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Characterizing the Evolution of Slab Inputs

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Characterizing the Evolution of Slab Inputs University of South Florida Scholar Commons Graduate Theses and Dissertations Graduate School 3-23-2017 Characterizing the Evolution of Slab Inputs in the Earliest Stages of Subduction: Preliminary Evidence from the Fluid-Mobile Element (B, Cs, As, Li) Systematics of Izu-Bonin Boninitic Glasses Recovered During IODP Expedition 352 Keir Aavon Sanatan University of South Florida, [email protected] Follow this and additional works at: http://scholarcommons.usf.edu/etd Part of the Geochemistry Commons, and the Geology Commons Scholar Commons Citation Sanatan, Keir Aavon, "Characterizing the Evolution of Slab Inputs in the Earliest Stages of Subduction: Preliminary Evidence from the Fluid-Mobile Element (B, Cs, As, Li) Systematics of Izu-Bonin Boninitic Glasses Recovered During IODP Expedition 352" (2017). Graduate Theses and Dissertations. http://scholarcommons.usf.edu/etd/6755 This Thesis is brought to you for free and open access by the Graduate School at Scholar Commons. It has been accepted for inclusion in Graduate Theses and Dissertations by an authorized administrator of Scholar Commons. For more information, please contact [email protected]. Characterizing the Evolution of Slab Inputs in the Earliest Stages of Subduction: Preliminary Evidence from the Fluid-Mobile Element (B, Cs, As, Li) Systematics of Izu-Bonin Boninitic Glasses Recovered During IODP Expedition 352 by Keir Aavon Sanatan A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology School of Geosciences College of Arts and Sciences University of South Florida Major Professor: Jeffrey G. Ryan, Ph.D. Zachary D. Atlas, Ph.D. Aurelie Germa, Ph.D. Date of Approval: March 24, 2017 Keywords: Boninites, Fluid-mobile elements, Izu-Bonin-Mariana, Laser ablation, Subduction initiation, Volcanic glass Copyright © 2017, Keir Aavon Sanatan TABLE OF CONTENTS List of Tables .................................................................................................................................. ii List of Figures ................................................................................................................................ iii Abstract .......................................................................................................................................... iv Introduction ......................................................................................................................................1 Background and Geologic Setting ...................................................................................................7 Samples and Methods ....................................................................................................................10 EPMA Analysis .................................................................................................................11 Laser Ablation-ICP-MS Analysis ......................................................................................12 Results ............................................................................................................................................14 Discussion ......................................................................................................................................16 Boninite Within-Suite Characteristics – B, Cs, As and Tl systematics .............................16 Thallium systematics in Exp. 352 boninites: another FME? .................................18 Boninites from Serpentinites? ............................................................................................19 Global Arc Comparisons – B and Cs Systematics of IBM Boninites ...............................20 Li Systematics in Boninites ...............................................................................................22 Proposed IBM Subduction-Enrichment Model .................................................................25 Conclusions ...................................................................................................................................28 References ......................................................................................................................................30 Tables and Figures .........................................................................................................................39 i LIST OF TABLES Table 1a: Major element chemistry (in oxide wt%) of glass standards used at the Florida Center for Analytical Electron Microscopy ....................................................40 Table 1b: Analytical error of EPMA quality control standard USGS glass standard BHVO-1G .....................................................................................................41 Table 2a: Major element data in oxide wt% for boninitic glass samples analyzed at USF .........42 Table 2b: Fluid-mobile and light element data in ppm for boninitic glass samples analyzed at USF ...........................................................................................................43 Table 2c: REE data in ppm for boninitic glass samples analyzed at USF ...................................44 Table 2d: Trace element data in ppm for boninitic glass samples analyzed at USF ....................45 Table 2e: Analytic error in LA-ICP-MS quality control standard USGS glass BCR-1G ...........46 Table 3a: Major element data in oxide wt% for boninitic glass sample analyzed at the University of Iowa .......................................................................................................... ii LIST OF FIGURES Figure 1: Plots of MgO vs SiO2, TiO2 vs MgO and REE Masuda-Coryell REE diagram comparing boninitic glasses from this study to average Izu-Bonin boninites and Izu-Bonin and Mariana lavas ................................................................................48 Figure 2: Map of the IBM arc showing site of relevant ocean drilling expeditions ....................49 Figure 3: Plot of Cs/Th vs Ba/La comparing average Izu-Bonin bonintie and bonnite glasses from this study to average Izu-Bonin boninites and Izu-Bonin and Mariana lavas ...............................................................................................................50 Figure 4: Lithostratigraphic units of holes U1439C and U1442A ..............................................52 Figure 5: Plots of (a) B, (b) Cs and (c) As vs SiO2 of data collected from the IODP 352 glasses from this study .................................................................................................53 Figure 6: Plots of (a) B/La, (b) Cs/Th, and (c) As/Sm vs Ba/La of data collected from the IODP 352 glasses from this study ..........................................................................54 Figure 7: Plots of (a) Tl/La and (b) Cs/Tl vs Ba/La of data collected from the IODP 352 glasses from this study .................................................................................................55 Figure 8: Primitive mantle normalized (Sun and McDonough 2004) spidergram of IODP Expedition 352 boninite glass samples from this study as compared to Mariana forearc serpentinites from ODP Leg 125 Site 780 .......................................................56 Figure 9: Plots of (a) B/La an (b) Cs/Th vs Ba/La comparing the data obtained for the IOPD 352 glass samples from this study to whole rock data from other global arc suites.......................................................................................................................57 Figure 10: Plots of (a) Li vs SiO2 and (b) Li vs MgO of the data collected from the IODP 352 glasses from this study ................................................................................58 Figure 11: (a) Plot of Li/Yb vs Dy/Yb and (b) Plot of K/Li vs La/Yb of IODP 352 glasses from this study .................................................................................................59 Figure 12: Plot of Li/Yb vs Ba/La of IODP 352 glasses from this study ......................................60 Figure 13: Conceptual model of IBM arc evolution ....................................................................61 iii ABSTRACT Fluid-mobile elements (FMEs) such as B, Cs, As, Li and Tl can mobilize readily under low P-T conditions (0.2-0.5 GPa). This makes them effective geochemical tracers that can be used as a way of tracking fluid-rock exchanges at the shallow depths encountered in the earliest stages of subduction. The Izu-Bonin-Mariana (IBM) subduction system is unique in that it preserves a record of the sequences produced from the onset of subduction through the development of arc magmatism. International Ocean Discovery Program (IODP) Expedition 352 recovered >800m of boninite core material from the earliest IBM magmatic events. Select boninitic glasses from these IODP 352 cores, found mostly as selvages on the rinds of pillow lavas and as clasts within hyaloclastites, were examined via EPMA and laser ablation ICP-MS techniques. The boninite glasses analyzed were separated into two categories – low-silica boninite (LSB) and high-silica boninites (HSB), based on the bulk chemistry and mineralogy of the lithostratigraphic locations from which the glass samples occur in the drill core. LSB are the earlier erupted boninite series, which show both greater variation in extent of differentiation and reflect less depleted mantle sources than HSB. Boron concentrations in the Expedition 352 boninite glasses analyzed range from 0.08 to 12.91 ppm, arsenic contents
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