Heat capacity of high pressure minerals and phase equilibria of Cretan blueschists by Matthew Rahn Manon A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy (Geology) in The University of Michigan 2008 Doctoral Committee: Professor Eric J. Essene, Chair Professor Rebecca Ann Lange Professor Youxue Zhang Associate Professor Steven M. Yalisove Matthew Rahn Manon 2008 Acknowledgments Cheers to all the grad students who have gone and come through CC-Little over the years. Zeb, Steven, Jim, Chris, Katy, Phillip, Franek, Eric, Tom, Darius, Sarah, Sara, Abir, Laura, Casey, Sam, John and anyone else I’ve been to learned something from, or argued something with. From early nights at Dominicks for subductology “seminars” through to the FWC, Michigan has been a fun place to live. Thanks to Anne Hudon, whos made sure I haven’t been able to place myself in inextricable holes. Thanks also to those from earlier in my life. College professors like Ken Hess or Barbara Nimmersheim who, in their very different ways inspired me to explore what it is I know. I’ll always remember time spent with Bob Wiebe who introduced me to the wild unknown of geology. Immeasurable thanks go to Eric Essene. The fieldtrips we took the first few years were good adventures. He’s always put aside his own issues to be there for me to talk to, especially when I didn’t deserve it. Eric’s scientific curiosity, and mental rigor are deservedly well known. His patience with me may be one of his great, unsung virtues. Of course, to my parents I owe debts and thanks which can never be paid. This whole experience, especially the last few months, sheds new light on my high-school years, and the struggle they endured. They’ve always inspired me to examine and enjoy the world. I do believe I wouldn’t have gotten this far without the love and support of Holli, the woman who is now my wife. She definitely understands how this feels. You came into my life at the very start of this process, and have been by my side through it all. ii Table of Contents Acknowledgements ......................................................................................................... ii List of Figures ................................................................................................................ iv List of Tables.................................................................................................................. vi List of Appendices..........................................................................................................vii Chapter I Introduction...................................................................................................... 1 Chapter II Low-temperature heat capacity measurements and new entropy data for sphene (titanite): implications for thermobarometry of high pressure rocks................. 8 Introduction................................................................................................................. 8 Methods ................................................................................................................... 10 Results ..................................................................................................................... 11 Heat capacity data.................................................................................................... 14 Volume data ............................................................................................................. 18 Enthalpy of formation................................................................................................ 20 Thermobarometry ..................................................................................................... 25 Conclusions.............................................................................................................. 30 Chapter III Low-temperature heat capacity of TiO2-II and the rutile/TiO2-II phase boundary .................................................................................................................. 36 Introduction............................................................................................................... 36 Previous Work .......................................................................................................... 37 Experimental Methods.............................................................................................. 39 Results .................................................................................................................... 40 STP Estimation......................................................................................................... 49 Conclusions.............................................................................................................. 56 Chapter IV Mineral assemblages, phase equilibria and the conditions of metamorphism in Cretan metabasites............................................................................................... 59 Introduction............................................................................................................... 59 Geologic Setting ....................................................................................................... 61 Previous Work .......................................................................................................... 63 Sample Descriptions................................................................................................. 68 Electron Microprobe Analysis Procedures ................................................................ 75 Mineral Normalizations ............................................................................................. 78 Thermodynamic Data and Metamorphic Reactions .................................................. 89 Conclusions............................................................................................................ 102 Chapter V Conclusions ............................................................................................... 108 Appendices ................................................................................................................. 114 iii List of Figures Figures 2.1 Low-temperature Cp data of sphene ....................................................................... 11 2.2 Cp of sphene from various authors.......................................................................... 14 2.3 Residuals for published Cp equations ..................................................................... 16 2.4 Volume data and equations for sphene ................................................................... 19 2.5 Experimental reversals of TARK by Manning and Bohlen (1991) ............................ 22 2.6 Constraints on the reaction rutile+quarz+calcite=sphene+CO2 ............................... 23 2.7 Log10K diagrams of sphene-bearing barometers used in the literature.................... 26 3.1 Low-temperature Cp data for TiO2-II ....................................................................... 41 3.2 DSC heat capacity measured for TiO2-II ................................................................ 43 3.3 Fits and residuals calculated from fitting the Cp data for TiO2-II to the Debye/Einstein equation (Eqs 3.2-3.4) .............................................................................................. 45 3.4 Polynomial regressions along with residuals for TiO2-II fit to Eq 3.5 at low temperatures ............................................................................................................ 46 3.5 Polynomial regressions along with residuals for TiO2-II fit to Eq 3.5, at high temperatures ............................................................................................................ 47 3.6 The mean S˚298 and sample standard deviation calculated for different sized populations of dataset created by normally varying data points according to their uncertainty................................................................................................................ 49 3.7 A comparison of the locus of several polymorphic reactions (solid lines), with their Clausius-Clapeyron slopes calculated at STP (dotted lines) ..................................... 50 3.8 Experimentally determined slopes and reversals on the rutile/TiO2-II phase boundary from Akaogi et al. (1992) and Withers et al. (2003)................................................... 54 3.9 The Cp of TiO2-II (diamonds) compared with that of rutile (squares) ....................... 55 3.10 ∆S(r) calculated for Eq (3.1), based on the data shown in Fig. 3.9 illustrating the imminent crossover predicted by the data ................................................................ 55 4.1 Generalized geologic map of Greece ...................................................................... 60 4.2 Simplified geologic map of Crete, Greece ............................................................... 62 4.3 Estimates of the metamorphism in the PQ unit on Crete made by other workers .... 66 4.4 Typical pumpellyite-bearing assemblage form the Cretan metabasalts with chlorite (Chl) and muscovite (Mu) from sample cr04-62 ....................................................... 69 4.5 Closeup of a tabular domain, inferred to be former igneous plagioclase, from sample cr04-28b ................................................................................................................... 70 4.6 A large glaucophane (Gl) crystal