ZIRCON GEOCHEMISTRY AND GEOCHRONOLOGY OF THE SEVEN DEVILS MOUNTAINS, WESTERN IDAHO: TESTING PROPOSED TIES TO THE WRANGELLIA TERRANE A THESIS SUBMITTED TO THE GRADUATE SCHOOL IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE MASTER OF SCIENCE BY HEATHER CASARES DR. KIRSTEN NICHOLSON- ADVISOR DEPARTMENT OF GEOLOGICAL SCIENCES BALL STATE UNIVERSITY MUNCIE INDIANA MAY 2019 Table of Contents Chapter 1 Overview……………………………………………………………………………….1 Introduction………………………………………………………………………………..1 Previous Work…………………………………………………………………………….3 Objectives and Significance……………………………………………………………….4 Chapter 2 Background…………………………………………………………………………….6 Tectonics of Western North America……………………………………………………..6 Geologic Setting………………………………………………………………………..….9 The Blue Mountains Province…………………………………………………………….9 Wallowa terrane Seven Devils Group…………………………………………………..10 Baker terrane………………………………………………………………………….…13 Izee terrane………………………………………………………………………….…..13 Olds Ferry terrane……………………………………………………………………….13 Wrangellia…………………………………………………………………………….….14 Chapter 3 Analytical Methods…………………………………………………………..……….17 Sample Collection………………………………………….…………………………….17 Thin Section Preparation…………………………………………………………………19 Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) Analysis…………………………………………………………………………………..19 X-ray Fluorescence spectrometry (XRF) Analysis…………………………………..…..21 Chapter 4 Manuscript………………………………………………………………………….....24 Acknowledgements………………………………………………………………………………49 References………………………………………………………………………………………..50 Appendix……………………………………………………………………………………...….59 i List of Tables Table A-1: U-Pb dating and of zircons from this study using LA-ICPMS…………………..…68 Table A-2: In Situ Lu-Hf isotopic data of zircons from this study…………………………..…..72 Table A-3: Average εHf(t) and errors for the Seven Devils samples……………...…………….73 Table A-4: Loss on Ignition (LOI)…………………………………………………………….....73 Table A-5: Whole Rock Geochemistry for the Seven Devils terrane determined by XRF……..74 ii List of Figures Figure 1-1: Location of the Seven Devils Mountains in Western Idaho………………………….1 Figure 2-1: Arc-arc collision model of the Blue Mountains Province……………………………8 Figure 2-2: The Blue Mountains Province and locations of terranes……………………………10 Figure 2-3: Close up view of the Wallowa terrane and rocks…………………………………..11 Figure 2-4: The location of the Wrangellia terrane……………………………………………..16 Figure 3-1: Sample location map…………………………………………………………...……18 Figure A-1: Sample SD001………………………………………………………………………60 Figure A-2: Sample SD002………………………………………………………………………61 Figure A-3: Sample SD003………………………………………………………………………62 Figure A-4: Sample SD004………………………………………………………………………63 Figure A-5: Sample SD005………………………………………………………………………64 Figure A-6: Sample SD006………………………………………………………………………65 Figure A-7: Sample SD007………………………………………………………………………66 Figure A-8: Sample SD008………………………………………………………...…………….67 Figure A-9: Sample SD009………………………………………………………………………68 Figure A-10: Average U-Pb ages for sample SD004…………………………………………….70 Figure A-11: Average U-Pb ages for sample SD006…………………………………………….70 Figure A-12: Average U-Pb ages for sample SD007…………………………………………….71 Figure A-13: Average U-Pb ages for sample SD008………………………………………….…71 Figure A-14: Average U-Pb ages for sample SD009…………………………………………….72 Figure A-15: Volcanic Rock Diagram Using Immobile Trace Elements………………………..76 Figure A-16: Discriminate within-plate granites, volcanic arc granites & ocean ridge granites using Nb vs. Y…………………………………………………………………………...………76 iii Figure A-17: Discriminate within-plate granites, volcanic arc granites & ocean ridge granites using Rb vs. Nb+Y……………………………………………………………………………….77 iv Chapter One 1.1 Introduction The western part of North America preserves a rich tectonic history. The western margin of the North American Craton has many terrains and microcontinents that have accreted to it. The boundary between terranes is known as the suture zone. These terranes and microcontinents began forming during and after the breakup of Pangaea in the early Triassic (Murphy et al., 2009). The forces created by such massive movement allowed for changes in the plate boundaries which caused the Farallon plate to begin subducting off of North America (Sigloch and Mihalynuk, 2013). The process of subduction ultimately created much of the volcanic arc terranes and microcontinents that now form the North American Cordillera. Figure (1-1) Location map of the Seven Devils Mountains field study area from (Farag, 2018). 1 The Seven Devils Mountains (Figure 1-1) are located along a 70 km stretch on the eastern side of the Snake River in Western Idaho within an area known as Hells Canyon Wilderness by the town of Riggings, Idaho (Sarewitz, 1983). The Seven Devils Mountains consist of mostly intermediate to mafic igneous rocks with rare felsic rocks that have all been variably metamorphosed. These rocks are considered to be the easternmost exposure of Permian to Triassic volcanic rocks in the North American Cordillera (Vallier, 1977). Modern analytical tools and scientific understanding of trace element chemistry has improved significantly since the last study of the Seven Devils Mountains, conducted in the 1970s to the 1980s (Jones et al., 1977; Sarewitz, 1982). Conducting modern whole rock geochemical analysis including major and trace element geochemistry, and zircon U-Pb geochronology, will bring new insight on the formation of the Seven Devils, how volcanic arcs evolve over time, and importantly, how western North America has evolved. The North American Cordillera provides an excellent location to study terrane translation in an accretionary orogeny. Previous studies and speculations have provided the Baja B.C. (Baja-British Columbia) hypothesis of terrane transport (Champion et al., 1984; Umhoefer, 1987; Wyld and Wright, 2001; Wyld et al., 2006). Northward terrane transport in the Cordillera, such as the Wrangellia terrane, is supported by fault displacements and paleomagnetic data suggesting displacements from 1100 to 3000 km in Washington and the British Columbia (Champion et al., 1984; Wynne et al., 1995; Wyld et al., 2006). Trace element geochemistry, improved U-Pb geochronology, and Hf isotope analysis will allow a better understanding of the tectonic history of the terrane and test models for northward displacement of the arc, by allowing for robust comparisons with data from the Wrangellia terrane and the surrounding Blue Mountains terranes. If the Seven Devils terrane is indeed part 2 of the Wrangellia terrane, then collected data will provide additional evidence for significant long-range transport along the Cordilleran margin. If not, then the Seven Devils terrane may represent an independent tectonic element of the Cordillera that may not require orogenic displacement. 1.2 Previous Work The main terranes (Wallowa, Baker, Izee, and Olds Ferry) of the Blue Mountains Province formed as island arc systems along the continental margin of western Laurentia. The Wallowa terrane has been known by many names such as the “volcanic arc terrane”, “Wallowa Mountains–Seven Devils Mountains volcanic arc terrane” (Brooks and Vallier, 1978), and the “Seven Devils terrane” (Vallier, 1977). The Wallowa terrane is the most outboard from the continental margin and is an island arc terrane that formed in an intra- oceanic setting in the Blue Mountains Province (LaMaskin et al., 2008; 2011). The Seven Devils terrane, which has been interpreted to be part of the Wallowa terrane, and even the Wrangellia terrane, is a volcanic complex in what is now western Idaho. Vallier (1977) described the Seven Devils and identified four separate formations: The Permian Windy Ridge formation, Permian Hunsaker Creek formation, Triassic Wild Sheep Creek formation, and the Triassic Doyle Creek formation. The majority of the volcanic rocks in these formations were called spilite, keratophyre, and quartz keratophyre. They are now reclassified as metabasalt, meta-andesite, metadacite, and metarhyolite based on their greenschist metamorphic facies (Vallier et al. 2016). Previous work comparing the Seven Devils to Wrangellia includes paleomagnetic studies, comparative studies using fossils, and geochemistry. Several authors including Hillhouse et al. (1982) and Harbert et al. (1995) worked to provide evidence for the migration of the Wallowa and Wrangellia terranes using 3 paleomagnetism. The core samples collected for these studies include volcanoclastic sedimentary, sedimentary, and volcanic flow rocks. Paleomagnetic data provide inclination and declination information that yields a paleolatitude, as well as paleopole locations comparable to other data sets. The two studies from Hillhouse in 1982 and again in 1984 on the Wallowa and Wrangellia terranes respectively, provide a paleolatitude ranging from 10 to 18 degrees from the Late Triassic in either the northern or southern hemisphere. The studies also show that there had to have been some kind of rotation in the Seven Devils terrane in order to bring it to where it is present day (Hillhouse, 1984). Comparative fossil studies and the use of fossils were the main source for age dating the surrounding rocks. The Seven Devils terrane contains fossils in the Wild Sheep Creek formation. These fossils are concentrations of the bivalves Daonella degeeri and D. frami (Jones, 1977). These fossils resemble others in beds beneath the Nikolai Greenstone of the Wrangellia terrane in southern Alaska. The only other congeneric bivalves that resemble these two species are seen in only two other localities