Experimental Insights Into Magma and Volatile Transport Beneath Erebus Volcano, Antarctica

An unexpected journey: Experimental insights into magma and volatile transport beneath Erebus volcano, Antarctica Kayla Iacovino University of Cambridge Department of Geography Darwin College A thesis submitted for the degree of Doctor of Philosophy February 2014 Declaration of Originality I certify that this dissertation is the result of my own work and includes nothing that is the outcome of work done in collaboration, except where specifically indicated in the text. I confirm that it does not exceed the word limit as mandated by the degree committee of the Department of Geography and does not contain work that has been submitted for another degree, diploma, or other qualification at any other university. Kayla Iacovino “If you wish to make a phonolite from scratch, you must first invent the universe.” Dedication It’s been a long (and unexpected) journey. I’ve learned about geology, fieldwork, friendship. Science, life, and love. I am so different from the person I was when I started this PhD. I suppose all of us are. This section, which could never be long and extensive enough, is dedicated to just a handful of the people that helped me get here and to those who will no doubt continue to be an inspiration to me. First and foremost, I would like to acknowledge my loving boyfriend, Andrew Britton, and my cat Jazzmyn, both of whom travelled across the world for me many times over, provided support every day, and stuck with me through the thick and thin. Iwasgiventhegiftsofencouragementandstrengthfromsomany long Skype conversations with my mother, Susan Kayler, and my best friend, Emily Allender. My father, Mark Iacovino, never let me down and always provided a place to go or a loving hand when I needed it most. My brother, Matt Larson, inspires me everyday with the amaz- ing things he does in life, and he has taught me what is possible in this world. My experience here would never have been complete without much gal- livanting around the globe done in the name of science. Where would I be without Nial Peters, Tehnuka Ilanko, Kelby Hicks, and Yves Mous- sallam (that latter of whom I learned a lot from, albeit the hard way)? If I were religious, I would thank God on my knees that Clive Oppen- heimer and James Hammond never got me arrested in North Korea. Coming home would never have been complete were it not for Talfan Barnie, with whom I spent many long nights searching for the last open pub in Cambridge and musing on the finer points in life (beer and science). My supervisor, Clive Oppenheimer, taught me that some people really never grow up (even after they have a baby) and that you should always be ready for the next opportunity, which can present itself at a moment’s notice. Phil Kyle taught me that some people really, really never grow up, and that you should always be ready for that next handful of cow dung, which can present itself at a moment’s notice. Bruno Scaillet taught me to keep my chin up in the face of harsh experimental realities (exploding experiments). Last, and certainly not least, I want to thank Gordon Moore. Al- though Gordon didn’t supervise me in any official capacity during my PhD, I give him credit for sculpting my malleable undergraduate brain into something that was ready to take on the challenges I’ve faced since leaving Arizona. I can’t imagine navigating academia without his teachings on science, experiments, life, wine, Italian politics, and more wine. Gordon will always be the person I look to as the shining example of a good researcher and a good person. Abstract Erebus is a well-studied open-vent volcano located on Ross Island, Antarctica (77◦ 32’ S, 167◦ 10’ E). The volcano is the focus of ongoing research aimed at combining petrologic data and experiments with surface gas observations in order to interpret degassing histories and the role of volatiles in magma differentiation, redox evolution, and eruptive style. This research focus has been driven in part by an abundance of studies on various aspects of the Erebus system, such as physical volcanology, gas chemistry, petrology, melt inclusion research, seismic, and more. Despite this large data set, however, interpretations of Erebus rocks, particularly mafic and intermediate lavas, which are thought to originate from deep within the magmatic plumbing system, have been hindered due to a lack of experimental data. Experimental petrology is a common tool used to understand volcanic plumbing systems and to tie observations made at the Earth’s surface to the deep pro- cesses responsible for driving volcanic activity. Experimental petrologists essen- tially recreate natural magma chambers in miniature by subjecting lavas to conditions of pressure, temperature, and volatile chemistry (P-T-X) relevant to a natural underground volcanic system. Because many important parameters can be constrained in the laboratory, the comparison of experimental products with naturally erupted ones allows for an understanding of the formation conditions of the rocks and gases we see at the surface. In this thesis, I have employed experimental and analytical petrological techniques to investigate the magmatic plumbing system of Erebus volcano. Broadly, the research is focused on volatiles (namely H2O, CO2, and S species) in the Ere- bus system: their abundances, solubilities, interactions, evolution, and ultimate contributions to degassing. Specifically, three key themes have been investigated, each employing their own experimental and analytical techniques. Firstly, the mixed volatile H2O-CO2 solubility in Erebus phonotephrite has been investigated under P-T-X conditions representative of the deep plumbing system of Erebus. Understanding the deep system is crucial because the constant supply of deeply derived CO2-rich gases combined with a sustained energy and mass input into the lava lake suggests a direct link between the phonolite lava lake and the volcano’s ultimate mantle source via a deep mafic plumbing system. Secondly, I have mapped the phase equilibria and evolution of primitive, intermediate, and evolved Erebus lavas. The chemistries of these experimental products span the full range of lavas on Ross Island and help to constrain magmatic evolution from basanite to phonolite as well as to elucidate the geometry of the deep Ross Island plumbing system. Finally, lower-pressure experiments representing the shallow plumbing system at Erebus have been performed in order to understand the transport properties of sulfur in alkaline magma. Experiments were performed on natural Erebus basanite and phonolite, which represent the most primitive and evolved lavas from Erebus. A distinct cocktail of C-O-H-S fluid was equilibrated with each experiment, and a wide range of experimental oxygen fugacities was explored. Overall, experiments from this work are the first to place constraints on the en- tire magma plumbing system of Erebus volcano. In addition, experimental results foster a new understanding of non-ideal gas behavior at high pressure, the affinity of CO2 to deeply sourced rift magmas, and the effect of alkalis on fluid transport capabilities in melts. Nomenclature Repeated Symbols ✏ Absorption coefficient γi Fugacity coefficient of component i ! Acentric factor a Empirical coefficient in Redlich-Kwong equation of state (bar cm6 K1/2/mole2) · · b Empirical coefficient in Redlich-Kwong equation of state (cm3/mol) fi Fugacity of component i KD Partition coefficient of some component between the superscripted phases KF Equilibrium constant of formation m Mass P Pressure Pi Partial pressure of component i Ptot Total pressure R Gas constant (= 83.12 cm3 bar/deg mol unless otherwise indicated) · · T Temperature V Volume vii Xi Mole fraction of component i Superscripts fl Fluid m Melt pure Property of a pure species at P and T of interest Subscripts c Refers to variable at critical point i Refers to component i j Refers to component j viii Contents Contents ix List of Figures xiii 1Introduction 1 1.1 Relevant Volcanological Background . 1 1.2 TheChemistryofRossIslandLavas. 9 1.2.1 MineralogyofDVDPandELrocks . 12 1.2.2 RossIslandMeltInclusions . 13 1.3 ExperimentalPetrologyBackground . 16 1.4 Research Rationale and Objectives . 19 1.4.1 Mixed volatile solubility in Erebus magma . 19 1.4.2 Phase Equilibria of Intermediate and Primitive Erebus Lavas 21 1.4.3 C-O-H-SFluidsinErebusMagma. 23 1.4.4 ThisThesis,Overall . 25 1.5 Comments on Previously Published or Submitted Materials . 26 2NaturalSampleSelectionandPreparationofStartingMaterials29 2.1 StartingMaterials............................ 29 2.1.1 PhonotephriteAW-82038. 29 2.1.2 BasaniteKI-04 ......................... 33 2.1.3 PhonoliteERE-97018. 35 3H2O-CO2 Solubility in Erebus Phonotephrite Magma 36 3.1 Abstract . 36 ix CONTENTS 3.2 Introduction . 37 3.2.1 The role of alkalis in controlling volatile solubility . 37 3.2.2 Disagreement between solubility models for mafic alkaline melts . 38 3.3 Experimentalmethods . 41 3.3.1 Preparationofexperimentalcapsules . 41 3.4 Analytical techniques . 42 3.4.1 H2O–CO2 fluid manometry . 42 3.4.2 Infrared spectroscopy . 44 3.4.3 Electronmicroprobe . 47 3.4.4 Establishment of equilibrium . 47 3.5 Results . 50 3.5.1 Iron oxidation state and experimental oxygen fugacity . 50 3.5.2 H2O–CO2 solubility in phonotephrite . 51 3.5.3 Thermodynamic modeling of mixed-volatile solubility data and comparison with other solubility models . 51 3.5.4 Determination of empirical solubility relationships . 55 3.6 Discussion . 58 3.6.1 Saturation pressures and fluid compositions of primitive Ere- bus magmas . 58 3.6.2 Determining the source of volatiles released in explosive erup- tions through the Erebus lava lake . 59 3.7 Conclusions ............................... 62 4PhaseEquilibriumConstraintsontheDeepandIntermediate Magma Plumbing Beneath Ross Island 65 4.1 Abstract . 65 4.2 ExperimentalOverview. 66 4.3 ExperimentalTechniques. 67 4.3.1 Preparation of Experimental Capsules .

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