Teleseismic imaging of the Slave craton and implications for the assembly of cratonic lithosphere by Chin-Wu Chen M.Sc., Geophysics, National Taiwan University, Taipei, Taiwan, 2000 B.Sc., Earth Science, National Central University, Chungli, Taiwan, 1998 Submitted to the Department of Earth, Atmospheric and Planetary Sciences in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the MASSACHUSETTS INSTITUTE OF TECHNOLOGY February 2010 ARCHIVES © Massachusetts Institute of Technology 2010. All rights reserved. MASSACHUSETTS INST TfUTE OF TECHNOLOGY MAY 0 5 2010 A uthor ................ ........................................... LIBRA R IES Department of Earth, Atmospheric and Planetary Sciences November 2, 2009 Certified by . ....... Stephane Rondenay Associate Professor of Seismology Thesis Supervisor A ccepted by ....................... )......................... Maria T. Zuber E.A. Griswold Professor of Geophysics Head, Department of Earth, Atmospheric and Planetary Sciences 2 Teleseismic imaging of the Slave craton and implications for the assembly of cratonic lithosphere by Chin-Wu Chen Submitted to the Department of Earth, Atmospheric and Planetary Sciences on November 2, 2009, in partial fulfillment of the requirements for the degree of Doctor of Philosophy Abstract In this dissertation, I investigate the assembly and evolution of the Archean cratonic litho- sphere by using two complementary seismological methods to image the lithospheric struc- ture of the Slave craton in Canada. First, I perform surface wave tomographic inversions to constrain the depth dependence of Rayleigh wave phase velocity, shear wave velocity, and azimuthal anisotropy of the Slave cratonic lithosphere. The tomographic images reveal high shear wave velocities associated with a particularly depleted, cold, and unperturbed Archean cratonic lithosphere. Furthermore, the inversions reveal distinct anisotropic do- mains in the crust, the lithospheric mantle, and the sub-lithospheric mantle. These results reflect the evolutionary history of the cratonic lithosphere. Secondly, I image seismic discon- tinuities in the lithosphere using receiver-function analysis of converted P-to-S waves. The resulting seismic profile shows a pronounced low velocity discontinuity at -100 km depth beneath the central Slave craton. This seismic discontinuity shows striking spatial corre- lation with both an electrical conductive anomaly derived from magnetotelluric sounding, as well as a petrologically-defined ultra-depleted layer. The synthesis of coincident seismic, electrical, and petrological evidence supports that this geophysical and petrological bound- ary represents a compositional interface marked by alteration minerals. I suggest that this mineralization resulted from relict metasomatism associated with an Archean subduction event, which played an important role in the assembly of the Slave craton. Finally, to im- prove the efficiency and automation of receiver function calculation and data preprocessing workflow, I develop an application of an array-conditioned deconvolution technique for effec- tively processing large amounts of seismic array data. I demonstrate that this technique is readily applicable to teleseismic array data. This technique is especially effective in turning noisy traces from earthquakes with smaller magnitudes into usable data. Thesis Supervisor: Stephane Rondenay Title: Associate Professor of Seismology 4 Acknowledgmentst I used to think that the acknowledgments section was the easiest part of the thesis to write. Reflecting upon the past six years of study and life at MIT, I find myself overwhelmed and humbled by all the help, support, and love I have received; it made this thesis possible and enriched my life so much that I don't know where to start expressing my gratitude. Now I realize writing acknowledgments is no easy task. I am deeply indebted to my advisor, Stephanie Rondenay. He bravely took me under his wing six years ago and convinced me that doing fieldwork is fun, when I wanted to be an armchair seismologist working on the core-mantle boundary. While my physical fitness was intensively challenged, I experienced some of the most memorable and unique moments in my life when in the field. Yes, the all-time favorite was seeing the Christmas-tree-like lights from the GMC Yukon after snowshoeing for hours on the darkened Big Skidder Hill in Washington State. He showed me how doing serious science does not have to conflict with enjoying life, when we relaxed with a beer in the Black Knight Pub in Yellowknife after a long day, sampled whisky in snow-stormed Seattle before embarking on a tough field season, or jumped into the glassy Aegean Sea under the Mediterranean sunshine after rushing through narrow streets on the island of Syros to retrieve a seismic station. I hold these memories dear. Stdphane's encouragement and infinite patience were instrumental in the completion of this dissertation. I would not have come this far without his insight, openness, generosity, and sense of humor. He taught me to be meticulous on details yet always keep the big picture in mind. His enthusiasm is contagious. His deep knowledge of seismological techniques and broad interests in earth sciences led the multi-disciplinary approach in my research. He has more than the characteristics needed to be a successful scientist and mentor; he is a genuinely good guy and good friend. I hope this thesis marks not the end but a continuation of our collaboration and friendship. Sam Bowring was my second general project advisor and my thesis committee chair. He I sty (1'*andv Ires1(ea(Irch (Ie suppolted by a;I n MIT i sPreiden t ial Fel lship an(d Nationl Science F(mdatin grants EAR-04090aUd EAR-0544996. broadened my horizons by stimulating me to explore the geological and geochemical aspects of the Slave craton and the evolution of the Earth in general. The breadth and depth of his knowledge is unparalleled. And lie never wears a bug net in the field! He was also a most serious and generous reader, offering insightful comments and discussions along the way, which reshaped my understanding of craton assembly. I started working with Doug Miller during my 2008 summer internship at Schlumberger- Doll Research, on the deconvolution project that eventually became an important part of my thesis. Working with Doug has been a privilege and a pleasure. His mathematical insight always pointed to the core of a problem. I appreciate very much the many afternoons we spent in front of the computer scratching our heads over the behavior of the wiggles. I also enjoyed the Shakespeare and lute songs lie introduced me to. Doug is a sincere mentor and the ideal of a curious, enthusiastic, and versatile scientist. I look forward to the opportunity of future continued collaboration. I owe much appreciation to Hugues Djikpesse, whom I first met at the career fair at MIT. He later offered me the internship at SDR and was an effective and caring supervisor, always ready to help. His thoughtful suggestions greatly improved the clarity of our paper. I also thank Jakob Haldorsen for his help with my presentation, insightful discussions on deconvolution, and heartfelt support and encouragement. Many thanks to Rob van der Hilst for his helpful suggestions that improved my thesis. He always welcomed my questions and gave useful advice. Thanks also go to Alison Malcolm. I benefitted much from her stimulating questions on my work. David Snyder is the co-leader of our fieldwork in the Slave province. I learned much from his intensive experience in the field and in logistics management. His input to our papers and open-minded discussion of new ideas are much appreciated. I thank Rob Evans for the exciting collaboration on the comparison of receiver function image and the magnetotelluric model. His input was critical to this work. Thanks also go to Wiki Royden for her help on my second general project, Lindy Elkins-Tanton for helpful discussion on melting of basalt, and Nafi Toks6z for his encouragement. Science becomes more fun when you are not doing it alone. In my first few years of Ph.D. study, I was fortunate to interact with the seismology group at Brown University. Dayanthie Weeraratne and Yingjie Yang generously spent much time helping me understand and run the surface wave inversion. Dayanthie keeps sharing with me her thoughts and experience regarding research and life. Occasional consultation with Donald Forsyth and Aibing Li were also appreciated. In addition, I thank Sonja Aulbach, Max Moorkamp, Fiona Darbyshire for sharing their results with me, John Carson and Peter Holman of Gelogical Survey of Canada for giving me access to the Slave craton radiometric data, and Laura Mackenzie and Zhu Zhang for their help with Antelope and Cascadia dataset. The big family of students and postdocs in EAPS is an amazing source of support and friendship. In particular, I thank Huajian Yao for his last minute and generous help with the neighborhood algorithm and many discussions on surface waves, Fred Pearce for sharing stimulating ideas and his codes, Lili Xu for helping me get started with receiver functions, Jenny Suckale for the wonderful adventure in Greece, Xander Campman for his pleasant com- pany in the Slave, Ping Wang and Chang Li for many discussions and help on seismology in general, and everyone above for numerous fun conversations. I thank Einat Lev, Erwan Mazarico, James Dennedy-Frank, Sarah Johnson, and Krystle Catalli for being awesome officemates