The University of Southern Mississippi The Aquila Digital Community Master's Theses Spring 5-2021 Structural Re-orientation of Magmatic Fabrics and Layering in the Lower Oceanic Crust: Hole GT1, Wadi Tayin Massif, Samail Ophiolite Justin Guillot Follow this and additional works at: https://aquila.edu/masters_theses Part of the Geology Commons Recommended Citation Guillot, Justin, "Structural Re-orientation of Magmatic Fabrics and Layering in the Lower Oceanic Crust: Hole GT1, Wadi Tayin Massif, Samail Ophiolite" (2021).edu/masters_theses/802 This Masters Thesis is brought to you for free and open access by The Aquila Digital Community. It has been accepted for inclusion in Master's Theses by an authorized administrator of The Aquila Digital Community. For more information, please contact Joshua. STRUCTURAL RE-ORIENTATION OF MAGMATIC FABRICS AND LAYERING IN THE LOWER OCEANIC CRUST: HOLE GT1, WADI TAYIN MASSIF, SAMAIL OPHIOLITE by Justin Guillot A Thesis Submitted to the Graduate School, the College of Arts and Sciences and the School of Biological, Environmental, and Earth Sciences at The University of Southern Mississippi in Partial Fulfillment of the Requirements for the Degree of Master of Science Approved by: Dr.
Jeremy Deans, Committee Chair Dr. Mark Puckett Dr. Franklin Heitmuller May 2021 COPYRIGHT BY Justin Guillot 2021 Published by the Graduate School ABSTRACT This thesis aims to re-orient borehole images of layered gabbros sampled beneath Hole GT1 in the Wadi Tayin massif of the Oman ophiolite by the Oman Drilling Project to better constrain models of crustal accretion. The gabbro glacier model proposes that crystallized basalt flows down and away from the crystallization site to form the lower crust while the sheeted sill model proposes that basaltic melt crystallizes at multiple levels in the crust through sills.
Hole GT1 provides an unprecedented 400 m, 100% recovery, look at the lower oceanic crust. Cores lose their geographic orientation when drilled, requiring use of the programs like Techlog to match core observations with borehole images oriented relative to north to re-orient the core. Layering is more common throughout the borehole overall but becomes sparse past 250 meters below surface (mbs) whereas magmatic fabrics become more frequent past 300 mbs. Most magmatic fabrics share an average strike of 060 while layering measurements strike close to 355.
Both undergo an orientation shift from NE to SW past 300 mbs. The non-systematic distribution of MFs and layering observed below Hole GT1 matches more closely with the sheeted sill model and the idea of melt intruding an upper crystal mush reservoir as a mixing bowl that develops layering and fabrics if enough melt is present for further intrusion. The variance in dip azimuth downhole implies that these features formed through local processes, which supports geochemical evidence that the lower crust forms in an open system through multiple re-intrusions. ii ACKNOWLEDGMENTS I hereby express my deepest gratitude to my Committee Chair Dr.
Jeremy Deans for their support, advice, and patience throughout the past few years. It is through the help of their written comments, experience, and sincere words of encouragement that I was able to complete this thesis. I would also like to thank Dr. Franklin Heitmuller and Dr.
Mark Puckett for taking the time to be members of my committee in addition to being great teachers who have contributed to my overall growth as a geologist. iii TABLE OF CONTENTS ABSTRACT. iii LIST OF TABLES. vii LIST OF ILLUSTRATIONS.
viii LIST OF ABBREVIATIONS. xiv CHAPTER I - INTRODUCTION. 7 CHAPTER II –METHODS .1 Materials and Methods. 10 CHAPTER III – RESULTS .1 Depth Plots and Histograms.2 Dip Azimuth vs.
Depth Plot: Layering .3 Dip Azimuth vs. Depth Plot: All Data .4 Dip Azimuth Vs. Depth Plot: High Confidence .1 Stereonet: Magmatic Fabrics .3 Stereonet: All Data .4 Stereonet: High Confidence .3 Depth Bin Stereonets .2 Depth Bins: Magmatic Fabrics .1 MF Depth Bin: 30-100 Mbs (30 Measurements) .2 MF Depth Bin: 100-150 Mbs (37 Measurements) .3 MF Depth Bin: 150-200 Mbs (29 Measurements) .4 MF Depth Bin: 200-250 Mbs (29 Measurements) .5 MF Depth Bin 250-300 Mbs (11 Measurements) .6 MF Depth Bin: 300-350 Mbs (14 Measurements) .7 MF Depth Bin: 350-403 Mbs (33 Measurements) .3 Depth Bins: Layering .1 Layering Depth Bin: 30-100 Mbs (38 Measurements) .2 Layering Depth Bin: 100-150 Mbs (55 Measurements) .3 Layering Depth Bin: 150-200 Mbs (47 Measurements) .4 Layering Depth Bin: 200-250 Mbs (20 Measurements) .5 Layering Depth Bin: 250-300 Mbs (17 Measurements) .6 Layering Depth Bin: 300-350 Mbs (19 Measurements) .7 Layering Depth Bin: 350-403 Mbs (16 Measurements) .4 Depth Bins: All Data .1 All Data Depth Bin: 30-100 Mbs (68 Measurements) .2 All Data Depth Bin: 100-150 Mbs (92 Measurements) .3 All Data Depth Bin: 150-200 Mbs (76 Measurements) .4 All Data Depth Bin: 200-250 Mbs (49 Measurements) .5 All Data Depth Bin: 250-300 Mbs (28 Measurements) .6 All Data Depth Bin: 300-350 Mbs (33 Measurements) .7 All Data Depth Bin: 350-403 Mbs (49 Measurements). 81 CHAPTER IV – DISCUSSION.1 Magmatic Fabric vs.2 Orientation Variations with Depth .3 Formation of Magmatic Fabrics and Layering .4 Comparisons to Models of Crustal Accretion .5 Potential for an Alternative Model.
95 vi LIST OF TABLES Table 3.1 Summary of strikes found for each feature type within the respective depth bin. 40 vii LIST OF ILLUSTRATIONS Figure 1. Illustration of models for crustal accretion at fast spreading mid-ocean ridges.2 Geological and structural map from the Wadi Tayin massif of the Oman Ophiolite .1 Example comparison between a shipboard core image (unrolled whole core; left) and borehole image in Techlog (right).1 Reoriented Dip Azimuth vs. depth plot for all magmatic fabrics observed in this study.2 Histogram depicting frequency and cumulative percentages for all magmatic fabrics identified in this study.3 Reoriented Dip Azimuth vs.
Depth Plot for all layering structures observed in this study.4 Histogram displaying frequency and cumulative percentages of all instances of layering observed in Hole GT1.5 Reoriented Dip Azimuth vs. Depth plot for all structures observed in this study.6 Histogram displaying frequency and cumulative percentage for all data points observed in this study.7 Reoriented dip azimuth vs. depth plot for all measurements that have a confidence value of 4 or 5.8 Histogram displaying frequency and cumulative percentage for data points observed in this study that have a confidence value of 4 or 5.9 Stereonet of magmatic fabrics displayed as planes alongside a Rose Diagram in the center.10 Stereonet of magmatic fabric poles displayed alongside 1% area contouring with the contour interval spacing value set to 3%.11 Stereonet with respective poles of layering plotted.12 Stereonet displaying poles to layering with 1% area contouring with contour spacing intervals of 3%.13 Stereonet containing all data plotted as planes along with Rose diagram.14 Stereonet of all data displayed as poles and 1% area contouring with contour spacing intervals of 3%.15 Stereonet plot of all high confidence values plotted as planes and a Rose diagram.16 Stereonet plot of high confidence poles with 1% area contours in intervals of 3%.17 Comparison between depth bin stereonets for magmatic fabrics and layering from 30mbs to 150mbs.18 Comparison between depth bin stereonets for magmatic fabrics and layering from 150mbs to 300mbs.19 Comparison between depth bin stereonets for magmatic fabrics and layering from 300mbs to 403mbs.20 Stereonet plot of dip strike for all MF measurements in the 30-100 mbs depth bin.21 Stereonet plot for all MF measurements in the 30-100 mbs depth bin as poles with 1% area contours in intervals of 3%.22 Stereonet plot of dip and strike for all MF measurements in the 100-150 mbs depth bin.23 Stereonet plot for all MF measurements in the 100-150 mbs depth bin as poles with 1% area contours in intervals of 3%.24 Stereonet plot of dip and strike for all MF measurements in the 150-200 mbs depth bin.25 Stereonet plot of all MF measurements in the 150-200 mbs depth bin as poles with 1% area contours in intervals of 3%.26 Stereonet plot of dip and strike for all MF measurements in the 200-250 mbs depth bin.27 Stereonet plot for all MF measurements in the 200-250 mbs depth bin as poles with 1% area contours in intervals of 3%.28 Stereonet plot of dip and strike for all MF measurements in the 250-300 mbs depth bin.29 Stereonet plot for all MF measurements in the 250-300 mbs depth bin as poles with 1% area contours in intervals of 3%.30 Stereonet plot of dip and strike for all MF measurements in the 300-350 mbs depth bin.31 Stereonet plot for all MF measurements in the 300-350 mbs depth bin as poles with 1% area contours in intervals of 3%.32 Stereonet plot of dip and strike for all MF measurements in the 350-403 mbs depth bin.33 Stereonet plot for all MF measurements in the 350-403 mbs depth bin as poles with 1% area contours in intervals of 3%.34 Stereonet plot of dip and strike for all layering measurements in the 30-100 mbs depth bin.35 Stereonet plot for all layering measurements in the 30-100 mbs depth bin as poles with 1% area contours in intervals of 3%.36 Stereonet plot of dip and strike for all layering measurements in the 100-150 mbs depth bin.37 Stereonet plot for all layering measurements in the 100-150 mbs depth bin as poles with 1% area contours in intervals of 3%.38 Stereonet plot of all layering measurements in the 150-200 mbs depth bin as poles with 1% area contours in intervals of 3%.39 Stereonet plot of all layering measurements in the 150-200 mbs depth bin as poles with 1% area contours in intervals of 3%.40 Stereonet plot of dip and strike for all layering measurements in the 200-250 mbs depth bin.41 Stereonet plot for all layering measurements in the 200-250 mbs depth bin as poles with 1% area contours in intervals of 3%.42 Stereonet plot of dip and strike for all layering measurements in the 250-300 mbs depth bin.43 Stereonet plot for all layering measurements in the 250-300 mbs depth bin as poles with 1% area contours in intervals of 3%.44 Stereonet plot of dip and strike for all layering measurements in the 300-350 mbs depth bin.45 Stereonet plot for all layering measurements in the 300-350 mbs depth bin as poles with 1% area contours in intervals of 3%.46 Stereonet plot of dip and strike for all layering measurements in the 350-403 mbs depth bin.47 Stereonet plot for all layering measurements in the 350-403 mbs depth bin as poles with 1% area contours in intervals of 3%.48 Stereonet plot of dip and strike for the 30-100 mbs depth bin.49 Stereonet plot of the 30-100 mbs depth bin as poles with 1% area contours in intervals of 3%.50 Stereonet plot of dip and strike for the 100-150 mbs depth bin.51 Stereonet plot of the 100-150 mbs depth bin as poles with 1% area contours in intervals of 3%.52 Stereonet plot of dip and strike for the 150-200 mbs depth bin.53 Stereonet plot of the 150-200 mbs depth bin as poles with 1% area contours in intervals of 3%.54 Stereonet plot of dip and strike for the 200-250 mbs depth bin.55 Stereonet plot of the 200-250 mbs depth bin as poles with 1% area contours in intervals of 3%.56 Stereonet plot of dip and strike for the 250-300 mbs depth bin.57 Stereonet plot of the 250-300 mbs depth bin as poles with 1% area contours in intervals of 3%.58 Stereonet plot of dip and strike for the 300-350 mbs depth bin.59 Stereonet plot of the 300-350 mbs depth bin as poles with 1% area contours in intervals of 3%.60 Stereonet plot of dip and strike for the 350-403 mbs depth bin.61 Stereonet plot of the 350-403 mbs depth bin as poles with 1% area contours in intervals of 3%.1 Side by side comparison of stereonets and respective Rose diagrams for magmatic fabrics, layering, and all data. 88 xiii LIST OF ABBREVIATIONS CRF Coordinate Reference Frame Mbs Meters below surface SPO Shape-Preferred Orientation xiv CHAPTER I - INTRODUCTION 1.