Magmatic processes play a central role in the thermal, chemical, and hydrologic evolution of rocky planets by linking deep planetary interiors to their crusts and surface environments. This thesis integrates igneous and metamorphic petrology, stable isotope geochemistry, and thermodynamic modeling to investigate how magmatic rocks record the coupled evolution of planetary interiors and surface environments on both Earth and Mars. On Earth, I focus on sediment-derived magmas\u2014strongly peraluminous granites (SPGs) and associated pelitic migmatites\u2014which form by partial melting of metasedimentary crust and preserve geochemical signatures inherited from surface-processed materials. On Mars, I focus on primary and weakly evolved mafic magmas, which provide direct constraints on mantle temperatures, crustal differentiation, and the role of magmatism in sustaining subsurface water.
\r\n\r\nThe first part of the thesis examines how sedimentary signatures are transferred into granitic magmas during crustal anatexis and what these signatures reveal about Earth\u2019s long-term surface evolution. Iron isotope measurements and petrological modeling of the Neoarchean Ghost Lake Batholith show that partial melting largely homogenizes extreme sedimentary isotopic heterogeneity while preserving a resolvable record of bulk source composition, establishing SPGs as robust archives of secular iron isotope evolution in siliciclastic sediments. Building on this framework, triple-oxygen-isotope analyses of garnet in sediment-derived granites and migmatites are used to reconstruct weathering temperatures and meteoric water compositions from the Neoarchean to the Mesozoic, revealing discrete climate regimes linked to atmospheric oxidation, glaciation, and supercontinent cycles and demonstrating that sediment-derived magmas provide a lithology-integrated archive of Earth\u2019s surface environments.
\r\n\r\nThe second part of the thesis addresses how Martian magmatism records the thermal evolution of a stagnant-lid planet and its interaction with the hydrosphere. I introduce PRIMARSMELT, a new petrological modeling tool for reconstructing primary magma compositions and mantle potential temperatures from Martian meteorite and rover data. Application of this approach indicates that Martian mantle temperatures have remained nearly constant\u2014or may have increased\u2014through time, consistent with inefficient heat loss in the absence of plate tectonics. I further show that, although Martian magmas inevitably generate water-rich fluids during differentiation, fluid\u2013rock reactions rapidly seal permeability, implying that any present-day liquid water in the Martian crust must be continuously supplied by active magmatic degassing. Finally, mineral-scale observations from the Perseverance rover in Jezero crater demonstrate that ultramafic cumulates of the S\u00e9\u00edtah formation and basaltic lavas of the M\u00e1az formation formed within the same magmatic system, linking intrusive and extrusive processes and illustrating how crystal accumulation and differentiation generate lithologic diversity in the Martian crust.
\r\n \r\nTogether, these studies show how magmatic processes record the thermal evolution of planetary interiors and mediate their interactions with crustal and hydrologic systems, providing a comparative framework for understanding how rocky planets build crusts, cycle volatiles, and evolve toward\u2014or away from\u2014habitability.
", "doi": "10.7907/p2m8-p097", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:18768", "collection": "thesis", "collection_id": "18768", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022026-045136630", "type": "thesis", "title": "Ocean-Mantle Interactions Through Earth History", "author": [ { "family_name": "Bednarick", "given_name": "Amanda Lee", "orcid": "0000-0001-6813-9082", "clpid": "Bednarick-Amanda-Lee" } ], "thesis_advisor": [ { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0001-5332-8278", "clpid": "Bucholz-C-E" } ], "thesis_committee": [ { "family_name": "Eiler", "given_name": "John M.", "orcid": "0000-0001-5768-7593", "clpid": "Eiler-J-M" }, { "family_name": "Stolper", "given_name": "Daniel Aaron", "orcid": "0000-0003-3299-3177", "clpid": "Stolper-Daniel-Aaron" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Chemical and isotopic exchange between seawater and oceanic crust is a fundamental mechanism by which Earth\u2019s surface and interior interact. This exchange is fundamental to understanding Earth\u2019s chemical and volatile cycling, climate regulation, continental growth, and habitability. Strontium isotopes (\u2078\u2077Sr/\u2078\u2076Sr) are a powerful tracer of this process because the ocean and mantle have distinct isotopic signatures that are reasonably well-constrained through Earth history. The research chapters of the thesis investigate how ocean-mantle interactions have operated on long timescales, centering on hydrothermal alteration at spreading centers as the locus of seawater-seafloor Sr isotopic exchange. Ophiolites and island arcs serve as archives of and windows into ancient, seawater-altered oceanic crust.
\r\n\r\nIn Chapter II, we demonstrate that island arc \u2078\u2077Sr/\u2078\u2076Sr has covaried with seawater Sr isotope composition and concentration over the past two billion years. The observation is consistent with modern understanding of geochemical cycling at subduction zones \u2013 that seawater chemistry exerts a first-order control on the composition of the subducting oceanic crust, which island arc magmatic rocks inherit \u2013 but it is a novel result to show that \u2078\u2077Sr/\u2078\u2076Sr enrichment is a persistent feature of island arcs. The mechanism by which seawater chemistry affects oceanic crust is via large-scale fluid circulation of seawater-derived fluids through nascent seafloor at hydrothermal systems. The result of the interactions at the interface of seawater and seafloor is an isotopic shift in oceanic crust towards more radiogenic, seawater-like \u2078\u2077Sr/\u2078\u2076Sr.
\r\n\r\nChapter III tests this framework by probing the record of seawater-altered oceanic crust directly, using ophiolites. A compilation of ophiolitic dike samples aged 0-750 Ma suggests that the magnitude of seawater-seafloor Sr isotopic exchange has varied systematically through the Phanerozoic and Neoproterozoic in concert with seawater Sr isotopic composition and concentration, supporting the hypothesis that seawater chemistry has been a first-order control on hydrothermal alteration intensity throughout this interval. Given the purported connection between seawater chemistry and Sr isotopic patterns in ophiolites, we hypothesized that ancient ophiolites may lend insights into seawater chemistry and hydrothermal alteration dynamics during periods of Earth history during which we have few constraints on geochemical cycling and climate feedbacks. To test this, we present \u2078\u2077Sr/\u2078\u2076Sr data through two sections of Precambrian altered oceanic crust \u2013 the 1.7 Ga Payson ophiolite and the 2.0 Ga Purtuniq ophiolite \u2013 and find that the structure of the ancient ophiolite \u2078\u2077Sr/\u2078\u2076Sr data is largely similar to that from modern and Cretaceous oceanic crust and ophiolites. We interpret this to mean modern-style hydrothermal alteration was ongoing by the Paleoproterozoic.
\r\n\r\nChapters IV and V expand on this premise, employing complementary geochemical systems to probe seawater-seafloor interactions from different angles. Oxygen isotopes through the 1.7 Ga Payson ophiolite independently constrain the section as representative of seawater-altered oceanic crust. This further supports the idea that modern-style hydrothermal alteration was ongoing by the Paleoproterozoic, lending insight into weathering regimes at the time. Fe\u00b3\u207a/\u03a3Fe data from both ophiolites tentatively suggest that hydrothermal alteration was driving modest oxidation in the extrusive units of the 1.7 Ga Payson ophiolite relative to the least-altered intrusive units, but not in the 2.0 Ga Purtuniq ophiolite.
\r\n\r\nChapter VI uses unaltered ophiolitic gabbros and ultramafic rocks to construct an empirical record of depleted mantle \u2078\u2077Sr/\u2078\u2076Sr for the Phanerozoic. The results suggest that the isotopically heterogeneity in the depleted mantle that we recognize today has been long-lived, persisting at least as far back as 500 million years.
\r\n\r\nTogether, these findings indicate that the coupling between surface ocean chemistry and the geochemistry of oceanic crust has been operating since at least the Paleoproterozoic. These findings are important for informing how the geochemistry and Earth history communities conceptualize ancient ocean and mantle conditions, geochemical cycling, weathering feedbacks, and surface-mantle connectivity.
", "doi": "10.7907/8f50-kd29", "publication_date": "2026", "thesis_type": "phd", "thesis_year": "2026" }, { "id": "thesis:17353", "collection": "thesis", "collection_id": "17353", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022025-035505104", "primary_object_url": { "basename": "RyanDavis_Juliet_Thesis2025.pdf", "content": "final", "filesize": 14710775, "license": "other", "mime_type": "application/pdf", "url": "/17353/3/RyanDavis_Juliet_Thesis2025.pdf", "version": "v5.0.0" }, "type": "thesis", "title": "Crystalline Records of Mafic Arc Magmas Across the Sierra Nevada Batholith, California", "author": [ { "family_name": "Ryan-Davis", "given_name": "Juliet Rose", "orcid": "0000-0001-7048-5937", "clpid": "Ryan-Davis-Juliet-Rose" } ], "thesis_advisor": [ { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" } ], "thesis_committee": [ { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Eiler", "given_name": "John M.", "orcid": "0000-0001-5768-7593", "clpid": "Eiler-J-M" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Our planet Earth is unique among the rocky planets of the solar system in having compositionally evolved continental crust\u2014the reason for life as we know it. Processes that create continental crust occur at subduction zones where magmas differentiate, evolving from primary mantle-derived basalt to produce a diverse range of compositions that erupt at arc volcanoes and comprise the bulk of the continental crust. Many processes for differentiation have been proposed, yet, recognizing and evaluating the role of pre-existing crust in these processes remains challenging.
\r\n\r\nThis thesis includes two studies of mafic intrusions in the Sierra Nevada batholith\u2014the well-studied Mesozoic continental arc of the western North American Cordillera. The studies are grounded in field and petrographic observations. By targeting the intrusive record, they document the time-integrated effects of mafic magmatism over tens of millions of years within a volcanic arc.
\r\n\r\nChapter 2 is a petrologic study of the most primitive intrusive rocks of the batholith, exposed in the Emigrant Gap complex. The complex ranges compositionally from ultramafic cumulates to intermediate granodiorite. The petrology, geochemistry and field relationships of these plutonic rocks reveal that\u2014in addition to crystallization\u2014open-system processes (melt-mush reactions and hybridization between the mafic products and a crustally contaminated felsic magma) produced the distinctive geochemical and petrologic trends of the complex.
\r\n\r\nChapters 3 and 4 represent a broad study of mafic intrusions within a 250 km by 100 km swath of the central Sierra Nevada (37\u00b10.5\u00b0N latitude). This regional perspective on mafic magmatism spans ~110 million years and crosses several tectonically-assembled belts, each with distinctive geology. The two chapters document systematic differences in field relationships and geochemistry of the mafic intrusions that vary by geologic belt, as the mafic magmas interacted with heterogeneous crust. Chapter 3 presents field relationships, ages, and major and trace element chemistry. Chapter 4 presents isotopic compositions (O, Hf, Sr, and Nd), revealing that contamination of mafic magmas by ~10\u201320% assimilation of the local crustal column is inevitable, and that it occurs early during differentiation.
", "doi": "10.7907/y34m-jj74", "publication_date": "2025", "thesis_type": "phd", "thesis_year": "2025" }, { "id": "thesis:16423", "collection": "thesis", "collection_id": "16423", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:05242024-181307541", "primary_object_url": { "basename": "Thesis_EmmaSofiaSosa_2024.pdf", "content": "final", "filesize": 47888177, "license": "other", "mime_type": "application/pdf", "url": "/16423/1/Thesis_EmmaSofiaSosa_2024.pdf", "version": "v6.0.0" }, "type": "thesis", "title": "Composition, Structure, and Formation of the Lower Crust in Continental and Oceanic Arc Settings: Insights from the Xenolith Record", "author": [ { "family_name": "Sosa", "given_name": "Emma Sofia", "orcid": "0000-0002-1765-6191", "clpid": "Sosa-Emma-Sofia" } ], "thesis_advisor": [ { "family_name": "Bucholz", "given_name": "Claire", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" } ], "thesis_committee": [ { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" }, { "family_name": "Tissot", "given_name": "Fran\u00e7ois L. H.", "orcid": "0000-0001-6622-2907", "clpid": "Tissot-F-L-H" }, { "family_name": "Eiler", "given_name": "John M.", "orcid": "0000-0001-5768-7593", "clpid": "Eiler-J-M" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The compositional variability of lavas erupted in subduction zone settings results from a multitude of deep crustal processes acting in concert, reflecting variations among arcs in source rock composition, water content, oxidation state (fO2), temperature, pressure, and crystallization sequence across arcs. Lower to mid-crustal xenoliths\u2014deeply sourced rock fragments entrained and brought to the surface by ascending melts\u2014provide a robust record of the chemistry and structure of their inaccessible source regions. This thesis combines a variety of laboratory techniques and modeling approaches to explore the origins of two xenolith suites from vastly different arc settings: the oceanic Aleutian Arc off the coast of Alaska and the continental Andean Arc in Colombia. While all samples are fully characterized in terms of their petrography and the major and trace element chemistry (of both minerals and whole-rock), special attention is given to stable Fe isotope ratios, which are particularly sensitive to the fractionation of important Fe-bearing minerals like olivine, magnetite, amphibole, and garnet. \t\r\n In the first chapter, we document the major and trace element compositions of 39 previously undescribed xenoliths from the Mt. Moffett and Mt. Adagdak volcanic centers on Adak Island, Central Aleutians. This data is then used to evaluate the P-T-fO2-H2O conditions under which the cumulates formed and interrogate the nature of their parental melts. The second chapter builds upon this first study, presenting Fe isotope data of whole-rock powders and mineral separates (spinel, clinopyroxene, olivine, amphibole, and magnetite) from the Adagdak xenoliths. Our data show that the Adak crust is stratified in terms of Fe isotopes, with an isotopically light lower-crust and an isotopically heavy middle to upper-crust. The implications of this compositional structure and its relation to the evolution of Adagdak magmas is then explored through mass-balance fractional crystallization modeling. In the final chapter, we apply the same methods used in the first two chapters to characterize a suite of lower to mid-crustal xenoliths from the Mercaderes region of Colombia in the Central Andean Cordillera. In contrast to Adagdak, the Mercaderes samples show a nearly constant whole-rock Fe isotope composition throughout our ~50 km crustal section. Through thermodynamic modeling, we show that the most likely explanation for this data is that the Mercaderes suite represents a prograde metamorphic sequence", "doi": "10.7907/2arj-v665", "publication_date": "2024", "thesis_type": "phd", "thesis_year": "2024" }, { "id": "thesis:14228", "collection": "thesis", "collection_id": "14228", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022021-013516525", "primary_object_url": { "basename": "Biasi Thesis.pdf", "content": "final", "filesize": 19117516, "license": "other", "mime_type": "application/pdf", "url": "/14228/1/Biasi Thesis.pdf", "version": "v4.0.0" }, "type": "thesis", "title": "Paleomagnetism and Geochemistry of Basalts in the North American Cordillera, Davis Strait, and Antarctica", "author": [ { "family_name": "Biasi", "given_name": "Joseph Anthony", "orcid": "0000-0003-1196-7877", "clpid": "Biasi-Joseph-Anthony" } ], "thesis_advisor": [ { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" }, { "family_name": "Kirschvink", "given_name": "Joseph L.", "orcid": "0000-0001-9486-6689", "clpid": "Kirschvink-J-L" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "Chapter 1 is an introduction to the thesis and contains a brief summary on how the chapters relate to each other. In Chapter 2, we present new whole-rock geochemical data from the Brooks Range Ophiolite (BRO) together with new mineral chemistry data from the BRO, South Sandwich forearc, Izu-Bonin forearc, and Hess Deep. In Chapter 3, we use a combination of paleomagnetic data and thermal modeling to create a magnetic geothermometer (MGT) that can constrain the active transport lifetime of magmatic conduits and igneous intrusions. In Chapter 4, we present new stratigraphic and paleomagnetic data from Paleocene flood basalts on Baffin Island. In Chapter 5, we present new paleomagnetic and paleointensity data from the James Ross Island volcanic group, located on the Antarctic Peninsula.
", "doi": "10.7907/hbs7-aw47", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" }, { "id": "thesis:14229", "collection": "thesis", "collection_id": "14229", "cite_using_url": "https://resolver.caltech.edu/CaltechTHESIS:06022021-034345855", "type": "thesis", "title": "Magmatic Differentiation in Arc and Mid Ocean Ridge Settings", "author": [ { "family_name": "Lewis", "given_name": "Madeline Janine", "orcid": "0000-0001-7968-2822", "clpid": "Lewis-Madeline-Janine" } ], "thesis_advisor": [ { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" }, { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" } ], "thesis_committee": [ { "family_name": "Rossman", "given_name": "George Robert", "orcid": "0000-0002-4571-6884", "clpid": "Rossman-G-R" }, { "family_name": "Fischer", "given_name": "Woodward W.", "orcid": "0000-0002-8836-3054", "clpid": "Fischer-W-W" }, { "family_name": "Stolper", "given_name": "Edward M.", "orcid": "0000-0001-8008-8804", "clpid": "Stolper-E-M" }, { "family_name": "Bucholz", "given_name": "Claire E.", "orcid": "0000-0003-3252-7109", "clpid": "Bucholz-C-E" }, { "family_name": "Asimow", "given_name": "Paul David", "orcid": "0000-0001-6025-8925", "clpid": "Asimow-P-D" } ], "local_group": [ { "literal": "div_gps" } ], "abstract": "The compositional variation of igneous rocks and construction of Earth's crust is the result of magmatic differentiation -- crystallization, melting, and assimilation mechanisms that\r\ncause the composition of magmas to change over time. This thesis investigates magma generation and evolution at both convergent and divergent plate boundaries. The resulting magmatic arcs and mid-ocean ridges create the vast majority of Earth's crust, though the details of crustal construction and the specific processes that generate the observed magmatic and volcanic products are complex. Accordingly, this work uses the geochemical signatures encoded in rocks and minerals to explain magmatic differentiation histories in multiple tectonic settings.
\r\n\r\nHere, I present five main studies that utilize field and textural observations, geochemical analyses, and computational modeling to investigate the compositional structure of the crust beneath magmatic arcs and mid-ocean ridges. In addition, this work explores the pyroclastic and sedimentary products dispersed by magmatically heated hydrothermal fluids in submarine environments. Chapters 2 and 3 investigate the crystallization histories of mafic intrusions in the eastern-central Sierra Nevada batholith paleo-continental arc, California. This work has implications for the compositional and temporal generation of both mafic and evolved magmas throughout the batholith and in other continental arcs. Chapters 4 and 5 explore records of submarine volcanic ash deposits associated with explosive mid-ocean ridge eruptions from the East Pacific Rise and Pacific-Antarctic Ridge, as well as the effects that sea level change has on melting of the mantle, eruption styles, and the compositional evolution of mid-ocean ridge magmas. Chapter 6 examines the mineral hosting of rare earth elements (REEs) in the Wadi Karim banded iron formation, and the implications of element mobility on interpretations based on REE abundances.
", "doi": "10.7907/a1ky-ab66", "publication_date": "2021", "thesis_type": "phd", "thesis_year": "2021" } ]