Thesis (M.S.)--Oregon State University, 2007. / Printout. Includes bibliographical references (leaves 91-96). Also available on the World Wide Web.

Volcanic and magmatic processes are controlled by the composition of the magmas involved and the nature and structure of their underlying plumbing systems. To understand and predict volcanic behaviour, it is of critical importance to characterize the associated magmatic plumbing and supply system. This study investigates the magma plumbing system beneath Bali, Indonesia by employing several thermobarometric models using mineral phases in lavas from the simultaneous eruptions of Agung and Batur volcanoes in 1963 and the 1974 eruption of Batur. Compositional data were acquired from feldspar, pyroxene, and olivine crystals, using electron microprobe analysis, as well as from whole-rock samples using inductively coupled plasma mass spectrometry. Clinopyroxene-melt and clinopyroxene composition thermobarometers were then applied to equilibrated clinopyroxene-melt couples, while plagioclase-melt thermobarometry was employed on equilibrated plagioclase-melt pairs. The results were used to construct comprehensive magmatic plumbing models for Agung and Batur and are compared with geochemical, geophysical and petrological data on these volcanoes and others in the region. For the 1963 Agung eruption, results from clinopyroxene-melt thermobarometry suggest dominant crystallisation levels between 18 and 22 km depth. Clinopyroxene from the 1963 eruption of Batur record crystallisation depths between 12 and 18 km, whereas clinopyroxene from the 1974 Batur eruption show a main crystallisation level between 15 and 19 km. Furthermore, plagioclase-melt thermobarometry indicates the existence of shallow level magma reservoirs, with depths between 3 and 7 km for the 1963 eruption of Agung, between 2 and 4 km for the 1963 Batur eruption and between 3 and 5 km for the 1974 Batur event. The deep magma storage regions notably coincide with lithological boundaries in the crust and mantle beneath Bali, while the shallow reservoirs are consistent with recent geophysical studies that point to regional shallow-level magma storage. An along-arc comparison reveals this trend to be characteristic of Sunda arc magma storage systems and highlights the utility of a thermobarometric approach to detect multi-level systems beneath recently active volcanic systems.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1963. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 87-92).

A brief description of a low grade regionally metamorphosed region in the Madoc area in Southern Ontario is given. Plagioclase compositions from metamorphosed basic rocks of this region were studied with the intention of finding co-existing plagioclases in the region of peristerite solvus. X-ray diffraction was found useful in determining the presence of two co-existing plagioclase feldspars. Two peaks occurred in the region of the 131 and 131 peaks if this was the case. Compositional determinations for albitic feldspars were found inaccurate as the angular separation (Δ29) between the 131 and 131 peaks was apparently reduced indicating plagioclase composition less than An0. For anorthite rich feldspars the angular separation between 131 and 131 gave relatively accurate compositions. The electron microprobe was used·to determine the plagioclase compositions of samples from the Madoc area. Results compared well for anorthite rich feldspars determined by both X-ray diffraction and. electron microprobe techniques. Only one rock was found to contain two plgioclases related to a peristerite solvus. A zoned nature appears to exist. Albite and oligoclase coexist, the oligoclase grading into andesine. Also, albitic plagioclase is associated with epidote inclusions; a diffusion relationship probably existing between the two. With increased metamorphic grade, epidote disappears and the anorthite content of plagioclase increases. / Thesis / Bachelor of Science (BSc)

No description available.

Feldspar minerals are framework aluminosilicates that comprise approximately 60 percent of the Earth's crust. The elastic and thermodynamic properties of this important mineral group are needed for the interpretation of seismic wave velocities, for understanding cation partioning patterns and for the determination of phase boundaries and reactions involving feldspars in the Earth's crust. Until recently, no systematic approach has been applied to describe the structural behavior of feldspars as a function of pressure, temperature and composition. In this thesis, high-pressure and high-temperature X-ray diffraction data were collected for feldspars over a range of compositions which has led to the development a structural model that allows one to predict the structural evolution of feldspars at depth in the Earth's crust. Specifically, the equations of state have been determined for two plagioclase feldspars (An20 and An78) with different states of Al/Si ordering using single-crystal X-ray diffraction. This study has shown that the introduction of Al,Si disorder into plagioclase structures at constant composition softens the structure by 4(1)% for An0, 2.5(9)% for An20 and is essentially zero for An78 compositions. The effect of pressure on the structure of an ordered An20 was also determined up to 9.15 GPa using single-crystal X-ray diffraction and it was found that the dominant compression mechanism involves tilting of the AlO4 and SiO4 tetrahedra. Similarly, high-temperature single-crystal X-ray diffraction data collected from an ordered An26 plagioclase and powder X-ray diffraction collected on a suite of Na-rich plagioclases that were refined using the Rietveld method indicate that the major structural response to increased temperature involves tilting of the tetrahedra. Building on ideas originally proposed by Dr. Helen Megaw, the changes in the conformation of the tetrahedral framework of feldspars can be described in terms of four distinct tilt systems of rigid tetrahedra. This model demonstrates that the fundamental reason for the observed anisotropy and volume change of feldspars lies in the topology of the tetrahedral framework with the greatest contribution attributed to tilt systems 2 and 3. / Ph. D.

For each of 24 grains of low plagioclase with ‘Inferred An' contents 4.1, 6.8, 16.6, 27.7, 30.2, 35.8, 36.6, 37.6, 38.7, 43.1, 44.2, 48.0, 50.8, 51.9, 55.0, 56.5, 56.6, 57.9, 61.8, 62.1, 64.5, 76.8, 78.2, and 90.4 the following properties were measured: (1) y*, (2) location of the crystallographic axes, (3) separation of the non-Bragg e-diffractions from precession photographs, (4) refractive indices α, β, and γ, (5) the location of the optic axes, (6) the location of the principal vibration directions X, Y, and Z, (7) and a value of 2V. Plots of y* versus the product, αβγ, which correlates linearly to anorthite content, confirm the presence of two structural discontinuities in the low plagioclase series. The angular attitude of the two optic axes and of the principal vibration directions plotted stereographically relative to b* (at S = 0, E= 0) andc (at S = 90, E = 90) for each grain follow the classic migration curves of Reinhart (1931) with slight revision. The orientation of the principal vibration axes X, Y, and Z is related quantitatively to crystallographic directions b*, c, and A by means of Euler angles Φ, θ, and ψ introduced by Burri et al. (1967) and to the crystallographic axes a, b*, and C by a set of new Euler angles θ₁, θ₂, and θ₃. / Master of Science

Les processus d’anatéxie représentent la première étape dans la genèse des granites. La fusion partielle de la croûte inférieure peut produire des structures leucocrates à signatures chimiques particulières, très différentes. Par conséquent le lien qui existe entre certaines migmatites et les granites crûstaux peut être ambigu. Ce projet de thèse est une étude de l’évolution des processus d’anatexie au sein des métapelites de la formation de Bandelierkop dans le Zone Marginale Sud de la Ceinture du Limpopo en Afrique du Sud. Ce travail comprend une étude complête du métamorphisme, de la géochimie et de la géochronologie des paragneiss granulitiques de deux carrières dans la zone nord de la Zone Marginal Sud, la carrière de Bandelierkop et la carrière de Brakspruit, où la fusion partielle d’une croûte néoarchéenne peut être observée. Le projet a pour but de répondre à deux problématiques principales: (1) contraindre de manière précise les conditions et l’âge de l’épisode métamorphique de la Zone Marginale Sud, avec ce que cela implique pour la géodynamique archéenne, (2) comprendre les réactions de fusion partielle en absence de fluide et leur contrôle sur la chimie des migmatites et le liens qui existent entre les leucosomes, la source, le liquide de fusion et les granites de type S. Les informations P-T-t enregistrées dans les métapelites de la formation de Bandelierkop, contraintes par des diagrammes d’équilibre de phase ainsi que de la géochronologie sur zircon, donnent une idée sur les processus de différentiation crustale dans la croûte inférieure. Les roches des deux carrières enregistrent les conditions de pic de métamorphisme de 840-860 oC et 9-11 kbar a c. 2.71 Ga. Cet épisode est accompagné d’une production importante de leucosome (L1). Des leucosomes de seconde génération (L2) sont produits pendant la décompression à 6-7 kbar. La fin de l’épisode métamorphique est marquée par la transition granulites/amphibolites (< 640 oC) à c. 2.68 Ga. L’âge de dépôt maximum (c. 2.73 Ga) des zircons détritiques dans les métapelites indique un enfouissement rapide ( 0.17 cm.y-1). L’ensemble de ces données montre que la Zone Marginale Sud contient des sédiments déposés dans des conditions de marge active durant un phénomène de convergence. Les métapelites ont par conséquent subi leur métamorphisme et leur fusion partielle durant une collision continentale le long de la marge nord du craton du Kaapvaal à c. 2.7 Ga. Les formations leucocrates générées le long du trajet P-T-t possèdent une signature géochimique spécifique caractérisée par une teneur en K2O et FeO+MgO faible et une teneur élevée en CaO. La combinaison des observations de terrains, de la cartographie chimique et des analyses géochimiques permet de conclure que la majeure partie des leucosomes (L1) cristallisent avant le pic de métamorphisme après extraction du liquide de la source. En s’appuyant sur le laboratoire naturel qu’est la Zone Marginale Sud et utilisant une approche modélisatrice, cette étude présente les détails de la formation des leucosomes. Ce travail démontre que la formation de leucosomes pauvres en potassium dans les sédiments de la croûte inférieure et les processus qui contrôlent la chimie du résidu et des granites de type S sont les différences des volumes d’équilibration et l’hétérogénéité de la source couplées avec des pertes de liquide et diffusion de l’eau dans les structures d’anatexies / Anatexis is the first step in granite genesis. Partial melting in the lower crust may produce leucoratic features of unusual chemical compositions, very different from the final products of crustal differentiation. Therefore, the links that exists between some migmatites and crustal-derived granites can be ambiguous. This study is an investigation of the anatectic history of a high-grade terrain: the Southern Marginal Zone of the Limpopo Belt (SMZ), north to the Kaapvaal Craton in South Africa. The work involved an integrated field, metamorphic, geochemical and geochronogical study of the metasedimentary granulites from two separate quarries in the northern zone of the Southern Marginal Zone, the Bandelierkop quarry and the Brakspruit quarry, where Neoarchean high-grade partial melting features can be observed. The project has aimed to address two main issues: (1) to accurately constrain the pressure temperature conditions and the age of the metamorphic episode in the SMZ, with implication for the geodynamic processes near the end of the Archean, (2) to investigate the fluid-absent partial melting reactions that control formation of K2O-poor leucosomes and to understand the chemical relationships in the system source-leucosome-melt–S-type granite. The P-T-t record retained in the Bandelierkop Formation metapelites, constrained by phase equilibria modelling as well as zircon LA-ICP-MS geochronology, gives an insight into crustal differentiation processes in the lower crust. Rocks in both quarries indicate high-temperature metamorphism episodes with peak conditions of 840-860 oC and 9-11 kbar at c. 2.71 Ga with formation of leucosomes (L1) during the prograde path. Minor leucocratic features (L2) were produced during decompression to 6-7 kbar. The end of the metamorphic event is marked by the granulites/amphibolites facies transition (< 640 oC) at c. 2.68 Ga. The maximum deposit age for the detrital zircons in the metapelites (c. 2.73 Ga) indicates a rapid burial process ( 0.17 cm.y-1). Those evidences strongly support that the Southern Marginal Zone contains sediments deposited in an active margin during convergence, and that the metapelites were metamorphosed and partially melted as a consequence of continental collision along the northern margin of the Kaapvaal Craton at c. 2.7 Ga. The leucocratic features generated along this P-T-t path display an unusual chemistry with low K2O and FeO+MgO content and high CaO content. The combination of field observations, chemical mapping and geochemical analyses leads to the conclusion the major part of the leucosomes (L1) crystallized prior to syn-peak of metamorphism concurrent with melt extraction from the source. This study documents the details of leucosomes formation using field observations in the Southern Marginal Zone and numerical modelling. This work demonstrates that the formation of K2O-poor leucosome in the metasedimentary lower crust is controlled by the difference in volume of equilibration and heterogeneities within the migmatites. The partial melting of the source coupled with melt loss and water diffusivity within the melt transfer site is a potential mechanism to explain the chemical link in the system residuum–melt–S-type granite

Master of Science / Department of Geology / Matthew Brueseke / It is generally accepted that beneath flood basalt provinces, Cu-Ni-PGE sulfide deposits may be found (Ridley, 2013). The focus of this study is the Steens Basalt, a mid-Miocene flood basalt from the northern Great Basin (USA) which contains between ~5-400 ppm copper and is characterized by large plagioclase phenocrysts, some of which can contain primary inclusions of copper despite the chalcophile nature of Cu (Hofmeister and Rossman, 1985; Johnston et al., 1991). The purpose of this project is to identify the distribution of Cu among coexisting phases in Steens Basalt, test whether plagioclase crystals in Steens lavas can host Cu, even when Cu is not visible, and test whether sulfide minerals/droplets are present in Steens Basalt samples with low Cu concentrations. Samples of Steens lavas were examined for sulfide minerals via reflected light microscopy, Raman spectroscopy, and X-ray diffraction with a molybdenum tube. Using an electron microprobe, silicate minerals, oxides, glass, and sulfides were analyzed for their Cu concentration, as well as other major and trace element chemistry. Glass did not contain detectable Cu which precluded partition coefficient (Kd) calculations. Based on average Cu concentration for the non-sulfides, magnetite contains the most Cu, followed by (forsteritic) weathered olivine, pyroxene, olivine, plagioclase, and ilmenite. Copper sulfides were discovered in samples MB97-19 and MB97-76C with additional non-copper sulfides in MB97-76B. In conclusion, these results lay the groundwork for further investigation into potential copper sulfide reserves in the magma plumbing as with other flood basalt packages linked to economically important mineral deposits.

No description available.