Date of Award

1-1-2011

Document Type

Campus Access Thesis

Department

Earth and Ocean Sciences

Sub-Department

Geology

First Advisor

Scott M White

Abstract

Submarine volcanism at mid-ocean ridges (MORs) comprises the majority of global magmatism and produces the quantum units of the upper oceanic crust, which covers over 70% of Earth's surface. Despite being one of our planet's most prolific and ubiquitous processes, only two deep seafloor eruptions have ever been directly observed, therefore eruption dynamics and emplacement kinematics must be inferred from the spatial arrangement and morphological and physical properties of eruptive products. However, few studies have investigated MORs at the scale of individual eruptions; this lack of observations is a critical gap in our conceptual understanding of crustal genesis at MORs. This dissertation seeks to advance our knowledge of MOR volcanic processes through fieldwork and novel analytical experiments.

I begin by reviewing previous geological investigations of the deep ocean floor and introducing the concept of computer-aided geoclassification as an important aid to traditional field-based submarine geologic mapping and sampling methods. This type of methodology is then demonstrated in Chapter 2, in which submersible-based geologic fieldwork and high-resolution sonar data are integrated with a geoclassification algorithm to produce detailed volcanological maps of lava flow fields at the Galápagos Spreading Center (GSC). The maps are used to provide quantitative estimates of the abundance and spatial distribution of lava flow morphologies, which are used as a proxy for comparing average effusion rates within two study sites at the GSC with contrasting magma supply rates.

Next, to further explore the controls on submarine lava flow morphology, I use digital petrography to determine the crystallinity and bulk viscosity of basaltic lava flow samples from the GSC. I show that bulk viscosity can vary significantly within lava flow fields and with relatively small variations in crystallinity. Using quantitative textural analysis techniques, I find distinct differences in crystal size and shape distribution between lava morphology types. I also compare the characteristics of lava flow samples from lower- and higher-magma-supply study sites at the GSC.

In the final chapter, I examine the architecture of Niños, a single lava flow field at the GSC near 92°W. Using high-precision sonar bathymetry, a spatial and stratigraphic progression of volcanic morphofacies is identified, each with distinctive patterns of lava flow morphology and volcanic structures. Collectively, the progression of facies is the geomorphological expression of flow localization processes. Individually, each facies suggests specific vent geometry and emplacement kinematics, providing a conceptual framework within which to make inferences about the construction of lava flow fields elsewhere at the GSC and at other MORs.

Rights

© 2011, James T. McClinton

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