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abstract: Volcanic eruptions are serious geological hazards; the aftermath of the explosive eruptions produced at high-silica volcanic systems often results in long-term threats to climate, travel, farming, and human life. To construct models for eruption forecasting, the timescales of events leading up to eruption must be accurately quantified. In the field of igneous petrology, the timing of these events (e.g. periods of magma formation, duration of recharge events) and their influence on eruptive timescales are still poorly constrained. In this dissertation, I discuss how the new tools and methods I have developed are helping to improve our understanding of these magmatic events. I have developed a method to calculate more accurate timescales for these events from the diffusive relaxation of chemical zoning in individual mineral crystals (i.e., diffusion chronometry), and I use this technique to compare the times recorded by different minerals from the same Yellowstone lava flow, the Scaup Lake rhyolite. I have also derived a new geothermometer to calculate magma temperature from the compositions of the mineral clinopyroxene and the surrounding liquid. This empirically-derived geothermometer is calibrated for the high FeOtot (Mg# = 56) and low Al2O3 (0.53–0.73 wt%) clinopyroxene found in the Scaup Lake rhyolite and other high-silica igneous systems. A determination of accurate mineral temperatures is crucial to calculate magmatic heat budgets and to use methods such as diffusion chronometry. Together, these tools allow me to paint a more accurate picture of the conditions and tempo of events inside a magma body in the millennia to months leading up to eruption. Additionally, I conducted petrological experiments to determine the composition of hypothetical exoplanet partial mantle melts, which could become these planets’ new crust, and therefore new surface. Understanding the composition of an exoplanet’s crust is the first step to understanding chemical weathering, surface-atmosphere chemical interactions, the volcanic contribution to any atmosphere present, and biological processes, as life depends on these surfaces for nutrients. The data I have produced can be used to predict differences in crust compositions of exoplanets with similar bulk compositions to those explored herein, as well as to calibrate future exoplanet petrologic models. / Dissertation/Thesis / Doctoral Dissertation Geological Sciences 2020

The Grenville orogeny was a protracted (~200 m.y.) series of “hot” magmatic- metamorphic events that contributed to the growth of the Laurentian margin in the late Mesoproterozoic. The granites contain remarkably high Zr content, lack xenocrysts, and become zircon saturated at high temperatures, which are all unusual for felsic magmas. The “hot Grenville granite” hypothesis is tested and use of high-Zr granitoids as potential zones of crustal magma generation through: U-Pb geochronology and cathodoluminescence imaging to assess inherited zircon components; quantitative modeling of zircon crystallization history using rhyolite-MELTS; and Ti-in-zircon thermometry. U-Pb zircon ages for two samples from the Virginia Blue Ridge are 1168 ± 25 Ma (2209 ppm Zr; Tzr = 1032°C) and 1050 ± 13 Ma (918 ppm Zr; Tzr = 898°C). A sample from the NJ – Hudson Highlands has been dated at 1018 ± 11 Ma (1238 ppm Zr; Tzr = 960°C). These samples produce crystallization histories that range over higher temperatures (983–1060°C) than colder, low-Zr counterparts and contain Ti concentrations of 2 to 86 ppm. This analytical approach will further the understanding of zircon’s utility and limitations as a proxy in granite petrogenesis, and constrain thermal models that produced uncommon lithospheric conditions that led to widespread hot granite production at a unique period in Earth history.

The Nahlin ophiolite represents one of the largest (~80 km long) and best-preserved ophiolites in the Cordillera of British Columbia and Yukon, Canada, yet it has been understudied compared to other ophiolites worldwide. Bedrock mapping at 1:20,000 scale in the Menatatuline Range area shows that the ophiolite is structurally disrupted with mantle bodies divisible into two massifs: Hardluck and Menatatuline. Studies of 30 samples show that both massifs consist of spinel harzburgites and minor lherzolites that have been strongly depleted by melt extraction (<2 wt % Al2O3 and ~45 wt % MgO). Clinopyroxene REE abundances determined by LA-ICP-MS illustrate different extents of depletion between the two massifs, with YbN varying from 2.3 – 5.0 and 1.7 – 2.2 in the Hardluck and Menatatuline massifs, respectively. Inversion modelling of the clinopyroxene REE abundances yields ~10 – 16% melting in the Hardluck massif and ~16 – 20% melting in the Menatatuline massif, with melt compositions that are compositionally similar to the gabbros and basalts proximal to the mantle rocks. All these extrusive and intrusive rocks in the ophiolite have an arc-signature, implying that the Nahlin ophiolite formed in a supra-subduction zone (SSZ) environment. The Nahlin peridotites document a two-stage evolution: depletion of a locally heterogeneous mantle source by hydrous fractional melting, followed by refertilization of the refractory harzburgite in the mantle wedge evidenced by LREE enrichment in clinopyroxene and whole-rock chemistry. This two-stage evolution is also recorded by the thermal history of the harzburgites. The REE-in-two-pyroxene thermometry has been reset following cryptic and modal metasomatism and relatively slow cooling, whereas major element two pyroxene geothermometry records temperatures varying from near solidus (~1290 °C) to ~800 °C, with the highest temperatures recorded in samples from the Menatatuline massif. The refractory nature of the Menatatuline harzburgites in combination with the arc-influenced volcanic geochemistry provides overwhelming evidence for a SSZ origin. Peridotite from the Hardluck massif displays characteristics of both abyssal and SSZ peridotites. These geochemical and geothermometric constraints can be reconciled by evolution of the Hardluck and Menatatuline massifs as two separate segments along a backarc ridge system, later juxtaposed by dextral strike-slip faulting. Alternatively, the Nahlin ophiolite may represent proto-forearc seafloor spreading associated with subduction initiation akin to the proposed origins of the Izu-Bonin-Mariana arc (Stern et al. 2012; Maffione et al. 2015). In any case, the geochemical data for peridotites and magmatic rocks herein require that the SSZ-type Nahlin ophiolite reside in the upper plate at an intraoceanic convergent margin. This interpretation has strong implications for models of northern Cordilleran tectonics, where the Cache Creek terrane is typically shown as a subducting ocean basin during Cordilleran orogenesis. / Graduate

Raman-Spektroskopie an kohligem Material (RSCM) ist eine häufig verwendete Methode, um die maximale Temperatur der Metamorphose oder die thermische Reife von Kohlen und organikreichen Sedimenten zu bestimmen. Für die Temperaturabschätzung wurden bereits mehrere Kalibrationskurven ermittelt, jedoch wird die Übertragbarkeit dieser Kalibrationen auf andere Labore durch methodische Aspekte eingeschränkt und die Vergleichbarkeit zwischen den Laboren dadurch reduziert. Die subjektive Auswertung von Spektren, das verwendete Messsystem und die Probenheterogenität bedingen die größte Streuung der Ergebnisswerte und ein Ansatz, mit dem Ziel die Vergleichbarkeit zu erhöhen, wurde formuliert. Um die Subjektivität der spektralen Auswertung zu veringern, wurde das ’IFORS’ (Iterative Fitting Of Raman Spectra) Programm geschrieben, das die automatische, Benutzer-unabhängige Auswertung von Raman-Spektren ermöglicht. Um die Streuung aufgrund des verwendeten Messsystems zu reduzieren, wurde ein Referenzprobensatz zusammengestellt, der einen Temperaturbereich von 160 °C bis 600 °C abdeckt. Während der Probenaufbereitung wurde Resonanz-Raman- Spektroskopie mit mehreren Anregungswellenlängen an dispersen Vitriniten durchgeführt, die diagenetische bis epizonale Druck- und Temperaturbedingungen erfahren hatten, um die Gleichwertigkeit der RSCM-Methode und Vitrinitreflexion zu ermitteln. Mit Hilfe des IFORS Programms wurde der ’scaled total area’ (STA) Raman Parameter ermittelt, der das Raman Spektrum von kohligem Material präzise beschreibt. Auf Grundlage der Resonanz-Raman Daten konnte gezeigt werden, dass die Methodiken der STA-Raman Spektroskopie und Vitrinitreflexion analog zueinander sind, dass die STA-RSCM Methode gegenüber der Probenaufbereitung, insbesondere dem Polieren, robust ist, und dass die Resonanz-Raman Spektren der Vitrinite eine zweistufige molekulare Entwicklung während der Inkohlung und Graphitisierung aufzeichnen. Während der ersten Stufe, die kurz nach dem Durchschreiten des Gas-Fensters endet, wachsen vor allem lineare, polyzyklische, aromatische Kohlenwasserstoffe, während in der anschließenden zweiten Stufe kondensierte Formen von polyzyklischen, aromatischen Kohlenwasserstoffen wachsen. Um die Raman Spektren von metamorphem, kohligem Material zu beschreiben, wurde die STA-RSCM Methodik erweitert und erfolgreich gegen die Temperaturinformation des Referenzprobensatzes kalibriert, so dass ein neues, überarbeitetes RSCM-Geothermometer vorgestellt werden konnte, das über einen Temperaturbereich von 160°C bis 600°C zulässig ist. Der Referenzprobensatz steht öffentlich zur Verfügung und es wird erwartet, dass der Probensatz verbessert werden kann, wenn er um Proben aus der wissenschaftilchen Gemeinschaft erweitert wird. Wenn beide Ansätze, die STA-RSCM Methodik und der Referenzprobensatz, miteinander kombiniert werden, erhöht sich die Vergleichbarkeit zwischen den Laboren und gleichzeitig steht diese geothermometrische Methode allen Laboren zur Verfügung.

The Pacific Rim Terrane in British Columbia is a group of fault-bound forearc metasedimentary and metaigneous rocks subcreted to Wrangellia, comprising three lithological units: the Leech River Complex (LRC), the Pandora Peak Unit (PPU), and the Pacific Rim Complex. Of these three, the LRC and PPU were subject to an elevated thermal metamorphic event which locally overprinted typical low temperature, medium pressure forearc assemblages with low greenschist through amphibolite facies assemblages. The field study shows that biotite, garnet and staurolite isograds occur concentrically in the LRC, centered on the Leech River fault, which separates the Pacific Rim Terrane from the underlying Metchosin Igneous Complex of the Crescent terrane. Local thermal overprint in the PPU is sub-biotitic and is characterized by local replacement of prehnite-pumpellyite and lawsonite-bearing assemblages with muscovite ± chlorite. Multi-method geothermobarometry shows peak metamorphic temperatures from ~230 °C in the northern PPU to ~600 °C near the Leech River fault at ~4 kbar, and isotherms are continuous across the LRC-PPU boundary. The interfoliated Tripp Creek metabasites and Eocene Walker Creek intrusions do not control the distribution of isotherms, and syn-metamorphic felsic sills rarely have contact aureoles. Intercalated metabasites show two distinct rare earth element (REE) patterns, including NMORB-like light REE depletion among most Tripp Creek metabasites, and light REE enrichment in PPU metabasites. The lack of thermal aureoles associated with metabasites, and interlayered garnetite bands with negative Ce-anomalies attributed to seafloor hydrothermal processes, suggest the Tripp Creek metabasites are not syn-metamorphic sills and formed prior to accretion. The subcretion of then recently formed oceanic crust belonging to the Crescent terrane is identified as the probable cause of anomalously high temperature forearc conditions, as well as possible proximity to an Eocene mid ocean ridge. The high temperature metamorphic rocks in the Pacific Rim Terrane document the conversion of inherited primary pyrite to pyrrhotite in carbonaceous metasediments. S-inclusive pseudosections for LRC protoliths predict a low temperature (<420 °C) narrow pyrite desulfidation window that produces pyrrhotite and releases negligible S to the fluid phase. Conversely, sulfide petrography in the LRC shows pyrite can persist up to ~550 °C as inclusions in andalusite and staurolite porphyroblasts, as well as possibly in the rock matrix. S contents in carbonaceous pelites show a marked reduction at medium grade, associated with a dearth of visible sulfide in LRC phyllites. Sluggish pyrite desulfidation, pyrrhotite desulfidation, and terrane-scale S mobility are interpreted as the driver for mobility of intra-terrane sourced Au, leading to the formation of a hypozonal orogenic Au deposit in the central LRC. / Graduate / 2022-06-11

The Station Creek Igneous Complex (SCIC) is one of the largest Middle-Late Triassic plutonic bodies in the northern New England Orogen of Eastern Australia. The igneous complex comprises of five plutons - the Woonga Granodiorite (237 Ma), Woolooga Granodiorite (234 Ma), Rush Creek Granodiorites (231 Ma) and Gibraltar Quartz Monzodiorite and Mount Mucki Diorite (227 Ma respectively), emplaced as high-level or epizonal bodies within the Devonian-Carboniferous subduction complex that resulted from a westward subduction along the east Australian margin. Composition of the SCIC ranges from monzogabbro to monzogranite, and includes diorite, monzodiorite, quartz monzodiorite and granodiorite. The SCIC has the typical I-type granitoid mineralogy, geochemistry and isotopic compositions. Its geochemistry is characteristics of continental arc magma, and has a depleted-upper mantle signature with up to 14 wt% supracrustal components (87Sr/86Srinitial = 0.70312 to 0.70391; Nd = +1.35 to +4.9; high CaO, Sr, MgO; and low Ni, Cr, Ba, Rb, Zr, Nb, Ga and Y). The SCIC (SiO2 47%-76%) has similar Nd and Sr isotopic values to island-arc and continentalised island-arc basalts, which suggests major involvement of upper mantle sourced melts in its petrogenesis. SCIC comprises of two geochemical groups - the Woolooga-Rush Greek Granodiorite group (W-RC) and the Mount Mucki Diorite-Gibraltar Quartz Monzodiorite group (MMD-GQM). The W-RC Group is high-potassium, calc-alkalic and metaluminous, whereas the MMD-GQM Group is medium to high potassium, transitional calc-alkalic to tholeiitic and metaluminous. The two geochemical groups of the SCIC magmas are generated from at least two distinct sources - an isotopically evolved Neoproterozoic mantle-derived source with greater supracrustal component (10-14 wt%), and an isotopically primitive mafic source with upper mantle affinity. Petrogenetic modeling using both major and trace elements established that the variations within respective geochemical group resulted from fractional crystallisation of clinopyroxene, amphibole and plagioclase from mafic magma, and late fractionation of alkalic and albitic plagioclase in the more evolved magma. Volcanic rocks associated with SCIC are the North Arm Volcanics (232 Ma), and the Neara Volcanics (241-242 Ma) of the Toogoolawah Group. The major and trace element geochemistry of the North Arm Volcanics is similar to the SCIC, suggesting possible co-magmatic relationship between the SCIC and the volcanic rock. The age of the North Arm Volcanics matches the age of the fractionated Rush Creek Granodiorite, and xenoliths of the pluton are found within epiclastic flows of the volcanic unit. The Neara Volcanics (87Sr/86Sr= 0.70152-0.70330, 143Nd/144Nd = 0.51253-0.51259) differs isotopically from the SCIC, indicating a source region within the HIMU mantle reservoir (commonly associated with contaminated upper mantle by altered oceanic crust). The Neara Volcanics is not co-magmatic to the SCIC and is derived from partial melting upper-mantle with additional components from the subducting oceanic plate. The high levels emplacement of an isotopically primitive mantle-derived magma of the SCIC suggest periods of extension during the waning stage of convergence associated with the Hunter Bowen Orogeny in the northern New England Orogen. The geochemical change between 237 to 227 Ma from a depleted-mantle source with diminishing crustal components, to depleted-mantle fractionate, reflects a fundamental change in the source region that can be related to the tectonic styles. The decreasing amount of supracrustal component suggests either thinning of the subduction complex due to crustal attenuation, leading to the late Triassic extension that enables mantle melts to reach subcrustal levels.