Magmatic Differentiation in Arc and Mid Ocean Ridge Settings

• Main Author: Lewis, Madeline Janine
• Format: Thesis
• Language: English
• Published: California Institute of Technology 2021
• Subjects: Magma; differentiation; geochronology; magmatic arc; volcano; iron formation; Geochemistry; FOS Earth and related environmental sciences; geochemistry; mid-ocean ridge; petrology; Antarctic; Pacific; Antarc*
• Online Access: https://dx.doi.org/10.7907/a1ky-ab66; https://resolver.caltech.edu/CaltechTHESIS:06022021-034345855

The compositional variation of igneous rocks and construction of Earth's crust is the result of magmatic differentiation -- crystallization, melting, and assimilation mechanisms that cause 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. Here, 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.