京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20925号 / 理博第4377号 / 新制||理||1628(附属図書館) / 京都大学大学院理学研究科地球惑星科学専攻 / (主査)教授 田上 高広, 教授 下林 典正, 准教授 河上 哲生 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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Thesis advisor: Ethan Baxter / Thesis advisor: Mark Behn / Subduction zones are areas of significant mass transfer between Earth’s crust and mantle. The dehydration of water-rich minerals such as serpentinite and lawsonite introduces water and volatiles into the subduction interface, that then travel to the mantle wedge above. The chemical composition, speciation, and redox effect of these fluids carry important implications for arc volcanism and the mobility of economically significant elements. This study uses Fe and Zn isotopic variation in eclogite-breccias from the Monviso ophiolite, combined with Sm-Nd garnet geochronology, to study the composition and redox effects of fluids that were produced during eclogite and blueschist facies metamorphism, and the timescales over which the brecciation and fluid flux events happened. Fe and Zn isotopic measurements were made on a series of four breccia matrix generations (M1-M4), generated during the progressive brecciation of the original Fe-Ti gabbros and the influx of both internally and externally derived fluids. The ∂56Fe and ∂66Zn data display a bi-modal distribution, with early matrix crystallization (M1-3) imparting progressively lighter ∂66Zn values while the ∂56Fe remains relatively unchanged. The last stage of metasomatic rind formation (M4) is associated with a decrease in both Fe and Zn isotopic values and a particularly significant shift in the Fe isotopes. This distribution suggests that early brecciation (M1-3) resulted from small-scale internal fluid flow that did not have a measurable effect on the isotopic composition and redox state of the system. By contrast, late metasomatic rind formation (M4) was facilitated by the flow of large amounts of external fluids with a strongly negative Fe and Zn isotope signature that affected the redox state of the mafic slab and may be responsible for transferring oxidized material into the mantle wedge. Dating of the M4 matrix generation yielded an age of 41.31± 0.60 Ma. A compilation of age data from Monviso suggests peak metamorphism and initial brecciation (M1 formation) likely occurred at ~45 Ma, the formation of the M4 matrix representing the end of eclogite-facies retrogression and brecciation at ~41 Ma, and final blueschist and greenschist retrogression at ~38-35Ma, yielding timescale of ~4Ma for the entire history of brecciation and fluid flux associated with the Monviso eclogite breccias. / Thesis (MS) — Boston College, 2022. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

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<p>The kinematics and associated deformation of upper crust in fossil and active convergent tectonic settings require different methods of study. In this thesis, I analyzed an example of a fossil convergent setting, the formation of the eastern portion of Paleoproterozoic Sudbury Basin, Ontario, and an example of an active convergent plate interface represented by the ongoing subduction along the Hellenic Arc at Rhodes, Greece. In Sudbury, using paleomagnetic remanence directions and Matachewan dyke orientations, I constrain the magnitudes of rotation associated with the formation of the NE-lobe, a tight secondary fold of the Sudbury Basin, as well as localize the fold axis and magnitude of rotation along the West Bay Anticline, a hitherto unknown fold of the Basin.</p> <p>For the Island of Rhodes, I corroborate the existence of two phases of Plio-Pleistocene or younger deformation including providing their principal strain axis orientations from a fault-slip analysis. In addition, I estimate the magnitude of slip from faults to generate respective incremental strain ellipses of the two deformation phases for the Island. The first phase is characterized by vertical shortening (ŝ₃) and N-S extension (ŝ₁) with associated normal faulting while the second phase is characterized by N-S shortening (ŝ₃) and E-W extension (ŝ₁) associated with strike-slip faulting.</p> / Master of Science (MSc)