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Reconstructing Past Antarctic Ice Flow Paths in the Ross

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Reconstructing Past Antarctic Ice Flow Paths in the Ross RECONSTRUCTING PAST ANTARCTIC ICE FLOW PATHS IN THE ROSS EMBAYMENT, ANTARCTICA USING SAND PETROGRAPHY, PARTICLE SIZE AND DETRITAL ZIRCON PROVENANCE Andrea J. Schilling Submitted to the faculty of the University Graduate School in partial fulfillment of the requirements for the degree Master of Science in the Department of Earth Sciences, Indiana University March 2010 Accepted by the Faculty of Indiana University, in partial fulfillment of the requirements for the degree of Master of Science. ______________________________________ Kathy Licht, PhD ______________________________________ R. Jeffrey Swope, PhD Master’s Thesis Committee ______________________________________ Joseph Pachut, Jr., PhD ii ACKNOWLEDGEMENTS This product could have not been accomplished without the help of many people. I first must thank my advisor, Dr. Kathy Licht, without whom this project would not have been possible. Dr. Licht brought me into the Antarctic world and allowed me so many great opportunities; for that I am very grateful. Kathy is truly a remarkable person and I feel very blessed to have her as a mentor and friend. Thank you, Kathy, for having so much confidence in me. I also am very appreciative to Dr. Jeffrey Swope for his time, support and critiques. Dr. Swope’s passion and enthusiasm for science is contagious. Thank you for allowing me my first bit of research (all those black rocks!). I also want to thank all of the faculty and staff, Dr. Pachut in particular, and the Earth Science department for their input and support. A huge thanks to all my friends, fellow graduate and undergraduate students at IUPUI for sharing these past few years. To Matthew Hennessy, for being a great lab partner and always being there to make me laugh! Thank you, Matt, for all of your support, understanding and of course, your voice of reason. Last, but definitely not least, I want to thank my family. My parents, Steve and Carla Schilling, have always been there for me with unlimited support and encouragement. Without their love and constant support I would not be where I am today. Thank you, Mom and Dad, for believing in me. To my brother, Chris, who motivates me by his dedication. We are happy to have you home. To my sister, Maggie, who inspires me by her ambition and resilience. Thank you for always being there. iii This research was funded by the IUPUI Research Support Funds Grant. iv ABSTRACT Andrea J. Schilling Reconstructing past Antarctic ice flow paths in the Ross Embayment, Antarctica using sand petrography, particle size and detrital zircon provenance Tills for this study were analyzed from sites in East Antarctica (EA), West Antarctica (WA) and along a transect in the Ross Sea. Particle size, sand petrography, and detrital zircons were used to provide new information on the subglacial geology of Antarctica, as well as assisting in the reconstruction of Last Glacial Maximum (LGM) ice flow paths. Statistical analyses using the Kolmogorov-Smirnov (K-S test) reveal that EA and WA zircon age distributions are distinct at a P-value <0.05. This makes it possible to trace the unique signatures from EA and WA into the Ross Sea. The majority of Bindschadler and Whillans Ice Stream samples are dominated by polymict grains and silt and clay, while Kamb is dominated by sand and only three of the four cores are polymict rich. WA ice streams (Kamb, Bindschadler, and Whillans, all contain Ross age (550-500 Ma) and Grenville age (1100-1000 Ma) populations. Kamb and Bindschadler contain a young zircons age population (~100 Ma), whereas Whillians Ice Streams is missing the ~100 Ma age populations but contains a ~230 Ma age population. The presence of the low sand, the felsic-intermediate igneous lithic fragments and unique U-Pb ages observed in till samples taken from Mount Howe and Davis Nunatak indicate that subglacial material is being transported from East Antarctic sites and deposited at Mount Howe and Davis Nunatak. All EA samples collected at the head and middle of major EA outlet glaciers contain grains whose age of formation is consistent with the Ross Orogeny and all samples showed small age populations scattered v throughout the Proterozoic. The most noteworthy peaks occur from the Permian through the Triassic. EA outlet glacier samples, Beardmore Glacier (BG), Davis Nunatak (DN), Bates Nunatak (BN), and Cloudmaker (CM) (all where Beacon Group rocks have been mapped) match age populations from previous published Beacon samples of ~240-270 Ma. This may suggest that the signature from the Beacon Supergroup may be identifiable. These outlet samples are a representation of material being transported into the TAM. The fingerprint of each outlet glacier will be altered as it crosses the TAM, resulting in more Ross age material. Three anomalously young zircons (19.4± 0.9, 25± 0.9 and 23.1± 0.5) were found at the head of the Scott Glacier from Mt. Howe (MH). All of the Ross Sea samples contain age populations consistent with the Ross Orogeny; however the samples show spatial variability in the age distribution of the Mesozoic grains. The Central Eastern and Eastern Ross Sea has a ~100 Ma population which is consistent with the age populations seen at Kamb and Bindschadler Ice Streams. This suggests that the ice flow of the West Antarctic Ice Sheet (WAIS) was confined to the region during the Last Glacial Maximum (LGM). The Ross Sea also displays a spatial geographic boundary at the 170° with the presence of polymict rich till, as well as clay type (smectite and illite). More research needs to be done in order to determine the significance of the clay type with respect to polymict formation and preservation. Kathy Licht, PhD vi TABLE OF CONTENTS INTRODUCTION .............................................................................................................. 1 Physical Setting............................................................................................................... 2 Geologic History............................................................................................................. 4 East Antarctica............................................................................................................ 4 Transantarctic Mountains............................................................................................ 5 West Antarctica........................................................................................................... 8 Summary of Geologic Setting......................................................................................... 9 PREVIOUS RESEARCH ................................................................................................. 11 METHODS ....................................................................................................................... 13 Sample Acquisition....................................................................................................... 13 Detrital Zircon Separation............................................................................................. 13 U-Th-Pb Analysis ......................................................................................................... 14 U-Th/He Analysis ......................................................................................................... 16 Sand Petrography Analysis........................................................................................... 17 Particle Size Analysis ................................................................................................... 18 RESULTS ......................................................................................................................... 20 East Antarctica.............................................................................................................. 20 Particle Size .............................................................................................................. 20 Sand Petrography...................................................................................................... 20 U-Th-Pb .................................................................................................................... 21 West Antarctica............................................................................................................. 22 Particle Size .............................................................................................................. 22 Sand Petrography...................................................................................................... 22 U-Th-Pb .................................................................................................................... 23 Ross Sea and RISP........................................................................................................ 23 Particle Size .............................................................................................................. 23 Sand Petrography...................................................................................................... 23 U-Th-Pb .................................................................................................................... 24 Between Site Kolmogorov-Smirnov Analysis.............................................................. 24 U-Th/He Analysis ......................................................................................................... 25 DISCUSSION................................................................................................................... 27 What
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