Age, Origin, and Tectonic Evolution of the Yellow Aster Complex: Northwest Washington State
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Western Washington University Western CEDAR WWU Graduate School Collection WWU Graduate and Undergraduate Scholarship 2014 Age, origin, and tectonic evolution of the Yellow Aster Complex: northwest Washington state Eric A. (Eric Adam) Hoffnagle Western Washington University Follow this and additional works at: https://cedar.wwu.edu/wwuet Part of the Geology Commons Recommended Citation Hoffnagle, Eric A. (Eric Adam), "Age, origin, and tectonic evolution of the Yellow Aster Complex: northwest Washington state" (2014). WWU Graduate School Collection. 356. https://cedar.wwu.edu/wwuet/356 This Masters Thesis is brought to you for free and open access by the WWU Graduate and Undergraduate Scholarship at Western CEDAR. It has been accepted for inclusion in WWU Graduate School Collection by an authorized administrator of Western CEDAR. For more information, please contact [email protected]. AGE, ORIGIN, AND TECTONIC EVOLUTION OF THE YELLOW ASTER COMPLEX: NORTHWEST WASHINGTON STATE By Eric A. Hoffnagle Accepted in Partial Completion of the Requirements for the Degree Master of Science Kathleen L. Kitto, Dean of Graduate School ADVISORY COMMITTEE Chair, Dr. Elizabeth R. Schermer Dr. Edwin H. Brown Dr. Bernard A. Housen MASTER’S THESIS In presenting this thesis in partial fulfillment of the requirements for a master’s degree at Western Washington University, I grant to Western Washington University the non‐exclusive royalty‐free right to archive, reproduce, distribute, and display the thesis in any and all forms, including electronic format, via any digital library mechanisms maintained by WWU. I represent and warrant this is my original work, and does not infringe or violate any rights of others. I warrant that I have obtained written permissions from the owner of any third party copyrighted material included in these files. I acknowledge that I retain ownership rights to the copyright of this work, including but not limited to the right to use all or part of this work in future works, such as articles or books. Library users are granted permission for individual, research and noncommercial reproduction of this work for educational purposes only. Any further digital posting of this document requires specific permission from the author. Any copying or publication of this thesis for commercial purposes, or for financial gain, is not allowed without my written permission. Eric A. Hoffnagle June 1, 2014 AGE, ORIGIN, AND TECTONIC EVOLUTION OF THE YELLOW ASTER COMPLEX: NORTHWEST WASHINGTON STATE A Thesis Presented to the Faculty of Western Washington University In Partial Fulfillment of the Requirements for the Degree Master of Science By Eric A. Hoffnagle June 2014 ABSTRACT The Yellow Aster Complex in northwest Washington is a basement portion of the Chilliwack composite terrane and appears throughout the western foothills of the North Cascades as fault bounded tectonic blocks (Brown, 1987; Brown et al. 2010). This study was undertaken in part to refine and understand the significance of the depositional, magmatic, and metamorphic history of the Yellow Aster Complex. Field work and petrographic analyses reveal that the Yellow Aster Complex consists of calc-silicate and quartzo-feldspathic paragneisses with minor amounts of marble and quartzite. Leucocratic and mafic intrusions are also present throughout the terrane. Zircons from six Yellow Aster Complex samples were dated using U-Pb in order to evaluate the detrital provenance of the terrane. Sampling was conducted at two areas: Schriebers Meadow and Yellow Aster Butte. Two meta- sedimentary samples (YA-5, EAH-39) contain a range of Mesoproterozoic to Archean detrital zircon ages and younger grains from the Early Paleozoic. Sample YA-5 has two young peaks at 417 ± 3 Ma and 402 ± 7 Ma, while EAH-39 has a broad peak at ~428 Ma. Two other quartzose calc-silicate paragneisses have peak ages of 409 ± 5 (EAH-10b), 405 ± 4 Ma (EAH-11), and 386 ± 5 Ma (EAH-11). Sample EAH-03 is a pyroxene calc-silicate paragneiss with peak ages of 403 ± 8 Ma and 389 ± 6 Ma. Samples EAH-39 and YA-5 contain zircon ages within the North American magmatic gap (1.61-1.49 Ga) and Early Paleozoic (500-400 Ma) which are not consistent with ages from western North America, but rather similar to Baltica and the exotic Early Devonian Karheen Formation (Alexander terrane; northwest British Columbia – southeast Alaska). Peak ages from samples EAH-03, - 10b and -11 are thought to be from grains locally derived from magmatic sources. Previous iv work (Brown et al. 2010) concluded that the Yellow Aster Complex has similarities to parts of the Yukon-Tanana terrane, which has a western Laurentian affinity. Characteristics of detrital zircon populations with a western Laurentian affinity include a significant number of 1800 Ma grains, no grains from the North American magmatic gap, and few grains younger than 1000 Ma. In addition, Brown et al. (2010) identified two intrusions with ages of 418 Ma and 409 Ma, and suggested the occurrence of a pre-418 Ma metamorphic event. Based on the new detrital zircon ages of this study, the Yellow Aster Complex experienced sedimentation after 418 Ma and metamorphism after 386 Ma. The overall geology, paired with new zircon ages, suggests that the Yellow Aster Complex may have evolved from both Baltic and western Laurentia sourced detritus. This study also concludes that Baltic and western Laurentian sources preserved in the Yellow Aster Complex may have been caused by terrane amalgamation or sharing of a depositional basin prior to the formation of younger components of the Chilliwack composite terrane. v ACKNOWLEDGEMENTS I am very grateful for multiple people and institutions that made this project possible. First off, many thanks to my academic and thesis advisor, Dr. Liz Schermer, who accepted me for graduate work at Western Washington University. Liz is a remarkable geologist and writer who has greatly improved my scientific and writing skills. I’m also very thankful for her patience and guidance. The idea for this project came from Dr. Edwin “Ned” Brown who has spent many years unraveling the tectonic history of western Washington. I feel very fortunate to have worked with Ned on this exciting project, and I’m thankful for his time and knowledge he shared with me. Thank you to committee member and Department Chair, Dr. Bernie Housen, who provided additional comments and critiques that strengthened this thesis. I’d also like to thank the entire faculty and staff of the Geology Department for helping me achieve my academic goals. It would be a shame if George Mustoe were not mentioned. George has probably helped each graduate student somehow during his tenure at Western. Specifically, I admire George’s quick action to try and save a dropped zircon sample. Funding for this project was made possible by the WWU Research and Sponsored Programs, the WWU Geology Department, and the Geological Society of America. Special thanks to the Arizona Laserchron Center and Ned Brown for refining and mounting the final zircon separations. Thank you to Ned and his wife, Linda, for their hospitality while in Tucson. Thanks to my field assistants, Brandon Brayfield and Austin Hart, who helped break down and carry samples from the field. I’m very grateful for the friends in the Department who have all offered overwhelming support. I wish them all the very best in their future endeavors. My parents, Chuck and Sharon, have been very supportive of my academic and vi career decisions, and I feel so fortunate to have them. Thank you to my brother, Carl, for the ambition he bestows in me. I would also like to thank the Weaver family for their support. Most of all, I thank my wonderful wife and best friend, Meghan. She helped me so much throughout graduate school, and I couldn’t have done this without her everlasting love. vii TABLE OF CONTENTS ABSTRACT ............................................................................................................................. iv ACKNOWLEDGMENTS ....................................................................................................... vi LIST OF FIGURES ................................................................................................................. xi LIST OF TABLES ................................................................................................................. xiii INTRODUCTION .....................................................................................................................1 GEOLOGIC SETTING .............................................................................................................6 A. Laurentia in the Paleozoic ...............................................................................6 B. Northwest Washington ....................................................................................7 STATEMENT OF THE PROBLEM .........................................................................................9 PREVIOUS WORK - YELLOW ASTER COMPLEX ...........................................................10 METHODS AND PROCEDURES..........................................................................................13 FIELD SITE GEOLOGY - SCHRIEBERS MEADOW .........................................................17 PETROGRAPHY - SCHRIEBERS MEADOW .....................................................................31 A. Quartzose Calc-Silicate Gneiss ......................................................................31 B. Pyroxene Calc-Silicate Gneiss .......................................................................31