STABLE STRONTIUM ISOTOPE FRACTIONATION IN ABIOTIC AND MICROBIALLY MEDIATED BARITE IN MODERN CONTINENTAL SETTINGS A dissertation submitted to Kent State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy by Inoka Hasanthi Widanagamage December 2015 Dissertation written by Inoka Hasanthi Widanagamage B.S., University of Peradeniya, 2008 M.S., Kent State University, 2011 Ph.D., Kent State University, 2015 Approved by Dr. Elizabeth M. Griffith Co-Chair, Doctoral Dissertation Committee Dr. David M. Singer Co-Chair, Doctoral Dissertation Committee Dr. Joseph D. Ortiz Members, Doctoral Dissertation Committee Dr. Alison J. Smith Dr. John M. Senko Dr. Darren L. Bade Accepted by Dr. Daniel K. Holm Chair, Department of Geology Dr. James L. Blank Dean, College of Arts and Sciences TABLE OF CONTENTS TABLE OF CONTENTS ............................................................................................ iii LIST OF FIGURES .................................................................................................. viii LIST OF TABLES ...................................................................................................... xi PREFACE .................................................................................................................. xii ACKNOWLEDGEMENTS ...................................................................................... xiii DEDICATION .......................................................................................................... xiv ABSTRACT ............................................................................................................... 16 CHAPTER 1 .............................................................................................................. 19 INTRODUCTION .................................................................................................. 19 Research Motivation ........................................................................................... 19 Background ......................................................................................................... 21 Barite crystal structure and Sr incorporation .................................................. 21 Presence of barite and mechanisms of formation ........................................... 22 Barite at continental settings ........................................................................... 23 Study Sites .......................................................................................................... 24 Strontium (Sr) isotopes and mass dependent fractionation ................................ 25 Microbially-induced isotopic fractionation in other alkali earth metals ............. 26 Research objectives and goals ............................................................................ 27 Research Hypotheses .......................................................................................... 28 Dissertation Outline ............................................................................................ 31 iii CHAPTER 2 .............................................................................................................. 34 STABLE STRONTIUM ISOTOPE FRACTIONATION IN SYNTHETIC BARITE ................................................................................................................................ 34 Widanagamage I.H., Schauble E.A., Scher, H.D. and Griffith E.M. (2014)............ 34 Abstract ............................................................................................................... 34 Introduction ........................................................................................................ 35 Notations and Methods ....................................................................................... 39 Notation........................................................................................................... 39 Modeling methods .......................................................................................... 39 Analytical methods ......................................................................................... 45 Laboratory precipitation experiments ......................................................... 45 Saturation calculations ................................................................................ 49 Barite crystal morphology .................................................................................. 50 Bulk elemental concentrations ............................................................................ 50 Sample preparation for isotopic analysis ............................................................ 51 Isotopic analysis ................................................................................................. 54 Results ................................................................................................................ 56 Theoretical equilibrium fractionation factors ................................................. 56 Model structures and vibrational (phonon) frequencies .............................. 56 Estimated equilibrium 88Sr/86Sr fractionation factors ................................. 59 Accuracy of theoretical estimates ............................................................... 63 Synthetic barite ............................................................................................... 65 Crystal morphology ..................................................................................... 65 Sr/Ba ratio in barite ..................................................................................... 67 iv Sr-isotope fractionation ............................................................................... 71 Discussion ........................................................................................................... 74 Factors controlling barite crystal morphology ................................................ 74 Factors controlling Sr elemental and isotopic composition in barite .............. 76 Conclusions ........................................................................................................ 82 CHAPTER 3 .............................................................................................................. 84 CONTROLS ON STABLE SR- ISOTOPE FRACTIONATION IN CONTINENTAL BARITE ................................................................................................................. 84 Abstract ............................................................................................................... 84 Introduction ........................................................................................................ 85 Study sites ........................................................................................................... 88 Methods .............................................................................................................. 91 Water chemistry .............................................................................................. 91 In situ ........................................................................................................... 91 Anions ......................................................................................................... 91 Cations ......................................................................................................... 92 Saturation calculations ................................................................................ 92 Barite elemental ratios ................................................................................. 92 Isotopic analysis .............................................................................................. 93 Sample preparation ...................................................................................... 93 Mass spectrometry....................................................................................... 94 Scanning electron microscopy ........................................................................ 95 Synchrotron x-ray microprobe analysis .......................................................... 96 Results ................................................................................................................ 97 v Natural water and barite geochemistry ........................................................... 97 Strontium speciation and distribution in natural barite ................................. 108 µ-XRF ....................................................................................................... 108 µ-XRD ....................................................................................................... 110 Discussion ......................................................................................................... 111 Precipitation of barite in a continental setting .............................................. 111 Bulk Sr content of barite ........................................................................... 115 Micro-scale Sr heterogeneity ........................................................................ 116 Source of Sr in barite .................................................................................... 117 Processes controlling stable Sr-isotope fractionation in continental barite .. 118 Mineralogy control .................................................................................... 119 Physicochemical controls .........................................................................