Browsing by Author "Lee, Cin-Ty A"

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    Characteristics of Serpentinized Peridotites from Collisional Settings: A Case Study from Domenigoni Valley, California
    (2016-12-02) Malouta, Alexandra Julia; Lee, Cin-Ty A
    Peridotites are infrequently seen at the earth’s surface, making the glimpses of mantle processes they reveal invaluable. An unusual metaperidotite outcrop in Domenigoni Valley, CA offers insight into subduction zone processes associated with the accretion of western North America. These serpentinized dunitic peridotites, exposed at the northernmost tip of the Peninsular Ranges Batholith arc, display a melt-depleted pyroxene-poor mineralogical composition. High forsterite contents of olivines and high chromium number in chrome spinels indicate that these highly melt-depleted samples are of forearc origin (Arai, 1994), further substantiated by low concentrations of incompatible elements. Serpentinization fluids appear to have refertilized light rare earth elements (LREEs) in these samples without affecting the concentrations of major and minor elements. Calculations of melt depletion based on heavy rare earth element (HREE) concentrations of olivines and whole rock glasses indicate melt depletion of up to 25%. Fostering a better understanding of mantle behavior associated with arc accretionary processes may help to illuminate the subtleties of continental crust formation.
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    Examination of magmatic differentiation processes in the formation of intermediate and silicic composition magmas: constraints from regional and global geochemical systematics
    (2017-04-21) Farner, Michael Joseph; Lee, Cin-Ty A
    Granitic rocks and mafic enclaves from the Bernasconi Hills pluton in the Peninsular Ranges Batholith, California, USA provide constraint on the extent and spatial lengthscale of mafic-felsic interaction in upper crustal granitic plutons. Further detailed mapping of mineralogical variations in the pluton and among enclaves highlights late-stage magmatic processes such as segregation of evolved residual melt and reactions between solidified enclaves and granitic melts. Collectively, the field, mineralogical and geochemical systematics of the Bernasconi Hills pluton show that mafic-felsic mixing between host granitic magma and partially solidified mafic enclaves was limited spatially, on the order of meters, and only proceeded to an early, incipient stage. Phosphorus-zirconium systematics indicate that the pluton developed through a combination of crystal fractionation and incipient mixing, in contrast to volcanic rocks, where magmatic evolution is primarily driven by crystal fractionation. Further examination of global geochemical systematics of subaerial arc lavas show a correlation between SiO2 and crustal thickness as expressed by elevation. Arc lavas become more compositionally evolved with increasing elevation/crustal thickness, tend towards increasingly iron-depleted, or calc-alkaline, compositions and show evidence for garnet fractionation at depth in thick arcs. Coupled thermal and thermodynamic compositional modeling indicates that crustal thickness controls arc lava compositions by modifying the thermal lifespan and segregation times of melt in crustal magma chambers.
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    Interplays between magmatism, crustal deformation, surface erosion and long-term climate on the rise and fall of continental arcs
    (2018-04-16) Jiang, Hehe; Lee, Cin-Ty A
    Continental arc is one of the most dominant topographic features on Earth with complicated petrogenesis, active volcanism and rapid erosion. Interplays between the deep and surface processes in continental arcs play an important role in shaping the earth. The overall objective of this study is to develop a better understanding of the interconnections between various processes such as magmatism, uplift, surface erosion in continental arcs, and their influences on long term development of the atmosphere and hydrosphere. Continental arcs are characterized by episodic voluminous magmatic flare-ups in the time scale of tens to hundreds of millions of years. Due to the interaction of magma with sedimentary carbonates stored in the continental upper plate, flare-ups in continental arc might result in enhanced CO2 concentration in the atmosphere and greenhouse climate. However, development of continental magmatic arc often accompanied by rapid arc unroofing and erosion due to magmatic/tectonic thickening of the crust, thus continental arcs likely enhance the chemical weathering flux, in turn increasing the CO2 sink. With these feedbacks, it is not clear how long-term climate responds to the variability in the tectonic forcings in the continental arcs. In the first two chapters, I explored the dynamic linkage between magmatism and erosion in continental arcs and evaluated the carbon input and output associated with these processes. I found that during the rise and fall and continental arcs, the arc serves as either a carbon source or sink depending on the stage of the arc life. I propose that the development of continental arcs increases weatherability through mountain building processes, and therefore may increase the strength of the global negative feedback between silicate weathering and climate. In the rest studies, I investigated other processes associated with continental arc development. In Chapter 4, I investigated geochemistry of pseudotachylite from an ancient shear zone in a continental arc. This study attempts to obtain insights of the physics behind earthquake such as thermodynamic conditions and stress state in the shear zone from a geochemical aspect. As the rise and fall of the continental arc can drive changes in the subsurface hydrologic conditions, groundwater products can serve as proxies for the tectonic and climatic forcings in tectonic basins. In Chapter 5, I explored the prospects of using U-Pb dating of petrified (silicified) wood as means of quantifying ancient continental hydrology.
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    Micro to macro: Investigating magmatic processes from crystals to satellites
    (2022-11-28) Phelps, Patrick Richard; Lee, Cin-Ty A
    Magmatic systems are a source of both joy and trepidation for humankind, providing the valuable resources necessary for modern life yet producing hazards for those living near and far away. A better understanding of the processes that produce both the natural resources and the natural hazards that are inherent in magmatic systems is therefore important. In this dissertation, I explore the resources side by determining crystal growth rates in pegmatites and the hazards side by studying melt migration in crystal mushes to explain surface deformation. Pegmatites are rocks made up of large crystals (centimeter to meter scale) and are home to many economically essential elements. Ascertaining how quickly the crystals grow provides us with a better fundamental picture of how ore hosting pegmatites come to be. I show how micron-scale trace element profiles in quartz from the Stewart pegmatite are caused by crystal growth rates as fast as a meter per day. I also investigate lithium isotopes in the same quartz and whether their profiles also show signs of rapid growth. I find that the isotopes are more sensitive to changes in the amount of lithium remaining in the growth environment. Both trace elements and isotopes then lend separate insight into pegmatite formation overall. Surface uplift at a volcano is typically cause for alarm, raising the specter of an impending eruption. I demonstrate how surface uplift measured by satellite directly following the 2011-12 eruption at Cordon Caulle, Chile could have been caused by micro-scale melt migration from a crystal mush as opposed to recharge into the magma chamber from a deeper source. Crystal mushes are crystal rich structures filled with interstitial melt hypothesized to underlie compositionally evolved magmatic systems like Cordon Caulle. This melt segregation process changes how we consider surface uplift and its implications.
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    The rheology of particle-liquid suspensions, the shape and connectivity of vesicles in pyroclasts and implications for the Plinian eruption of basaltic magma
    (2015-12-01) Moitra, Pranabendu; Gonnermann, Helge M; Lee, Cin-Ty A; Lenardic, Adrian; Hirasaki, George J
    This thesis consists of three projects based on magma ascent dynamics during volcanic eruptions. In the first project, I quantified vesicle shapes in pyroclasts, from different styles of volcanic eruptions, using a dimensionless shape factor. I found that this shape factor can be related to a dimensionless Capillary number, estimated from coupled bubble growth and magma ascent modeling and thus, to the eruption styles. My second project dealt with understanding the effect of crystals on the rheological properties of magma from dynamically similar analog laboratory experiments. I found that the rheological properties of particulate suspensions depend on the applied shear rate and maximum packing fraction of a particulate system, which is a function of particle size- and shape-modality. Using empirical formulations, I showed that non-Newtonian rheology of crystalline magma may cause large changes in magma discharge rates for small changes in driving pressure gradient and/or crystal shape- and size-modality. In the third project, I measured permeability of pyroclasts from the Plinian style eruptions of basaltic magma at Mt. Etna (122 BCE) and Mt. Tarawera (1886) and found that the permeability of these pyroclasts are 1-2 orders of magnitude larger than that of the pyroclasts from Plinian style eruptions of silicic magmas. Using numerical modeling I found that the permeability thresholds are approximately at 35% of magma porosity and formulated the porosity-permeability relationships for pyroclasts from both the studied eruptions.
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    Widespread Disequilibrium of Phosphorus in Olivine
    (2020-04-09) Sharton-Bierig, Eytan; Lee, Cin-Ty A
    There are significant inconsistencies in the literature regarding the partition coefficient of phosphorus in olivine. This indicates that there may be a problem with the methods for determining this value. In this study, olivine phenocrysts from the Sequeiros Transform Zone were measured for phosphorus to determine the issues and constrain a more accurate value. The measured values range over several orders of magnitude. Estimates of phosphorus diffusivity in a basaltic melt are slower than some estimates of olivine growth rate, and this may mean that this spread is in some part due to kinetic effects during crystallization. As it is difficult to separate these contributions from the true equilibrium value, an alternative approach to constrain this value is needed. Using a statistical approach, we find a maximum value of D=0.027 and a minimum value of D=0.0033.