DEVELOPING THE 60Fe-60Ni SYSTEM FOR EARLY SOLAR SYSTEM CHRONOLOGY A DISSERTATION SUBMITTED TO THE GRADUATE DIVISION OF THE UNIVERSITY OF HAWAI‘I AT MĀNOA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY IN GEOLOGY AND GEOPHYSICS AUGUST 2015 By: Myriam Telus Dissertation Committee: Gary R. Huss, Chairperson Kazuhide Nagashima Alexander N. Krot G. Jeffrey Taylor Jonathan P. Williams Keywords: iron, nickel, aluminum, magnesium, radionuclides, meteorites To my husband Nathanael, my endless source of inspiration and joy i ACKNOWLEDGEMENTS I am amazed by how enjoyable graduate school and working toward my Ph.D. has been. For this, I am especially thankful to my advisor Gary Huss. His patience and dedication to helping me grow as a scientist has made this such a rewarding experience. Thanks to all the members of our cosmochemistry group at UH. They are simply the best folks to work with. Thanks to Kazu Nagashima for patiently teaching me to use the ion probe, for working with me on all of my projects and for serving on my dissertation committee. Thanks to Ryan Ogliore for helping me understand proper SIMS data analysis and for traveling all the way to Australia to help with my synchrotron measurements. Thanks to Sasha Krot and Jeff Taylor for serving on my dissertation committee, eagerly discussing ideas with me and for helping me with various aspects of my research. Special thanks to Jonathan Williams, an honorary member of the cosmochemistry group, for hiking all the way from IFA for my dissertation committee meetings. Thanks to Ed Scott for helping with my work on H4 chondrites. Thanks to grad students, Christie Jilly and Caroline Caplan, former postdocs, Manavi Jadhav, Lydie Bonal, Kentaro Makide, Chung-kun Park and Trish Doyle and the assistant lab manager, Aurelien Thomen. They are all part of what makes the cosmochemistry group so special. Thanks to Eric Hellebrand, another honorary member of the group. He has helped all of us with our electron probe analyses. Thanks also to all of my other collaborators including Shogo Tachibana who helped with my Fe-Ni SIMS analyses; Daryl Howard, James Cleverley, and Andy Tomkins who helped with my proposal and analyses at the Australian Synchrotron; and Matt Newville who helped with my analyses at the Advanced Photon Source. I want to acknowledge that funding for my research and education are from ii Gary’s NASA grant (NNX11AG78G) and my NASA Earth & Space Science Fellowship (NNX11AN62H). Thanks to the Watamull Scholarship and the Gates Millennium Scholarship for their financial support. Thanks also to the Smithsonian and the Meteorite Working Group for supplying the samples for this research. Many thanks to all the faculty and staff in GG and HIGP, especially Julia Hammer, Jeff Gillis-Davis, John Mahoney, and Przemyslaw Dera who have all helped in some form with my research or served on one of my committees. Thanks to all of the wonderful graduate students who gave me advice and helped me out along the way, especially Elise Rumpf, my wonderful officemate. Thanks also to my previous advisors from UChicago, Nicolas Dauphas, Andy Davis, and Mike Savina for encouraging me to pursue my Ph.D. Finally, I am especially thankful for my husband Nathanael, my parents, my siblings, Josh, Jessica, Nadeige, Rose, and James, my uncle Yonel, and all of the friends I have made here in Hawaii, especially Ann, Wilfred, Polly, Grace, and Norbert. There are so many people to thank and I am sure that I have missed someone, but you all should know that without your support and your sacrifice this would not have been possible. iii ABSTRACT This dissertation focuses on in situ Fe and Ni isotope analyses of chondrules from unequilibrated ordinary chondrites (UOCs) using the ion microprobe in order to constrain the initial 60Fe/56Fe ratio of UOC chondrules for early solar system chronology. Most of the chondrules analyzed for this dissertation do not have resolved excesses in 60Ni. A few chondrules have clear excesses in 60Ni (up to ~30‰) that can only be explained by the decay of 60Fe. However, the isochrons are clearly disturbed as shown by the weak correlation between the excesses in 60Ni and the Fe/Ni ratios. This, along with the discrepancies between the initial ratios inferred from bulk and in situ analyses, indicates that the Fe-Ni isotopic system in UOCs was disturbed. Synchrotron X- ray fluorescence maps of Fe and Ni and other trace elements in UOC chondrules confirm this. We found Fe and Ni enrichment along chondrule fractures, indicating extensive open system Fe-Ni redistribution occurred between chondrules and the surrounding matrix. These complications make the Fe-Ni isotope data difficult to interpret. Nevertheless, our data indicate that the initial 60Fe/56Fe ratio of UOC chondrules is between 5×10-8 and 2.6×10-7. Our ion microprobe measurements consist of counting Fe and Ni ions from a chondrule and calculating isotope ratios from those counts. However, ratios calculated this way are systematically higher than the true ratio in the sample. The bias increases proportionally with decreasing count rates of the normalizing isotope and can produce linear correlations similar to those of an isochron. This dissertation provides a detailed discussion of the influence of ratio bias on isochrons and it includes re-calculated ratios for several in situ studies, including most of the previously published in situ Fe-Ni data. iv 26 26 Additionally, a study of the influence of ratio bias on in situ Al- Mg (t1/2=0.7 Myr) systematics of plagioclase from H4 chondrites is included in this dissertation. We find that ratio bias is not significant for these analyses. We argue that the 26Al-26Mg ages for these chondrites date impact excavation and cooling at the surface of the H chondrite parent body, not cooling at depth as the onion shell model predicts. v TABLE OF CONTENTS ACKNOWLEDGEMENTS ............................................................................................. ii ABSTRACT ...................................................................................................................... iv LIST OF TABLES ........................................................................................................... xi LIST OF FIGURES ....................................................................................................... xiii CHAPTER 1. INTRODUCTION .................................................................................... 1 1.1 Background ............................................................................................................... 2 1.2 Importance of the 60Fe-60Ni short-lived radionuclide ............................................... 5 1.3 Dissertation outline ................................................................................................... 9 CHAPTER 2. IN SITU 60Fe-60Ni SYSTEMATICS OF CHONDRULES FROM UNEQUILIBRATED ORDINARY CHONDRITES ................................................... 11 2.1 ABSTRACT ............................................................................................................ 12 2.2 INTRODUCTION .................................................................................................. 13 2.3 METHODS ............................................................................................................. 17 2.3.1 Sample selection .............................................................................................. 17 2.3.2 Secondary ion mass spectrometry .................................................................... 18 2.3.3 Data analysis .................................................................................................... 24 2.4 RESULTS ............................................................................................................... 26 2.4.1 Initial ratios with large uncertainties due to low Fe/Ni ratios .......................... 27 2.4.2 Initial ratios with large uncertainties due to limited spread in Fe/Ni ratios ..... 27 vi 2.4.3 Unresolved initial ratios, despite high Fe/Ni ratios ......................................... 29 2.4.4 Resolved initial ratios, but large MSWD values .............................................. 30 2.4.5 Constraining the initial 60Fe/56Fe ratio of UOC chondrules ............................. 33 2.4.6 Identifying our best chondrule datasets and constraining upper limits ............ 38 2.4.7 Constraining the upper limit on the initial 60Fe/56Fe ratio of UOCs ................ 39 2.5 DISCUSSION ......................................................................................................... 41 2.5.1 Complications from Fe-Ni mobilization in UOC chondrules .......................... 42 2.5.2 Interpretation of unresolved initial ratios require caution ................................ 44 2.5.3 Constraints from chondrules with high initial ratios and large MSWD values 45 2.5.4 Comparison with ICPMS and TIMS UOC chondrule data ............................. 49 2.5.5 Coordinated bulk & in situ analyses of UOC chondrules ................................ 50 2.5.6 Constraining the source of 60Fe in the early solar system ................................ 51 2.5.7 Developing the 60Fe-60Ni system for early solar system chronology .............. 54 2.6 CONCLUSIONS .................................................................................................... 56 CHAPTER 3. MOBILITY OF IRON AND NICKEL AT LOW TEMPERATURES AND IMPLICATIONS FOR 60Fe-60Ni SYSTEMATICS OF CHONDRULES FROM