UUnniivveerrssiittyy ooff SSoouutthh CCaarroolliinnaa SScchhoollaarr CCoommmmoonnss Theses and Dissertations 1-1-2013 VVoollccaanniicc aanndd TTeeccttoonniicc PPrroocceesssseess AAlloonngg AAnnoommaalloouuss MMiidd--OOcceeaann RRiiddggeess Julia Kathryn Howell University of South Carolina Follow this and additional works at: https://scholarcommons.sc.edu/etd Part of the Geology Commons RReeccoommmmeennddeedd CCiittaattiioonn Howell, J. K.(2013). Volcanic and Tectonic Processes Along Anomalous Mid-Ocean Ridges. (Doctoral dissertation). Retrieved from https://scholarcommons.sc.edu/etd/2312 This Open Access Dissertation is brought to you by Scholar Commons. It has been accepted for inclusion in Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. VOLCANIC AND TECTONIC PROCESSES ALONG ANOMALOUS MID-OCEAN RIDGES by Julia Kathryn Howell Bachelor of Science North Carolina State University, 2008 _______________________________________________ Submitted in Partial Fulfillment of the Requirements For the Degree of Doctor of Philosophy in Geological Sciences College of Arts and Sciences University of South Carolina 2013 Accepted by: Scott M. White, Major Professor Michael Bizimis, Committee Member David Barbeau, Committee Member DelWayne Bohnenstiehl, Committee Member Lacy Ford, Vice Provost and Dean of Graduate Studies © Copyright by Julia Kathryn Howell, 2013 All Rights Reserved. ii DEDICATION To my family, who always believed I could do anything; to my mother, because I am just like her; and to my father, who made me wait and see. iii ACKNOWLEDGEMENTS This dissertation would not have been possible without guidance and advice from Dr. Scott M. White, Dr. DelWayne R. Bohnenstiehl, Dr. Michael Bizimis, Dr. Mark Behn, and Dr. David Barbeau. iv ABSTRACT The morphological and structural characteristics of the global spreading ridge system are systematically related to spreading rate and magma supply (e.g. Macdonald, 1982). Because intermediate spreading-rate ridges (ISRs) spreading between 60 and 80 mm/yr have characteristics of both fast and slow spreading ridges, they are ideal environments to study the differences controlling upper crustal accretion. We examine the distribution of seamounts along spreading ridges to understand the relationship between seamount volcanism and axial morphology along four ISRs: the Juan de Fuca Ridge (JdFR), the Galápagos Spreading Centers (GSC), the Southeast Indian Ridge (SEIR), and the Eastern Lau Spreading Centers (ELSC). Before determining the distribution of volcanoes on the seafloor, the Modified Basal Outlining Algorithm (MBOA) developed by Bohnenstiehl et al. (2012) is assessed for its accuracy in picking volcanic edifices relative to a traditional field-based geologic mapping approach at the Springerville Volcanic Field, Arizona. There, MBOA is able to closely match the geologic map, under-predicting height and area by 4% and over-predicting volume by 13%. Applying MBOA to determine the seamount abundance, volume and spatial distribution along the ISRs indicate that (1) seamounts do not form at the ends of segments along the JdFR, GSC or ELSC, but do form at the ends of segments along the SEIR, (2) a systematic relationship exists between axial morphology and ridge migration in the hotspot reference frame along the SEIR, and (3) segments offset in the direction of ridge migration have axial highs along the leading segment end and axial valleys along v the trailing segment end. Given that ridge migration oblique to spreading direction causes enhanced melting beneath the leading segment end (Katz et al., 2004), we attempt to understand the formation of faults when the near-field spreading direction is oblique to the far-field stretching direction (i.e., the direction plates are pulled apart). Three dimensional finite-element modeling of an idealized MOR indicates that faults slip in a direction halfway between the spreading and stretching directions outside of the axial graben. Inside the axial graben, faults slip in a direction approaching the stretching direction. This indicates simply pulling the lithosphere causes the orientation of volcanic and tectonic structures to change without changing the underlying structure of the upwelling asthenosphere. vi TABLE OF CONTENTS Dedication ......................................................................................................................... .iii Acknowledgements ............................................................................................................ iv Abstract ...............................................................................................................................v List of Tables ................................................................................................................... viii List of Figures .................................................................................................................... ix Chapter 1: Introduction ........................................................................................................1 Chapter 2: A Modified Basal Outlining Algorithm for Identifying Topographic Highs in Gridded Elevation Data Applied to Springerville Volcanic Field ................................................................................17 Chapter 3: Seamount abundance, volume and spatial distribution along three hotspot-influenced intermediate spreading-rate ridges .......................39 Chapter 4: Seamount formation along the Eastern Lau Spreading Center ........................84 Chapter 5: 3D Geodynamic Models of Lithospheric Stress Along Oblique Spreading Ridges ...................................................................................105 Chapter 6: Conclusions ....................................................................................................124 References ........................................................................................................................127 vii LIST OF TABLES Table 3.1 Distribution of seamounts along segment ..........................................................82 Table 3.2 Seamount statistics .............................................................................................83 Table 5.1 List of symbols.................................................................................................113 Table 5.2 Table of constants ............................................................................................114 viii LIST OF FIGURES Figure 1.1 Global Map of the mid-ocean ridge system .......................................................9 Figure 1.2 Axial morphology of the East Pacific Rise ......................................................10 Figure 1.3 Across axis depth profile of the East Pacific Rise ............................................11 Figure 1.4 Melt lens location along fast spreading ridges .................................................12 Figure 1.5 Axial morphology of the Mid-Atlantic Ridge ..................................................13 Figure 1.6 Across axis depth profile of the Mid-Atlantic Ridge .......................................14 Figure 1.7 Expected magma location along slow spreading ridges ...................................15 Figure 1.8 Schematic of a migrating ridge.........................................................................16 Figure 2.1 Regional map of the Springerville Volcanic Field ...........................................32 Figure 2.2 Comparison of resolution and contour interval ................................................33 Figure 2.3 Quantified comparison of methodology ...........................................................34 Figure 2.4 Differences in methodology at low resolutions ................................................35 Figure 2.5 Differences in methodology at different contour intervals ...............................36 Figure 2.6 Sensitivity of the height/radius ratio to methodology ......................................37 Figure 2.7 Height-frequency distribution for each methodology ......................................38 Figure 3.1 Global map of the mid-ocean ridge system ......................................................62 Figure 3.2 Regional map of the Juan de Fuca Ridge .........................................................63 Figure 3.3 Regional map of the Galápagos Spreading Centers .........................................64 Figure 3.4 Regional map of the Southeast Indian Ridge ...................................................65 ix