Faculty of Science and Engineering School of Earth and Planetary Sciences Development and application of atom probe tomography to complex zircon grains Stephanie Dannett Montalvo Delgado 0000-0003-0601-2881 This thesis is presented for the Degree of Doctor of Philosophy of Curtin University March 2020 DECLARATION To the best of my knowledge and belief this thesis contains no material previously published by any other person except where due acknowledgment has been made. This thesis contains no material which has been accepted for the award of any other degree or diploma in any university. Signature: Date: 18/03/2020 iii DEDICATION To my partner Danny Fleming. You are an amazing person, always there to support me, even through tough times. Without you this thesis would not have been completed. For that and much more, I thank you. v ABSTRACT Atom probe tomography (APT) is a 3D analytical technique that provides the elemental composition of materials at sub-nanometre resolutions. Although originally developed for material science applications, recent advances in APT technology has expanded the applicability to other disciplines, including geological samples. The high spatial resolution of APT opens new avenues of geochemical studies. The few APT studies conducted on zircon have focussed on the nanogeochemistry and nanogeochronology of standards, igneous and metamorphic grains. However, the current applications of APT with zircon grains are limited with no systematic studies conducted on complex grains. This project is aimed at further developing APT techniques to zircon through the novel application of APT to meteoritic, altered and shocked zircon grains. Microscale zircon grains from the Bunburra Rockhole meteorite were analysed using APT to better understand the origin and formation history of the meteorite. The APT geochemical results suggested a similar source melt for the different clast that made up the meteorite. This data was later used to discern between the parent body of Bunburra Rockhole and the asteroid 4 Vesta. An altered zircon from the Lalla Rookh Sandstone formation was analysed with APT to understand the composition of the hydrothermal alteration zones. The nanogeochemistry of the grain showed a high concentration of trace elements in metamict areas, Pb clusters in crystalline areas, and it revealed a connection between the U, radiation damage and APT specimen yield. The APT data was also used to confirm the age of the metamorphic event that affected the grain. The use of APT in shocked zircons from the Stac Fada impact structure (Scotland) provided evidence of trace element mobility associated with the zircon-to- reidite transformation. These results were used to develop a new model for the phase transformation that includes the martensitic transformation and short-range diffusion components that occurs during an impact event. This PhD project has developed new applications for APT in the analysis of complex zircon grains and provides a basis and lessons learnt for further nanoscale geochemical and geochronological studies. The project results offer an improved understanding of how APT may be applied to certain complex grains and provides a framework for new geological applications and to other minerals. vii ACKNOWLEDGEMENTS The decision of pursuing a PhD in Earth and Planetary Sciences at Curtin University was an easy one for me. However, the path was not as easy. Along the way, I encountered unexpected ups and downs involving my PhD research and my personal life. Yet, that is how science (and life) works. Nonetheless, I stand by my decisions and, even though there were some frustrating moments, I am pleased and proud of what I have learned and accomplished throughout my PhD years. The completion of this thesis could not have been possible without the help of the people I have met along this journey. First, I would like to thank my partner for all his support, understanding and editing help. This thesis would have been very different without his help. Secondly, I would also like to thank my mother, younger sister and stepfather for supporting my decision to move to the furthest place from them I can possibly think of. I know it was not easy for them, but they still supported me. My supervisors Steven M. Reddy, David W. Saxey, William D. Rickard and Denis Fougerouse have provided me their guidance (scientific writing, technical instruments, general knowledge) during my PhD, which has contributed to my growth as a scientist. They gave me the opportunity to work, learn and gain experience with state-of-the-art instruments at Curtin University. The knowledge I have acquired thanks to them is invaluable and much appreciated. I would also like to thank my co-authors and collaborators for their input and assistance in the individual case studies. They are Zakaria Quadir (Curtin Univ.), Tim E. Johnson (Curtin Univ.), Gretchen K. Benedix (Curtin Univ.), Chris Kirkland (Curtin Univ.), Thorsten Geisler (Univ. of Bonn, Germany) and Alexander G. Webb (China Univ. of Geosciences). Of course, this project relied upon the assistance and guidance of the technical staff of the John de Laeter Centre, which includes Ms Elaine Miller, Ms Kelly Merigot, Ms Veronica Avery and Mr Hao Gao. Other professors, technical staff and PhD students provided me with additional guidance, encouragement and friendship during my PhD at Curtin University. These are Aaron Cavosie, Andrew Putnis, Nick Timms, Pete Kinny, Adam Frew, Rick Verberne, Jennifer Porter, Sonia Armandola, Cilva Joseph, Johanna Heeb, Tommaso Tacchetto, Tobias Wengorsch, Morgan Cox, Alexander Walker, Tania Hidalgo, Ellie Sansom and Timmons Erickson. ix LIST OF PUBLICATIONS • Nanoscale constrains on the shock-induced transformation of zircon to reidite Montalvo, S. D., Reddy, S. M., Saxey, D. W., Rickard, W. D. A., Fougerouse, D., Quadir, Z., and Johnson, T. E., 2019, Nanoscale constraints on the shock-induced transformation of zircon to reidite: Chemical Geology, v. 507, p. 85-95. I warrant that I have obtained, where necessary, permission from the copyright owners to use any third-party copyright material reproduced in the thesis (e.g. artwork), or to use any of my own published works (e.g. journal articles) in which the copyright is held by another party (e.g. publishers, co-author). xi TABLE OF CONTENTS Declaration iii Dedication v Abstract vii Acknowledgements ix List of Publications xi Table of Contents xiii List of Figures xvii List of Supplementary Figures xix List of Tables xxi List of Supplementary Tables xxi Chapter 1 Introduction and Overview 1 Background 1 Rationale 7 Thesis structure 7 Figures 9 References 13 Chapter 2 Trace element analysis of micrometre-scale zircons in Bunburra Rockhole meteorite from atom probe tomography 17 Abstract 18 Introduction 19 Methods 21 Results 24 Petrographic analysis 24 Geochemical Results 26 Discussion 28 Zircon characteristics 28 Evolution of Bunburra Rockhole 29 Comparison of Bunburra Rockhole and eucrites 30 Conclusion 31 Acknowledgements 32 Figures 33 Supplementary Material 41 References 50 xiii Chapter 3 Complex history of a detrital zircon obtained by textural and trace element analyses 53 Abstract 54 Introduction 55 Geologic settings 57 Analytical methodology 58 Results 65 Textural variations 65 Nanoscale analyses 67 U-Pb geochronology 70 Discussion 70 Textural characterization 70 Evolutional history of the zircon grain 72 APT analytical aspects 73 Nano-features and trace element distribution 74 Conclusion 76 Acknowledgements 77 Figures 78 Supplementary Material 88 References 93 Chapter 4 Nanoscale constraints on the shock-induced transformation of zircon to reidite 99 Chapter 5 Strategies for nanoscale analysis of shocked zircon grains 111 Introduction 112 Shock metamorphism 113 Geological setting 113 Methodology 113 Results 122 Discussion 130 Indian Ocean zircon - control sample 130 Distribution of trace elements in Stac Fada 131 Geochronological analysis 133 Advantages and limitations of analytical techniques 133 Conclusion 136 Figures 138 xiv Supplementary Material 153 References 164 Chapter 6 Conclusion and future recommendations 167 Distribution of trace elements in complex zircon grains 167 Micrometre size grains 167 Complex textures within a grain 167 Structures in shocked zircon grains: Insights into phase transformation 168 Geochronological application of APT in zircon 169 APT specimen yield 169 Future Recommendations 173 Figures 174 References 176 Appendix A Statements from co-authors for Ch. 4 179 Appendix B Higher resolution Figure 6.1 181 Appendix C Attribution statements 185 References 191 xv LIST OF FIGURES Figure 1.1 Schematic diagram of a local electrode atom probe. ............................. 9 Figure 1.2 Potential energy curve diagram of an ion at the surface of the APT ... 10 Figure 1.3 Analytical lateral resolution and the detection limit. ........................... 11 Figure 1.4 Outline of some of the imaging. ........................................................... 12 Figure 2.1 A BSE image of the Bunburra Rockhole sample. ................................ 33 Figure 2.2 EBSD phase maps from the FG domain. ............................................. 34 Figure 2.3 Histogram of the size distribution of the zircon grains. ....................... 35 Figure 2.4 EBSD maps of the five zircon grains analysed .................................... 36 Figure 2.5 APT data for specimen M3 (~91 million ions).. .................................. 37 Figure 2.6 A visual representation of the trace element