Exposed on Vancouver Island, British Columbia, the Jurassic Bonanza arc is believed to represent the southerly continuation of the Talkeetna arc. Small bodies of mafic and ultramafic cumulates within deeper plutonic levels of the arc constrain the fractionation pathways leading from high-MgO basalt to andesite-dacite compositions. The removal of amphibole from the most primitive non-cumulate compositions controls the compositions of mafic plutons and volcanics until the onset of plagioclase crystallization. This removal is accomplished by the intercumulus crystallization of large amphibole oikocrysts in primitive olivine hornblendite cumulates. Experimental hornblende compositions that crystallize from high-MgO basalts similar to primitive basalts from the Bonanza arc show a good correlation between octahedral Al in hornblende and pressure, and provide a means of estimating crystallization pressures during differentiation of primitive arc basalt. Application of an empirical barometer derived from experimental amphibole data (P = Al(6)/0.056 – 0.143; r2 = 0.923) to natural hornblendes from this study suggests that crystallization of primitive basalts took place at 470-880 MPa. Two-pyroxene thermometry gives a result of 1058 +/- 91 ºC for the only olivine hornblendite sample with both pyroxenes. Lever rule calculations require the removal of 30-45 % hornblende from the most primitive basalt compositions to generate basaltic andesite, and a further 48% crystallization of hornblende gabbro to generate dacitic compositions. Hornblende removal is more efficient at generating intermediate compositions than anhydrous gabbroic fractionating assemblages, which require up to 70% crystallization to reach basaltic andesite from similar starting compositions. There are no magmatic analogues to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will push the bulk arc composition to high-Mg# andesite. Garnet removal appears to be a key factor in producing bulk continental crust.

This dissertation combines mineralogical data and petrographic and field observations with geochemical analysis (major, trace and isotope) to provide new insights into the hydrology and geochemistry of mid-ocean ridge hydrothermal systems. Two study areas were chosen to study two different aspects of hydrothermal circulation: high-temperature on-axis hydrothermal systems were studied using samples from the Hess Deep Rift (Cocos Plate, Equatorial Pacific) and low-temperature off-axis hydrothermal systems were studied at the Troodos Ophiolite in Cyprus. Significant findings include the documentation of a previously unknown warm fluid that pervades the lavas leaching Li from newly formed crust. This finding corroborates a model of broad hydrothermal discharge in the sheeted dikes. In the off-axis low-temperature regime, lateral flow of warm fluid is documented in the lavas, advecting heat from the oceanic lithosphere, with minor geochemical changes to the lavas. The sedimentary cover was found to influence alteration in two ways. The longer an area remains unsedimented allowing the free ingress and egress of seawater, the deeper the enrichment of alkali metals is observed. The maximum enrichment in alkali metals (K, Rb, Cs) however, is similar in both locations. The sedimentary cover can also modify the seawater before it becomes impermeable to fluid flow; early metaliferrous oxide sediments react with seawater, creating a fluid that mobilizes and fractionates the REEs and Y. The fractionation results in negative Ce anomalies, positive Eu anomalies, and negative Y anomalies. Basalts altered under these conditions also lack the ubiquitous Fe-oxides and Fe-oxyhydroxides that are commonly associated with alkali metal uptake. In situ trace element analysis of alteration minerals formed at low-temperature confirmed that secondary phyllosilicates are strongly enriched in alkali metals (K, Rb, Cs and Li), Ba is found in adularia and zeolites, Sr is hosted in carbonates, and no phases were found to be enriched in U. The concentrations of K2O, Rb, Cs (as well as B) are highest in celadonites, whereas Li concentrations are highest in smectites (saponite, Al-saponite, beidellite) and smectite-chlorite mixtures, and much higher than previously reported. Alkalis are also taken up into palagonite, with Li having the highest concentrations, over 1000 ppm in one analysis. Crystal chemical factors were found to be the dominant control on trace element uptake, and for the phyllosilicates no correlation was found between the temperature, age of the crust, texture of the phyllosilicates. In phyllosilicates the K, Rb and Cs are adsorbed as exchange cations, with enrichment (Cs > Rb > K) increasing with decreasing hydration energy, whereas the uptake of Li and B does not correlate with the hydration energy. Lithium concentrations also do not correlate with the Mg content, suggesting substitution of Li for Mg is not the only mechanism of Li uptake into phyllosilicates as has been suggested. / Graduate

It is suggested that the Mafic Units and HS are allochthonous and were emplaced onto the WGR during an early stage of the Caledonian Orogeny. All units, including the Basement Gneisses, have suffered retrogression during a late extensional phase which continued into at least the Middle Devonian.

The Lofoten-Vesterålen province of North Norway consists almost exclusively of Precambrian granulite-facies rocks. The oldest rocks in the province are monzonitic and dioritic migmatitic gneisses, the protoliths of which were formed at 2.7 Ga. The migmatites are overlain by a series of supracrustal gneisses, from 2.1 Ga, largely volcanogenic in origin, but with interbedded marbles and banded ironstones. The first occurrence of marble in western Lofoten is reported. Deposition in a subsiding back-arc basin or in an Andean- type environment on a thin continental margin is inferred. Both gneiss sequences were intruded by basic rocks at 1.8 Ga. The basic rocks could not have been formed simply by extraction from the mantle at 1.8 Ga. The required contribution from 2.7 Ga migmatites could be as much as 37%, but less if contamination took place via anatectic melts. The first report of eclogitic rocks from the Lofoten-Vesterålen province is made in this study; their formation is associated with shear deformation Both gneiss sequences and the basic rocks were intruded by mangeritic rocks at 1.8 - 1.7 Ga. Their chemical compositions can be explained by fractional crystallization from magmas formed from 2.7 Ga and 2.1 Ga gneisses and 1.8 Ga mantle-derived magmas. Parameters derived from Rb-Sr, Sm-Nd and U-Pb systems to express the relative proportions of crust and mantle contributions to the mangerites mutually correlate, supporting the crust-mantle source model for the mangerites. Mixing calculations suggest that the late Archaean contributes in excess of 50% by mass for almost all mangerites. Anatectic veins present, especially in the Moskenesøy supracrustal gneisses, are inferred to represent partial melts which coalesced to form the mangerites at higher structural levels. Anatexis was caused by basaltic underplating associated with limited crustal extension. Later rock-forming events were the emplacement of dolerite dykes; the 1.65 Ga Lødingen Granite; the Leknes Group metasediments and the Caledonian granite pegmatites.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 26, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dissertation advisor: Dr. Mian Liu. Vita. Includes bibliographical references.

Typescript. Includes vita and abstract. Includes bibliographical references (leaves 155-177). Also available online in Scholars' Bank; and in ProQuest, free to University of Oregon users.

Thesis (M.S.)--University of Wisconsin--Madison, 1974. / Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

Exposed on Vancouver Island, British Columbia, the Jurassic Bonanza arc is believed to represent the southerly continuation of the Talkeetna arc. Small bodies of mafic and ultramafic cumulates within deeper plutonic levels of the arc constrain the fractionation pathways leading from high-MgO basalt to andesite-dacite compositions. The removal of amphibole from the most primitive non-cumulate compositions controls the compositions of mafic plutons and volcanics until the onset of plagioclase crystallization. This removal is accomplished by the intercumulus crystallization of large amphibole oikocrysts in primitive olivine hornblendite cumulates. Experimental hornblende compositions that crystallize from high-MgO basalts similar to primitive basalts from the Bonanza arc show a good correlation between octahedral Al in hornblende and pressure, and provide a means of estimating crystallization pressures during differentiation of primitive arc basalt. Application of an empirical barometer derived from experimental amphibole data (P = Al(6)/0.056 – 0.143; r2 = 0.923) to natural hornblendes from this study suggests that crystallization of primitive basalts took place at 470-880 MPa. Two-pyroxene thermometry gives a result of 1058 +/- 91 ºC for the only olivine hornblendite sample with both pyroxenes. Lever rule calculations require the removal of 30-45 % hornblende from the most primitive basalt compositions to generate basaltic andesite, and a further 48% crystallization of hornblende gabbro to generate dacitic compositions. Hornblende removal is more efficient at generating intermediate compositions than anhydrous gabbroic fractionating assemblages, which require up to 70% crystallization to reach basaltic andesite from similar starting compositions. There are no magmatic analogues to bulk continental crust in the Bonanza arc; no amount of delamination of ultramafic cumulates will push the bulk arc composition to high-Mg# andesite. Garnet removal appears to be a key factor in producing bulk continental crust.

xviii, 177 p. : ill., maps. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / This dissertation explores several important consequences of H 2 O-rich fluids in magmatic and ore-forming systems within continental arc crust. North Sister, a stratovolcano in the Oregon High Cascades, provides a window into magma generation processes in the deep crust. Eruption of a remarkably limited basaltic andesite composition over the lifespan of this volcano may reflect last equilibration of mantle derived magma within a deep crustal hot zone. High pressure, water-undersaturated phase equilibrium experiments show that an anhydrous, augite-rich gabbro at ∼12 kbar (40 km depth) and ∼ 1175°C is the most probable lithology with which North Sister basaltic andesite with ∼3.5 wt% H 2 O last equilibrated within the deep crust before erupting. While magma often erupts at the planets surface as at North Sister, a greater volume never reaches the surface and solidifies within the upper crust. Exsolution of magmatic fluids is an inevitable consequence of crystallization of hydrous crustal magmas. The fate of these fluids is the focus of the remainder of this dissertation. Modeling of CO 2 and H 2 O variations during crystallization of granitic magma reveals that exsolution of a large mass of fluid occurs only after CO 2 is largely degassed, creating ideal conditions for hydrofracturing and formation of porphyry copper deposits. CO 2 and H 2 O solubility relations suggest that H 2 O-rich magma was required to produce the porphyry-Cu-Mo deposit at Butte, Montana, which may explain its distinctively deep generation. Electron microprobe analyses of Ti in quartz and Zr in rutile in samples from Butte yield porphyry magma temperatures (630-770°C) that overlap substantially with hydrothermal vein temperatures (<430-750°C). Veins display large temperature ranges (50-250°C) that signify variable degrees of cooling of hot magmatic fluids upon contact with cooler wall rock during vein growth. Modeling of Ti diffusion in quartz suggests that individual dikes and veins likely cooled over short timescales (10s-1000s years), indicating that porphyry systems may evolve by episodic magmatic fluid injections with discrete thermal spikes. Modeling of Ti diffusion in quartz combined with electron backscatter diffraction maps show that small hydrothermal quartz veins likely formed by epitaxial growth. This dissertation includes co-authored material both previously published and in preparation for submission. / Committee in charge: A. Dana Johnston, Chairperson, Geological Sciences; Mark Reed, Member, Geological Sciences; Paul Wallace, Member, Geological Sciences; Richard P. Taylor, Outside Member, Physics

In recent decades there has been an increased interest in the carbon content of Earth’s geochemical reservoirs due to the impact of atmospheric carbon on the habitability of our planet. Earth’s interior likely hosts a greater mass of carbon than that of the oceans, atmosphere and crust combined, which has buffered the carbon content of the atmosphere over geological time. Yet only a few direct measurements of carbon from the upper mantle, and none from the lower mantle, have been made. Undegassed basalts erupted at mid-ocean ridges have previously been used to estimate the carbon content of the upper mantle. However, due to the low solubility of carbon within silicate melt, these undegassed basalt suites are rare. The majority of basalts have lost their mantle carbon information en route to eruption through the crust. Various crustal processes act to modify the geochemistry of melts before eruption, therefore it is important to be able to characterise the effect of these processes to better interpret the volatile signals preserved in erupted products. Pressure, and therefore depth, is a key parameter controlling volatile solubility and can be estimated using a variety of igneous barometers. This thesis presents results from crys- tallisation experiments conducted on basaltic glass from the Miðfell eruption, Iceland. The experiments provide new data that has been used to test a variety of barometers and crystalli- sation models used by igneous petrologists, and could aid future barometer recalibration. A key part of this work was the development of an experimental method for stabilising 5 kbar conditions in a piston cylinder apparatus. The experiments have shown that clinopyroxene- liquid barometry is more reliable than multi-reaction barometry. However, knowledge of equilibrium clinopyroxene compositions is crucial for accurately determining pressure using the clinopyroxene-liquid barometer. More experiments conducted at mid-crustal pressures are required for a full recalibration of these barometers. The results of testing igneous barometers and crystallisation models have been applied to two suites of olivine-hosted melt inclusions from the Kistufell and Miðfell eruptions to help determine the melt evolution history of these basalts. These eruptions were targeted due to previously measured noble gas isotopic ratios that suggest a primordial mantle component present in their melting regions, and therefore evoking the possibility that they could hold information about deep mantle carbon. Barometry suggests that Miðfell phases equilibrated, and therefore crystallised, at mid-crustal pressures (5–7 kbar), which could allow for the entrapment of undegassed melt inclusions within olivine. The two melt inclusion suites were found to differ in trace element variability, with the observation that the more trace element enriched eruption, Kistufell, had lower relative trace element variability than the more depleted eruption, Miðfell. Several processes, both in the crust and the mantle, are likely responsible for the level of trace element enrichment and variability, including extent of mantle melting, source heterogeneity, and melt transport. The depleted nature of the Miðfell melt inclusions has allowed them to preserve some of the highest CO$_2$/Ba and CO$_2$/Nb ratios ever recorded in basaltic glass, with ratios over five times greater than undegassed mid-ocean ridge basalt values. This carbon enrichment is not due to any crustal melt modification process, but rather pertaining to lower mantle carbon-rich lithologies that have been tapped by the Icelandic mantle plume. The carbon reservoir beneath Miðfell is estimated to contain 744 $\pm$ 188 ppm carbon, 15 times greater than the depleted upper mantle. This value matches estimates of bulk mantle carbon from planetary mass balance calculations and provides evidence for carbon-rich domains within the Earth.