from the Northern Mariana islands, West Pacific." Thesis, University of Oxford, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.379957.
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Berkelhammer, Samuel Ethan. "Initiation of the Wrangell arc: a record of tectonic changes in an arc-transform junction revealed by new geochemistry and geochronology of the ~29–18 Ma Sonya Creek volcanic field, Alaska." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/36236.
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Master of ScienceDepartment of Geology
Matthew E. Brueseke
The Sonya Creek volcanic field (SCVF) contains the oldest in situ magmatic products in the ~29 Ma–modern Wrangell arc (WA) in south-central Alaska. The WA is located within a transition zone between Aleutian subduction to the west and dextral strike-slip tectonics along the Queen Charlotte-Fairweather and Denali-Duke River fault systems to the east. WA magmatism is due to the shallow subduction (11–16°) of the Yakutat microplate. New ⁴⁰Ar/³⁹Ar and U-Pb geochronology of bedrock and modern river sediments shows that SCVF magmatism occurred from ~29–18 Ma. Volcanic units are divided based on field mapping, physical characteristics, geochronology, and new major and trace element geochemistry. A dacite dome yields a ~29 Ma ⁴⁰Ar/³⁹Ar age and was followed by eruptions of basaltic-andesite to dacite lavas and domes (~28–23 Ma Rocker Creek lavas and domes) that record hydrous, subduction-related, calc-alkaline magmatism with an apparent adakite-like component. This was followed by a westward shift to continued subduction-related magmatism without the adakite-like component (e.g., mantle wedge melting), represented by ~23–21 Ma basaltic-andesite to dacite domes and associated diorites (“intermediate domes”). These eruptions were followed by a westward shift in volcanism to anhydrous, transitional, basaltic-andesite to rhyolite lavas of the ~23–18 Ma Sonya Creek shield volcano (Cabin Creek lavas), including a rhyolite ignimbrite unit (~19 Ma Flat Top tuff), recording the influence of local intra-arc extension. The end of SCVF activity was marked by a southward shift in volcanism back to hydrous calc-alkaline lavas at ~22–19 Ma (Young Creek rocks and Border Lavas). SCVF geochemical types are very similar to those from the <5 WA, and no alkaline lavas that characterize the ~18–10 Ma Yukon WA are present. Sr-Nd-Pb-Hf radiogenic isotope data suggest the SCVF data were generated by contamination of a depleted mantle wedge by ~0.2–4% subducted terrigenous sediment, agreeing with geologic evidence from many places along the southern Alaskan margin. Our combined dataset reveals geochemical and spatial transitions through the lifetime of the SCVF, which record changing tectonic processes during the early evolution of the WA. The earliest SCVF phases suggest the initiation of Yakutat microplate subduction. Early SCVF igneous rocks are also chemically similar to hypabyssal intrusive rocks of similar ages that crop out to the west; together these ~29–20 Ma rocks imply that WA initiation occurred over a <100 km belt, ~50–60 km inboard from the modern WA and current loci of arc magmatism that extends from Mt. Drum to Mt. Churchill.
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Charland, Anne. "Stratigraphy, geochemistry and petrogenesis of the itcha volcanic complex, central British Columbia." Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=28433.
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The Itcha Volcanic Complex (IVC) is the easternmost shield of a series of bimodal central volcanic complexes which comprise the Anahim Volcanic Belt (AVB) in central British Columbia. The IVC lavas are distinctly bimodal, with a compositional gap between 52 and 58 wt% SiO$ sb2$ comprising late basaltic and hawaiitic lavas and early felsic lavas of Si-undersaturated to Si-oversaturated character. The hawaiite lavas dominate the late capping stage of the IVC. Their high Sr/Zr ratios indicate that they were derived by crystal fractionation of a clinopyroxene-dominated assemblage at high pressures ($ sim$10 kbar) from parental magmas with compositions similar to the most primitive alkali olivine basalts in the IVC. The majority of later evolved basalts have low Sr/Zr ratios indicating they formed by crystal fractionation at lower pressures.The similarity of isotopic and the incompatible element ratios suggests that the felsic and mafic magmas of the IVC are co-genetic. The early basal trachytes were derived by an AFC process in crustal magma chambers and appear to have assimilated a significant (15-20%) crustal component. Later, more evolved felsic lavas exhibit a wider range of Si-saturation, which appears to require parental basaltic magmas with a range of silica saturations with less, and more selective, crustal contamination. The compositional gap between the mafic and the felsic lavas of the Itcha shield appears to be related to the difficulty of erupting crystal-rich viscous lavas of intermediate composition. Viscosity models indicate that the rise in viscosity with decreasing Mg is slower at high pressures, which would favour the eruption of lavas of more evolved composition.
Late balsanites have distinct Nb/Zr and isotopic signatures (low $ rm sp{87}Sr/ sp{86}$Sr), requiring a mantle source distinct from that of the alkali olivine basalts.
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Christenson, Bruce William. "Fluid-mineral equilibria in the Kawerau hydrothermal system, Taupo Volcanic Zone, New Zealand." Thesis, University of Auckland, 1987. http://wwwlib.umi.com/dissertations/fullcit/8904865.
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The Kawerau hydrothermal system lies at the northern end of the Taupo Volcanic Zone, on the some 20 km south of the Bay of Plenty. The system, which is thought to have been active for at least 200,000 years, is situated over an area which has been volcanically active through time. Relatively recent local magmatism is found in the 800 m high, 3000-10,000 year old Mt. Edgecumbe dacite massif and the 200 m high Onepu Dome complex which lie adjacent to and within, respectively, the present day resistivity anomaly. Shallow reservoir fluids show evidence of steam heating as expressed by elevated bicarbonate and/or sulphate contents and mildly to strongly acidic pH, whereas the deep fluids are dominantly alkaline at their respective temperatures. The calculated base fluid composition is comprised of 2.5 wt% CO$/sb2$ and ca. 890 mg/kg Cl at 310$/sp/circ$C. Fluid inclusion studies show a largely stable, boiling point thermal regime through time, whereas oxygen stable isotope studies on hydrothermal carbonates prove the existence of one or more pulses of isotopically heavy fluids into the reservoir at some time(s) in the past. Hydrothermal alteration associated with these isotopic anomalies indicate strongly oxidising conditions relative to both alteration elsewhere in the reservoir and the present day reservoir redox conditions. Collectively, the data suggest a magmatic source for these transient, isotopically heavy fluids. The present day system is ore forming, as evident from both metal rich scales formed in the production silencers of the geothermal wells and open fracture reservoir mineralogy. Stockwork environments in the deep reservoir are host to both base and precious metals, and evidence indicates that boiling is the main depositional mechanism for these ore phases.Subscription resource available via Digital Dissertations only.
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Beresford, Stephen Willis. "Volcanology and geochemistry of the Kaingaroa Ignimbrite, Taupo Volcanic Zone, New Zealand." Thesis, University of Canterbury. Geological Sciences, 1997. http://hdl.handle.net/10092/5738.
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The 0.23 Ma Kaingaroa Ignimbrite is a composite multiple flow-unit ignimbrite erupted from Reporoa Caldera, Taupo Volcanic Zone (TVZ), New Zealand.
The Kaingaroa Ignimbrite has a complex internal stratigraphy with a complex basal tephra sequence of intercalated fall, surge and flow deposits, and three ignimbrite units, with strikingly proximal to medial facies variation. Proximal facies deposits are dominated by coarse lithic breccias up to 45m thick which are interpreted as co-ignimbrite lag breccias. These lag breccias are-some of the thickest so far documented. Welding and thickness variations in the extensive Old Waiotapu Rd (OWR; kg1) and Webb ignimbrite unit (WIU; kg2) suggests gradual thickening away from source, interpreted to represent ponding in a shallow alluvial lowland or basin.
A detailed lithic componentry study indicates changes in lithic diversity and abundance between stratigraphic units which mark changes in vent conditions, increasing depth of lithic provenance and hence inferred fragmentation level. Lithic fragments reveal aspects of the sub-caldera geology, which is dominated by an andesitic volcano with leuco-gabbroic subvolcanic roots, intercalated welded ignimbrites, rare low-grade metasedimentary basement and meta-rhyolites. Gabbros and meta-rhyolites suggest complex metasomatic and fumarolic processes adjacent to the Kaingaroa magma system. The presence of tourmaline-bearing meta-rhyolites and meta-ignimbrites and tourmalinite is the first documented occurrence of tourmaline and tourmalinite in TVZ.
Four pumice types are defined on pumice chemistry and mineralogy. These pumices are interpreted to represent samples of a weakly continuously zoned magma chamber (70-75% SiO2), which was progressively tapped during the eruption. Trace element and rare earth element systematics are consistent with an origin of type A magma from a type D parent by minor fractionation of plagioclase, zircon, and trace contents of Fe/Ti oxides and orthopyroxene. An additional hornblende-, 2-pyroxene-phyric dacite pumice/bleb (69% SiO2) was sampled from the Tokiaminga sub-unit, but is mineralogically and compositionally different from Kaingaroa pumices. Post-caldera rhyolites are
mineralogically and chemically variable, with broad similarities to Kaingaroa pumices. The Kaingaroa magma components show reverse isotopic zonation i.e. decreasing 87Sr/86Sr and increasing 143Nd/144Nd with differentiation, suggesting syn-eruptive mingling and evisceration of the multiple magma batches occurred during the climactic caldera collapse phase.
The Kaingaroa Ignimbrite has been mis-correlated by previous workers with the Matahina, Mamaku, and Rangatira Point ignimbrites, and three new units described in this thesis; Kawerau ignimbrite, Wheao sheet, and the welded ignimbrite of Wairakei drill holes. It is clear that ignimbrite correlation is difficult in TVZ because of the poor exposure and the limited stratigraphic sections that document multiple units. The Kawerau ignimbrite remains an enigma, largely because of the anomalously high Zr, Hf and Zn contents, suggestive of a relationship to 'alkaline' rhyolites, and the presence of unusual magnesium poor manganoan fayalite of vapour-phase origin. Identification of these units and other
intermediate size ignimbrite in the stratigraphic interval between Whakamaru-group, and Mamaku ignimbrites requires further careful documentation, but suggests a temporal clustering of ignimbrites sourced from throughout TVZ.
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Mathieson, N. A. "Geology, structure and geochemistry of the Ordovician volcanic succession in SW Cumbria." Thesis, University of Sheffield, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.378480.
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Wallis, Susan M. "Petrology and geochemistry of Upper Carboniferous-Lower Permian volcanic rocks in Scotland." Thesis, University of Edinburgh, 1989. http://hdl.handle.net/1842/13183.
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Gardeweg, Moyra C. "The geology, petrology and geochemistry of the Tumisa volcanic complex, north Chile." Thesis, Kingston University, 1991. http://eprints.kingston.ac.uk/20550/.
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Tumisa (5,658 m) is a Pleistocene composite volcano located in the western margin of the Upper Cenozoic volcanic chain of the CVZ in northern Chile. It consists of a ~ 25 km[sup]3 non-welded deposit of block-and-ash flow and small-volume ignimbrites, small flank domes and a double peak formed by two cones, the younger a composite of lava flows and domes. The lava flows, domes and blocks of the pyroclastic flows are coarse-grained, crystal-rich dacite (host lava) with dominant plagioclase (An[sub]30-50) and magnesio-hornblendes with different proportions of orthopyroxene (En[sub]62-68), biotite and quartz phenocryts. Accesory phases include Fe-Ti oxides and apatite. These mineral assemblage coexist in disequilibrium with Mg-olivine and Mg-orthopyroxene. In addition to disequilibrium textures and mineral assemblages, there are widespread fine-grained, dark mafic inclusions. The inclusions are interpreted as blobs of hot (> 1100°C) basic magma containing < 5% crystals (Mg-olivine, Mg-orthopyroxene, Cr-rich spinel), which quenched on intrusion into a cool (~ 770°C), wet dacitic magma in a shallow level chamber (4-14 km). Repetitive supplies of the basic magma from depth triggered eruptions in a slowly cooling magma chamber. Mingling and partial hybridization of compositionally distinct multiple end-members was the dominant evolutionary process, combined with limited fractional crystallization, mainly in the basic magma. Post-mixing crystallization produced strongly contrasting mineral compositions due to temperature and compositional gradients. Calcic plagioclase (An[sub]50-74) and low-SiO[sub]2/high-TiO[sub]2 hornblende crystallized as prismatic or acicular aggregates in the inclusions (hyalodoleritic textures), as thin reversely zoned rims on resorbed phenocrysts and as groundmass grains. Clinopyroxene formed as acicular crystals in the inclusions, groundmass grains in the dacites and as reaction coronas around quartz. Mechanical transfer of phenocrysts between the two magmas and partial hybridization shifted whole-rock compositions (58.9-66.2% SiO[sub]2 for the host lavas; 52.7-58.4% SiO[sub]2 for the inclusions). The compositions are typical of normal calc-alkaline volcanoes from the western margin in the Central Andes. Isotopic ratios ([sup]87 Sr/[sup]86 Sr: 0.7055-0.70683; [sup]143 Nd/ [sup]144 Nd: 0.51239 to 0.51255, [epsilon][sup]Nd: -2.1 to -4.8) are within the normal range for parental magmas in this region and reflect minimal interaction with crustal material.
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Wigley, Rochelle Anne. "The geochemistry of the Karoo igneous volcanic and intrusive rocks of Botswana." Master's thesis, University of Cape Town, 1995. http://hdl.handle.net/11427/21335.
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Bibliography: pages 183-191.The Mesozoic basalts and dolerites of Botswana underlie an estimated area of 150 000km2 and form part of the Karoo Igneous Province of southern Africa. The distribution of Karoo basalts in Botswana is limited essentially to three main sub-basins, the Central Kalahari Subbasin, northern Botswana and the Tuli Syncline and a major dyke swarm, with a WNW strike, extends across Botswana from the Namibian to Zimbabwean borders. This dissertation is a reconnaissance study which concentrates on the recognition and definition of distinct geocheinical sub-groups within the Karoo volcanic and intrusive rocks of · Botswana. 128 new whole rock samples were analyzed for major and trace element concentrations, in addition to the 70 whole rock analyses from Botswana which were available in the UCT database.· Mineral analyses and rare earth element compositions for selected samples are also presented. The basalts and dolerites of Botswana are assigned to one of the three geochemical lineages, i.e. the low-K20, the high-K20 and the felsite lineages on the basis of Si02, MgO and K20 concentrations. A number of distinct geochemical sub-groups· are recognised within these lineages according to whole rock compositions, normative mineralogy, petrography and outcrop character. The low-K20 lineage is subdivided into two main sub-groups on the basis of the Ti02 and Zr concentrations, i.e. the LTZ- and HTZ-type basalt and dolerite sub-groups. The LTZtype basalt sub-group (with ~2% Ti02 and ~250ppm Zr) represents the bulk of the Botswana dataset where the LTZ basalts of Botswana are shown to be lateral equivalents to the Lesotho Formation basalts of the Central Karoo area, considerably expanding the known outcrop area of this basalt type. Two dolerites are the only samples of intrusive equivalents of this voluminous LTZ basalt type in Botswana.,
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Onuonga, Isaac Oriechi. "Geochemistry and mineralization of Buru and Kuge volcanic carbonatite centres, Western Kenya." Thesis, University of St Andrews, 1997. http://hdl.handle.net/10023/15470.
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Western Kenya hosts a number of Tertiary and Quaternary alkaline volcanic carbonatite centres, such as Rangwa, the North and South Ruri centres, Kuge, Homa Mountain and Legetet which are located along an old Precambrian major shear zone lying within the Nyanza rift, off the main Kenyan (Gregory) rift. The centres consist of agglomerates and breccias with mixed clasts of silicate rocks and carbonatites, interbedded with carbonatitic and nephelinitic tuffs. The volcanic assemblage is transected by high level sheets and dykes of calcite carbonatite and ferrocarbonatite which were probably later feeders for the volcanic eruptions. Carbon, oxygen, and sulphur isotopic compositions were determined for calcite, siderite and barite from the Buru and Kuge carbonatite centres. Wide ranges in the isotopic compositions of the minerals were observed with values for delta13C and delta18O for the Buru calcites ranging from +1.27 to -3.23‰ (PDB) and +11.25 to +26.21‰ (SMOW). The delta13 C and delta18O for the Kuge calcites are -3.11 to -8.44‰ (PDB) and +18.09 to +25.73‰ (SMOW). The Buru siderites plot in a narrow and restricted range at -3.07 to -4.39‰ (PDB) and +12.61 to +16.10‰ (SMOW). Data on the sulphur isotopic composition from the Buru hill carbonatite show a fairly widespread variation in delta34S ranging from +4.50 to +12.40‰ (CDT), whereas Kuge hill displays a slightly more homogenous isotopic composition with values ranging from +1.10 to +5.10‰ (CDT). The carbon and oxygen isotopic compositions from the Buru and Kuge carbonatite centres do not retain the primary isotopic signatures expected for magmatic primary carbonatites. Most of the variations in isotopic composition have been attributed to secondary processes involving low temperature (60° to 144°C) hydrothemal alteration and isotopic exchange between the carbonatites and fluids (meteoric water). Higher delta18O values (+21.91 to +26.21‰) with a significant increase in delta13Cvalues (-1.48 to +1.27‰) shown by the most oxidized samples from the Buru carbonatite may indicate the involvement of supergene exchange with atmospheric CO2 at relatively lower temperatures (< 50°C). The variations in 34S shown by the two centres compared to mantle sulphur could be due to either redox processes and/or isotopic fractionations due to loss of volatiles. The Buru and Kuge carbonatite centres are characterized by enriched rare earth element (REE) values dominated by higher abundances of LREEs with steep chondrite-normalized distribution patterns. The lateritic zone at Buru hill, however, contains the greatest concentrations of REEs, barium, iron and manganese compared to the fresh carbonatite in which calcite and particularly siderite increase in abundance as the influence of supergene processes decrease with depth. The most common rare earth minerals encountered in the Buru and Kuge carbonatite centres are the fluorocarbonates (bastnaesite, synchysite and parisite), and monazite. The lanthanide fluorocarbonate and monazite control the concentration and bulk distribution of the REEs. The replacement textures of the lanthanide fluorocarbonates and monazite indicate that they are secondary in origin and appear to have been introduced by late stage, low temperature hydrothermal processes. The rare earth minerals are commonly accompanied by fluorite, and barite. Stable isotope studies suggest that the low temperature mineralogical changes and REE mineralization observed in western Kenyan carbonatites were controlled initially by hydrothermal activity and later by supergene processes. Higher delta18O and values, especially in the oxidized zones, correspond to higher REE abundances.
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Morter, Bethany Kathleen. "Understanding the history of a volcanic arc: linking geochemistry of Cenozoic volcanic cobbles from the Wrangell arc, Alaska, to upper plate and subducting slab tectonic processes." Thesis, Kansas State University, 2017. http://hdl.handle.net/2097/38164.
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Master of ScienceDepartment of Geology
Matthew E. Brueseke
The Wrangell arc (WA) is a ~29 Ma magmatic belt, extending from south-central Alaska into the Yukon Territory, that lies above the edges and leading front of the Yakutat microplate, a buoyant oceanic plateau that is causing shallow subduction (11-16º) in the region. The WA occurs in a transition zone between “normal” Aleutian subduction to the west and dextral strike-slip tectonics to the east, accomplished by the Totschunda, Denali, and Duke River faults. This geologic setting offers a chance to study the interrelations between subduction, strike-slip motion, and slab-edge magmatic processes in a relatively well-exposed arc. We implemented a novel technique of applying geochemical and geochronologic analyses on volcanic cobbles collected from glacio-fluvial systems (rivers, streams, and glaciers) encircling/draining the WA. Our primary objective is to integrate our cobble datasets with the existing bedrock and detrital sand records to develop a comprehensive understanding of WA magmatism through time and space. Our secondary objective is to test the validity of this novel technique for reproducing what is documented from bedrock samples and its potential for utilization in other locations. This study provides new major element data from 215 samples and trace element data from 236 samples collected from 17 major rivers that drain from the modern western and central WA (this study excludes the eastern WA). This study also provides new age data from a total of 119 samples from 10 major rivers. New geochronology of modern detrital volcanic cobbles and sand/zircons reveal that the WA initiated at ~29 Ma and that magmatism migrated northwestward through time. Cobble ages and locations across the arc agree with the northwestward progression of magmatism previously identified by Richter et al. (1990). Forty-seven cobbles are dated <~1 Ma and only nine cobbles are dated 29 – ~20 Ma, whereas there are no cobbles from 17 – ~13 Ma. Geochemical data reveal similarities between our data and that of the <~5 Ma WA defined by Preece and Hart (2004): Trend 1 (transitional-tholeiitic), Trend 2a (calc-alkaline), Trend 2b (calc-alkaline, adakite-like). Therefore, we use the geochemical framework defined in Preece and Hart (2004) to contextualize spatio-temporal trends of magmatism and tectonic implications in the WA during its ~29 m.y. history. Trend 2a and 2b cobbles are spatially and temporally ubiquitous in the WA, indicating that subduction and partial slab melting have been the dominant tectonic processes throughout WA history. Trend 1 cobbles are not found in southwestern WA rivers and are temporally restricted to ~11 – ~6 Ma and <1 Ma, suggesting intra-arc extension has occurred in discrete periods during WA history. These conclusions are confirmed by the existing (Richter et al., 1990; Skulski et al., 1991; 1992; Preece and Hart, 2004; Trop et al., 2012) and new (Berkelhammer, 2017; Weber et al., 2017) bedrock records. Finally, this study shows that the sampled cobble lithologies largely reproduce the known bedrock record in geochemical, temporal, and spatial contexts, which suggests the novel methodology applied here can be used in other locations where field conditions limit access to bedrock.
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Van, der Stelt Barry J. "The geochemistry, petrology and tectonic setting of the Truro Volcanics /." Title page, contents and abstract only, 1990. http://web4.library.adelaide.edu.au/theses/09SB/09sbv241.pdf.
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Soto, Emmanuel. "Identifying the Origins of Volcanic Ash Deposits Using Their Chemical and Physical Compositions." FIU Digital Commons, 2018. https://digitalcommons.fiu.edu/etd/3650.
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Recent ocean sediments collected offshore Chile by Ocean Drilling Program Leg 202 contained layers of volcanic ash of unknown origin. These deposits may have originated from sources in the Southern Volcanic Zone (SVZ) within the Andean Volcanic Belt to the east, or from explosive volcanoes in the southwestern Pacific transported by westerly prevailing winds. In this study, mineral and glass textures and compositions of Leg 202 ashes were evaluated to try to determine the sources of the ash layers. Ash fragments were imaged and analyzed for major elements using an SEM with X-Ray detector and for trace elements using LA-ICPMS. Results show that the ash samples are rhyolitic and that they formed in a subduction zone setting or a continental margin. The ash samples have distinct physical and geochemical features that can be used in the future to identify their source(s) by comparison to databases of Pleistocene Recent explosive volcanic eruptions.
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Njilah, Isaac Konfor. "Geochemistry and petrogenesis of tertiary-quaternary volcanic rocks from Oku-Ndu area, N.W. Cameroon." Thesis, University of Leeds, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.305536.
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Cosky, Brian Wright. "Os-Sr-Nd-Pb ISOTOPIC AND TRACE ELEMENT STUDY OF MAGMATIC PROCESSES WITHIN THE SIERRA DEL CHICHINAUTZIN VOLCANIC FIELD, TRANS-MEXICAN VOLCANIC BELT." Miami University / OhioLINK, 2010. http://rave.ohiolink.edu/etdc/view?acc_num=miami1291864089.
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Tebar, Henry J. "Petrology and geochemistry of volcanic rocks from the Pocdol Mountains, Bicol Arc (Philippines)." Thesis, University of Canterbury. Geology, 1988. http://hdl.handle.net/10092/9408.
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The Pocdol Mountains are part of the Bicol arc-- a SE-trending calcalkaline volcanic belt adjacent to the Philippine Trench. Recent volcano-stratigraphic studies and five new K-Ar ages have delineated seven lithostratigraphic units in the Pocdol Mountains. The rocks are grouped into : (i) a Western Pocdol Mountains (WPM) series, and (ii) an Eastern Pocdol Mountains (EPM) series. WPM eruptives comprise Early Pliocene basaltic tuff breccias and lavas (Malobago volcanics) and Middle to Late Pleistocene (0.478-0.065 Ma) andesitic lavas and tuff breccias (Lison and Kayabon volcanics). EPM volcanism produced (i) Middle Pliocene dacitic tuff breccias and minor lavas and the Matacla Dome (Suminandig volcanics). The stratified unit is intercalated with lenses of siltstones and sandstones (Rangas conglomerate), and was later (0.065 Ma) intruded by the Rangas microdiorite; (ii) Middle Pliocene to Early Pleistocene andesi tic tuff breccias, laharic breccias and lavas (Pangas volcanics), which were erupted mostly from four flank vents, with associated igneous intrusives (Pangas intrusives), and (iii) Late Pleistocene to Recent andesitic lavas, tuff breccias and lahars of the Cawayan volcanics (<0.04 Ma) and basaltic tephras and minor lavas of the Pulog volcanics (<0.03 Ma).
The rocks are plagioclase-phyric, with minor clino- and orthopyroxene, titanomagnetite and hornblende. Olivine is only found in the Malobago volcanics. Glomerophyric and pilotaxitic textures are common, and most phenocrysts show normal or oscillatory zonation. Disequilibrium features are rare. The inferred crystallisation sequence of WPM lavas is titanomagnetite-olivine-pyroxene-amphibole, accompanied by plagioclase. EPM rocks have the same order of crystallisation as WPM lavas, except that olivine was not involved. Overall mineralogy of the lavas suggests a low pressure (<9 kb) crystallisation and estimated equilibration temperatures from coexisting two pyroxenes range from 1006°C to 1135°C. The absence of ilmenite phases precludes an estimate of oxygen fugacity. WPM lavas comprise medium-K high-Al basalt to medium-K and high-K andesite, whereas the EPM rocks consist of low-K basaltic andesite to medium-K andesite and dacite. Major oxide and trace element variations indicate two possible parental liquids, each generating the WPM and EPM series; the EPM lavas also show two fractionation trends : a dacite and an andesite crystallisation paths. WPM lavas generally contain greater abundances of large-ion lithophile (LIL) and high field strength (HFS) ions, but they have lower concentrations of ferromagnesian elements. Low Mg/(Mg+Fe²), Ni and Cr values in both series suggest that the liquids are not in equilibrium with mantle peridotite.
Both WPM and EPM lavas are considered to have been derived by closed-system low pressure POAM fractionation (Gill, 1981) of a basaltic source, that may have been generated by higher degrees of partial melting within the mantle wedge and/or the subducted slab, together with some degree of enrichment from the downgoing slab. Stratigraphic criteria and least-squares mixing models indicate that by precipitating plagioclase, orthopyroxene, titanomagnetite and clinopyroxene, both Lison and Kayabon andesites (WPM series) were probably derived from a high-alumina basaltic source (Malobago volcanics), whereas the Suminandig, Pangas and Cawayan volcanics (EPM series) originate from a low-K basaltic andesite liquid (Pulog volcanics). However, if it is assumed that a dacitic melt was sitting on top of the EPM reservoir, then it is necessary to invoke liquid fractionation (McBirney et al., 1985), whereby the more fractionated liquids move upward and are collected at the roof of the chamber, due to density stratification in the magma reservoir.
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Sides, Isobel Ruth. "Volatile geochemistry and eruption dynamics at Kīlauea Volcano, Hawai'i." Thesis, University of Cambridge, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.608131.
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Grimmer, Stephen C. "Geochemistry and petrography of alkali volcanics from the Oslo Palaeorift Norway." Thesis, Keele University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.293779.
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McKee, Ryan A. "Structure and volcanic evolution of the northern Highland Range, Colorado River Extensional Corridor, Clark County, Nevada." Thesis, San Jose State University, 2017. http://pqdtopen.proquest.com/#viewpdf?dispub=10255048.
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A geologic map was drafted of the northern Highland Range (1:24,000 scale), rock units defined, and samples of the volcanic units were obtained and analyzed to produce a representative suite of chemical analyses to characterize the range of geochemical variability. The style, relative timing, and orientation of faults and dikes, and the magnitude and variability of stratal tilting was examined to evaluate the structural and magmatic evolution of the northern Highland Range in the context of models for the Colorado River Extensional Corridor and Black Mountains accommodation zone. Methods involved field mapping of the range scale structure and geometry of faulting, structural interpretation, and geochemical analysis of ten representative samples by X-ray spectrometry. Structural data was interpreted with stereonets; geochemical whole rock, and major elemental data was analyzed by comparing elemental oxides; trace elemental data was analyzed by normalizing to chondrite concentrations. The northern Highland Range is a ca. 3,000 m-thick sequence of volcanic and volcaniclastic flows and breccias overlain by regionally extensive tuffs (Mt. Davis and Bridge Spring). Unique mineralogy, geochemistry and lithologic character of some units and volcanic vent facies, as well as the presence of domes and dikes feeding the extrusives argue for local derivation from a dome/stratocone volcanic complex that was mostly restricted to the northern Highland Range.
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Mazza, Sarah Elizabeth. "Understanding Non-Plume Related Intraplate Volcanism." Diss., Virginia Tech, 2016. http://hdl.handle.net/10919/83554.
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Intraplate volcanism is a worldwide phenomenon producing volcanoes away from active plate boundaries, a process that cannot yet be sufficiently explained by plate tectonic processes, and thus is still a missing piece in the understanding of the dynamics and evolution of our planet. Models for the formation of intraplate volcanism are dominated by mantle plumes, but alternative explanations, such as adiabatic decompression triggered by lithospheric delamination, and edge driven convection (EDC), could be responsible for magmatism. This dissertation explores intraplate volcanic locations that do not fit the mantle plume model, and presents geochemical evidence for lithospheric delamination and edge driven convection for the cause of volcanism.
I studied an Eocene volcanic swarm exposed in the Appalachian Valley and Ridge Province of Virginia and West Virginia, which are the youngest known igneous rocks along the Eastern North American Margin (ENAM). These magmas provide the only window into the most recent deep processes contributing to the post-rift evolution of this margin. This study presents the first high precision 40Ar/39Ar ages along with new geochemical data, and radiogenic isotopes that constrain the melting conditions and the timing of emplacement. Modeling of the melting conditions suggests that melting occurred under conditions slightly higher than average mantle beneath mid-ocean ridges. Asthenosphere upwelling related to localized lithospheric delamination is a possible process that can explain the intraplate signature of these magmas that lack evidence of a thermal anomaly.
The Virginia-West Virginia region of the ENAM also preserves a second post-rift magmatic event in the Late Jurassic. By studying both the Late Jurassic and Eocene magmatic events we can better understand the post-rift evolution of passive margins. This study presents a comprehensive set of geochemical data that includes new 40Ar/39Ar ages, major and trace-element compositions, and analysis of radiogenic isotopes to further constrain their magmatic history. Modeling suggests that the felsic volcanics from both the Late Jurassic and Eocene events are consistent with fractional crystallization. Lithospheric delamination is the best hypothesis for magmatism in Virginia/West Virginia, due to tectonic instabilities that are remnant from the long-term evolution of this margin, resulting in a 'passive-aggressive' margin that records multiple magmatic events long after rifting ended.
Finally, Bermuda is an intraplate volcano that has been historically classified as mantle plume related but evidence to support the plume model is lacking. Instead, geophysics have argued that EDC is the best model to explain Bermuda volcanism. This study presents the first geochemical analysis of Bermuda volcanism, and found that Bermuda was built by two different magmatic processes: melting of carbonated peridotite to produce silica under-saturated, trace element enriched volcanics and melting of an enriched upper mantle component that produced silica saturated volcanics. We attribute the cyclicity of silica under-saturated and silica saturated volcanics to EDC melting.Ph. D.
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Jones, Christina. "Trace element fingerprinting in the Gulf of Mexico volcanic ash." Thesis, Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/863.
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Krcmarov, Robert. "The geology, petrology and geochemistry of the volcanic unit at Olympic Dam, South Australia /." Title page, contents and abstract only, 1987. http://web4.library.adelaide.edu.au/theses/09SB/09sbk91.pdf.
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Robison, Lori Carol 1955. "Geology and geochemistry of Proterozoic volcanic rocks bearing massive sulfide ore deposits, Bagdad, Arizona." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/558078.
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Matthews, Stephen John. "Volcanology, petrology and geochemistry of Lascar Volcano, northern Chile." Thesis, University College London (University of London), 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.283332.
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Cannatelli, Claudia. "Geochemistry of Melt Inclusions from the Fondo Riccio and Minopoli 1 Eruptions at Campi Flegrei (Italy)." Thesis, Virginia Tech, 2006. http://hdl.handle.net/10919/32993.
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Campi Flegrei is a large volcanic complex located west of the city of Naples, Italy. The area has been the site of volcanic activity for more than 60 ka and represents a potential volcanic hazard owing to the large local population. In this study, the geochemistry of the magma associated with two different eruptions at Campi Flegrei has been characterized, with the aim to identify geochemical trends that may help to predict the style and nature of future eruptions. Two eruptions of different age and eruptive style have been selected for study, Fondo Riccio (9.5 ka) and Minopoli 1 (11.1 ka). A scoria (CF-FR-C1) and a bomb (CF-FR-C2) were collected from the Fondo Riccio eruption, and two scoria samples were collected from Minopoli 1 (CF-Mi1-C1 and C2) eruption.
The pre-eruptive volatile content of magma plays an important role in the style of eruption and can be assessed from studies of melt inclusions (MI) contained in phenocrysts. Major and trace elements in Fondo Riccio MI show a wider variation compared to those in Minopoli 1 MI suggesting that the Fondo Riccio magma residence time was longer compared to the Minopoli 1 magma. Analyses of volatile contents in MI suggest that Fondo Riccio magma may have been more water-rich than Minopoli 1 magma, consistent with the more explosive character of this eruption compared to Minopoli 1. Trace element data suggest a combination of arc volcanic and upper continental crust magma as the source for the Fondo Riccio and Minopoli 1 eruptions.Master of Science
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Baker, Joel Allen. "Stratigraphy, chronology and geochemistry of cenozoc volcanism in Western Yemen." Thesis, Royal Holloway, University of London, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.299765.
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Koebli, Danielle. "A Geochemical and Petrological Analysis of the San Rafael Volcanic Field, Utah." Scholar Commons, 2017. https://scholarcommons.usf.edu/etd/7417.
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The San Rafael Volcanic Field, Utah, is a 4.6 Ma extinct monogenetic field that is found in the Northern Transition Zone of the Colorado Plateau. The field has been eroded, leaving the dikes, conduits, and sills visible. Within the sills we see evidences of immiscibility in the form of an intermediate syenite (~50 wt% SiO2) enclosed in a mafic shonkinite (~48 wt % SiO2). Field relations indicate that sills were formed due to single events (Richardson et al., 2015), which makes in-situ differentiation the process at the origin of both rock types. Geochemical data supports differentiation of syenite and shonkinite from a single melt. The syenites are more enriched in LREE than shonkinites. The rocks are enriched in LREE compared to an OIB source, indicating melting of a hydrated lithosphere interacting with an asthernospheric garnet peridotite. Olivine with a composition of Fo80-90 further support asthernospheric origin, and pyroxenes indicate that depth of crystallization would have begun around 33 Km, indicating that the melt would have pooled at the base of the crust as it traveled, supporting base of the lithosphere origins. Rhyolite-MELTS modeling further supports differentiation within the sills as the formations of feldspars, biotite and hornblende did not occur until ~800m which would have allowed for fractional crystallization to occur, leading to the immiscibility process and resulting formation of syenite and shonkinite.
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Lees, Katherine Roisin. "Magmatic and tectonic changes through time in the Neogene volcanic rocks of the Vale area, Oregon, north western USA." Thesis, Open University, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.261042.
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Hoal, Brian Garner. "Proterozoic crustal evolution of the Awasib Mountain terrain, southern Namibia, with speical reference to the volcanic Haiber flats formation." Doctoral thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/21889.
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Bibliography: pages 245-257.The middle to late Proterozoic Awasib Mountain terrain (AMT) straddles the boundary between the Rehoboth and Gordonia subprovinces in southern Namibia. The AMT is made up of two major crustal components, the older of which is correlated with the Namaqualand Metamorphic Complex (NMC), and the younger with the Sinclair Sequence.
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McHugh, Kelly C. "APPLICATIONS OF TRACE ELEMENT AND ISOTOPE GEOCHEMISTRY TO IGNEOUS PETROLOGY AND ENVIRONMENTAL FORENSICS." Miami University / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=miami1494441686890672.
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De, Joux Alexandra. "Cosmos greenstone terrane : insights into an Archaean volcanic arc, associated with komatiite-hosted nickel sulphide mineralisation, from U-Pb dating, volcanic stratigraphy and geochemistry." Thesis, University of Edinburgh, 2014. http://hdl.handle.net/1842/8918.
Full textAbstract:
The Neoarchaean Agnew-Wiluna greenstone belt (AWB) of the Kalgoorlie Terrane, within the Eastern Goldfields Superterrane (EGS) of the Yilgarn Craton, Western Australia, contains several world-class, komatiite-hosted, nickel-sulphide ore bodies. These are commonly associated with felsic volcanic successions, many of which are considered to have a tonalite-trondhjemite-dacite (TTD) affinity. The Cosmos greenstone sequence lies on the western edge of the AWB and this previously unstudied mineralised volcanic succession contrasts markedly in age, geochemistry, emplacement mechanisms and probable tectonic setting to that of the majority of the AWB and wider EGS. Detailed subsurface mapping has shown that the footwall to the Cosmos mineralised ultramafic sequence consists of an intricate succession of both fragmental and coherent extrusive lithologies, ranging from basaltic andesites through to rhyolites, plus later-formed felsic and basaltic intrusions. The occurrence of thick sequences of amygdaloidal intermediate lavas intercalated with extensive sequences of dacite lapilli tuff, coupled with the absence of marine sediments or hydrovolcanic products, indicates the succession was formed in a subaerial environment. Chemical composition of the non-ultramafic lithologies is typified by a high-K calc-alkaline to shoshonite signature, indicative of formation in a volcanic arc setting. Assimilation-fractional crystallisation modelling has shown that at least two compositionally distinct sources must be invoked to explain the observed basaltic andesite to rhyolite magma suite. High resolution U-Pb dating of several units within the succession underpins stratigraphic relationships established in the field and indicates that the emplacement of the Cosmos succession took place between ~2736 Ma and ~2653 Ma, making it significantly older and longer-lived than most other greenstone successions within the Kalgoorlie Terrane. Extrusive periodic volcanism spanned ~50 Myrs with three cycles of bimodal intermediate/felsic and ultramafic volcanism occurring between ~2736 Ma and ~2685 Ma. Periodic intrusive activity, related to the local granite plutonism, lasted for a further ~32 Myrs or until ~2653 Ma. The Cosmos succession either represents a separate, older terrane in its own right or it has an autochthonous relationship with the AWB but volcanism initiated much earlier in this region than currently considered. Dating of the Cosmos succession has demonstrated that high-resolution geochronology within individual greenstone successions can be achieved and provides more robust platforms for interpreting the evolution of ancient mineralised volcanic successions. The geochemical affinity of the Cosmos succession indicates a subduction zone was operating in the Kalgoorlie Terrane by ~2736 Ma, much earlier than considered in current regional geodynamic models. The Cosmos volcanic succession provides further evidence that plate tectonics was in operation during the Neoarchaean, contrary to some recently proposed tectonic models.
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Fan, Jianzhong. "Geochemistry and petrogenesis of unaltered and altered volcanic sequences in the southern Abitibi greenstone belt." Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1995. http://www.collectionscanada.ca/obj/s4/f2/dsk3/ftp04/nq23923.pdf.
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So, Chak-tong Anthony, and 蘇澤棠. "Petrology and geochemistry of volcanic rocks of the Lantau Peak Area, Lantau Island, Hong Kong." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31221646.
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Arslan, Mehmet. "Mineralogy, geochemistry, petrology and petrogenesis of the Meydan-Zilan (Ercis-Van, Turkey) area volcanic rocks." Thesis, University of Glasgow, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.437611.
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Grubensky, Michael J. "Structure, geochemistry, and volcanic history of mid-Tertiary rocks in the Kofa Region, southwestern Arizona." Thesis, The University of Arizona, 1987. http://hdl.handle.net/10150/558071.
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So, Chak-tong Anthony. "Petrology and geochemistry of volcanic rocks of the Lantau Peak Area, Lantau Island, Hong Kong /." Hong Kong : University of Hong Kong, 1999. http://sunzi.lib.hku.hk/hkuto/record.jsp?B21375549.
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Maurice, Charles 1976. "Archean mafic volcanism of the Eastern Ungava peninsula, Northern Quebec." Thesis, McGill University, 2001. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=31270.
Full textAbstract:
Mafic volcanic sequences of tholeiitic basalt and associated komatiite are common to many Precambrian shields of the world. Recently discovered remnants of Archean greenstone belts in the northern Superior Province of Canada exhibit characteristics similar to larger belts of the southern Superior Province. Three of the best preserved belts are trapped in ca. 2.77--2.88 Ga tonalitic intrusives of the Faribault-Thury amphibolitic Complex (FTC), and provide direct evidence for the nature of the mantle prior to the major volcanic events of the late Archean (ca. 2.7 Ga). These belts consist of amphibolite facies rocks of volcanic and sedimentary origin, in one of which a wide variety of cumulates are preserved. The association of the lavas with meta-pelites, iron formations, marbles, and the lack of conglomerate and clearly crustally contaminated lavas suggest that the FTC lavas were erupted in an oceanic environment. The three belts are separated by over 100 km, but exhibit similar chemical characteristics and may represent the base of an extensive early mafic crust. (Abstract shortened by UMI.)