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Petrographical, Thermochronological, and Geochemical Analysis of Pan-African Age Metamorphic and Shear Zone Rocks in Western Ethiopia and Southern Sri Lanka

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Petrographical, Thermochronological, and Geochemical Analysis of Pan-African Age Metamorphic and Shear Zone Rocks in Western Ethiopia and Southern Sri Lanka PETROGRAPHICAL, THERMOCHRONOLOGICAL, AND GEOCHEMICAL ANALYSIS OF PAN-AFRICAN AGE METAMORPHIC AND SHEAR ZONE ROCKS IN WESTERN ETHIOPIA AND SOUTHERN SRI LANKA A thesis submitted to the Kent State University Graduate College in partial fulfillment of the requirements for the degree of Master of Science by Chelsea A. Lyle May, 2014 Thesis written by Chelsea A. Lyle B.A. SUNY Geneseo, 2010 M.S. Kent State University, 2014 Approved by Daniel Holm, Advisor Daniel Holm, Chair, Department of Geology Janis Crowther, Dean, College of Arts and Sciences ii TABLE OF CONTENTS LIST OF FIGURES ..................................................................................................v LIST OF TABLES ....................................................................................................vi ACKNOWLEDGEMENTS ......................................................................................vii Summary ....................................................................................................................1 Chapter I. Introduction .......................................................................................3 Pan-African Orogeny ............................................................6 Arabian-Nubian Shield .........................................................7 Geology of Western Ethiopia ................................................10 Geology of Central and South-Eastern Sri Lanka..................16 Study Area ............................................................................18 II. Petrographic Characteristics .............................................................22 Sample MR8-Ethiopia ...........................................................24 Sample MR1-Ethiopia ...........................................................26 Sample MR2-Ethiopia ...........................................................28 Sample MR3-Ethiopia ...........................................................30 Sample MR4-Ethiopia ...........................................................32 Sample MR6-Ethiopia ...........................................................34 Sample SLR2-Sri Lanka ........................................................36 Sample SLR3-Sri Lanka ........................................................38 Sample SLR6-Sri Lanka ........................................................40 Sample SLR7-Sri Lanka ........................................................42 Summary ................................................................................44 III. 40Ar/39Ar Thermochronology .............................................................45 Methodology ..........................................................................45 Results ....................................................................................47 Summary ................................................................................55 iii IV. Lithogeochemsitry and Magnetic Mineralogy ...................................56 Methodology ..........................................................................57 Lithogeochemistry .................................................................57 Magnetic Mineralogy .............................................................58 Results ....................................................................................60 REE Geochemistry.....................................................60 Harker Diagrams ........................................................63 Isocon Plots ................................................................65 Curie Point Temperatures ..........................................68 Low-Temperature Magnetic Transitions ...................71 Summary ....................................................................74 V. Conclusion .........................................................................................75 Ethiopia ..................................................................................75 Sri Lanka ................................................................................78 REFERENCES .........................................................................................................79 iv LIST OF FIGURES Figure 1. Map of East and West Gondwana during the Pan-African Orogeny .............4 2a. Map of Ethiopia .............................................................................................5 2b. Map of Sri Lanka ...........................................................................................6 3. Simplified tectonic evolution of the Arabian Nubian Shield ..........................9 4. Map showing location areas for previous studies and the Mengi River megashear zone .............................................................................................12 5. Geologic Map of Mengi River megashear zone .............................................20 6. Outcrop of Mengi River megashear zone L-S tectonics showing a strong stretching lineation ........................................................................................23 7. MR8- photomicrograph and hand sample.......................................................25 8. MR1- photomicrograph and hand sample.......................................................27 9. MR2- photomicrograph and hand sample.......................................................29 10. MR3- photomicrograph and hand sample......................................................31 11. MR4- photomicrograph and hand sample......................................................33 12. MR6- photomicrograph and hand sample......................................................35 13. SLR2- photomicrograph and outcrop ............................................................37 14. SLR3- photomicrograph and outcrop ............................................................39 15. SLR6- photomicrograph ................................................................................41 16. SLR7- photomicrograph ................................................................................43 17. Ethiopian sample (MR3) age and K/Ca spectra .............................................48 18. Sri Lankan sample (SLR2, SLR3, SLR6, SLR7) age and K/Ca spectra .......49 19. REE concentration plot for MR1, MR2, MR4, and MR8 .............................63 20. Harker diagrams for MR1, MR2, and MR4 ...................................................64-65 21. Isocon plots ....................................................................................................68 22. Curie point temperature plots........................................................................69-70 23. Low-temperature magnetic transitions ..........................................................72-73 v LIST OF TABLES Tables 1. Summary of stages of tectonism during the Pan-African Orogeny ........16 2. Age results and isotopic data from Ar/Ar dating analysis .......................50-52 3. Summary of plateau and total gas ages from 40Ar/39Ar data .................52 4. Known low-temperature magnetic transitions .........................................59 5. Known Curie and Néel temperatures .......................................................59 6. Oxide weight percent values for sample MR1, MR2, MR4, and MR8 ...60 7. Rare earth and Trace element concentrations in ppm for sample MR1, MR2, MR4, and MR8 ..............................................................................61-62 8. Scale vectors and scaled values used to produce isocon plots .................67 vi ACKNOWLEDGEMENTS I wish to express my sincerest appreciation to all those who helped me throughout my thesis project. Firstly, I would like to thank my advisor Daniel Holm for his guidance, patience, and encouragement throughout all of my studies and research at Kent State University. I would also like to thank my committee members Donald Palmer and David Hacker for their assistance in my research. I owe many thanks to Yonathan Admassu for his knowledge, enthusiasm, and resources on Ethiopian geology. Also, a special thanks to Hasanthi Widanagamage for allowing me to use her samples and for her help with the geology of Sri Lanka. I would like to thank my friends and colleagues at both Kent State University and SUNY Geneseo, many of whom supported me and listened to me as I worked through my research. Not only have I made great friendships while at school, I have met incredibly intelligent people who are always willing to help in any way possible. It is this support that keeps me driven to keep going every day. I must thank the many professors at SUNY Geneseo for making me learn to love research and inspiring me to continue on to graduate school. Their continued support has helped me to succeed more than they know. Lastly, I need to thank my family for their love and support. Especially to my parents, who continue have faith in me and remind me I can do anything. vii SUMMARY Petrographical, thermochronological, and geochemical analyses were performed on shear zone related Pan-African samples in west Ethiopia and southeast Sri Lanka. Five sheared samples of either metagranites or amphibolites and two samples of undeformed granitic rock were collected from the Mengi River megashear zone (MMSZ) in western Ethiopia. Four gneisses were collected from within and around the Highland Complex- Vijayan Complex boundary zone in central to eastern Sri Lanka. The MMSZ samples contain abundant fine-grained recrystallized quartz and feldspar grains with secondary late seams of euhedral to anhedral magnetic
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