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Areal Extent and Volumes of the Dinner Creek Tuff Units, Eastern Oregon Based on Lithology, Bulk Rock Composition and Feldspar Mineralogy

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Areal Extent and Volumes of the Dinner Creek Tuff Units, Eastern Oregon Based on Lithology, Bulk Rock Composition and Feldspar Mineralogy Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Winter 4-10-2018 Areal Extent and Volumes of the Dinner Creek Tuff Units, Eastern Oregon Based on Lithology, Bulk Rock Composition and Feldspar Mineralogy Teresa Rae Hanna Portland State University Follow this and additional works at: https://pdxscholar.library.pdx.edu/open_access_etds Part of the Geology Commons, and the Volcanology Commons Let us know how access to this document benefits ou.y Recommended Citation Hanna, Teresa Rae, "Areal Extent and Volumes of the Dinner Creek Tuff Units, Eastern Oregon Based on Lithology, Bulk Rock Composition and Feldspar Mineralogy" (2018). Dissertations and Theses. Paper 4346. https://doi.org/10.15760/etd.6239 This Thesis is brought to you for free and open access. It has been accepted for inclusion in Dissertations and Theses by an authorized administrator of PDXScholar. Please contact us if we can make this document more accessible: [email protected]. Areal Extent and Volumes of the Dinner Creek Tuff Units, Eastern Oregon Based on Lithology, Bulk Rock Composition and Feldspar Mineralogy by Teresa Rae Hanna A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science in Geology Thesis Committee: Martin J. Streck, Chair Robert Perkins John Bershaw Portland State University 2018 ABSTRACT The Dinner Creek Tuff erupted during a period of rhyolitic volcanism coeval to the flood volcanism associated with the Columbia River Basalt Group. The High Rock Caldera Complex, Lake Owyhee and McDermitt volcanic fields account for ~90% of the rhyolites erupted between 16.7-15.0 Ma. Situated at the northern end of the Lake Owyhee volcanic field, the Dinner Creek Tuff was originally mapped as a ~2,000 km2 single ignimbrite confined to the Malheur Gorge. Streck et al. (2015) correlated tuff outcrops previously mapped as generic Miocene welded tuff as well as local units such as the “Mascall” or “Pleasant Valley” tuff of eastern Oregon to individual cooling units that comprise the newly redefined Dinner Creek Tuff, enclosing an area of ~25,000 km2. Areal extents defined in this study show that all outcrops now determined to be Dinner Creek Tuff enclose an area of ~31,800 km2 not including any fallout deposits that likely extended beyond the defined area. Although Dinner Creek Tuff rhyolites have nearly identical compositions, different ages and subtle geochemical and mineralogical differences exist and were used to divide the Dinner Creek Tuff into four discrete cooling units. Except for unit 4, the units are lithologically very similar. Unit 1 is the Dinner Creek Tuff unit associated with the Malheur Gorge type section. The four cooling units have ages of 16.15-16 Ma (unit 1), 15.6-15.5 Ma (unit 2), 15.46 Ma (unit 3) and 15.0 Ma (unit 4). Areal extents were established for all four cooling units based on feldspar compositions along with lithological and bulk rock geochemical data. Minimal extents of individual units are as follows: ~22,590 km2 (unit 1), ~17,920 km2 (unit 2), ~14,170 km2 i (unit 3) and ~8,370 km2 (unit 4). Using conservative thicknesses, determined erupted tuff volumes are ~170 km3 (unit 1), ~125 km3 (unit 2), ~99 km3 (unit 3) and ~46 km3 (unit 4), totaling ~440 km3 and dense rock equivalents are ~152 km3 (unit 1), ~96 km3 (unit 2), ~76 km3 (unit 3) and ~31 km3 (unit 4), totaling ~356 km3. These extents and volumes are the absolute minimum based solely on the locations of exposed tuff sections and the inclusion of the source. Centering eruptive units on source areas where they are known, expands the tuff extents into a more radial pattern as would be expected for low-aspect ratio, high energy ash-flow tuff eruptions. These probable extents increase the areal extents of the individual units to: ~36,900 km2 (unit 1), ~31,660 km2 (unit 2), ~17,290 km2 (unit 3) and ~10,150 km2 (unit 4) distributed over a ~43,490 km2 area. Likewise, erupted tuff volume and dense rock equivalents also increase: volume— ~277 km3 (unit 1), ~222 km3 (unit 2), ~121 km3 (unit 3) and ~56 km3 (unit 4); DRE— ~248 km3 (unit 1), ~170 km3 (unit 2), ~93 km3 (unit 3) and ~38 km3 (unit 4). New mapping confirms previous hypotheses that the Castle Rock caldera erupted unit 1 and identified the new Ironside Mountain caldera as the source for unit 2 while precise source areas for unit 3 and 4 are not yet known but are thought to lie within the Dinner Creek Eruptive Center. Minimal calculated caldera volumes for units 1 and 2 are ~98.5 km3 (unit 1) and ~31.1 km3 (unit 2). Adding the thick ponded intra caldera tuff volume to the determined and probable erupted tuff volumes determined in this study, increases the erupted volumes to ~268 km3 (determined) and ~375 km3 (probable) for unit 1 along with ~157 km3 (determined) and ~253 km3 (probable) for unit 2. DREs ii increase to ~251 km3 (determined) and ~347 km3 (probable) for unit 1 along with ~128 km3 (determined) and ~202 km3 (probable) for unit 2. iii ACKNOWLEDGEMENTS I would like to thank my advisor Martin Streck for his expertise, guidance and patience as well as my committee—Martin Streck, John Bershaw and Robert Perkins for their time and efforts reviewing my work. This study was possible due to support from the National Science Foundation grant EAR-1551495 to Martin Streck. I greatly appreciate the work of my fellow graduate and undergraduate students that providing geochemical data and/or samples used in in this study. Lastly, I would like to thank my family and friends for their continued support and encouragement throughout my academic career. iv TABLE OF CONTENTS Abstract ................................................................................................................................ i Acknowledgements ............................................................................................................ iv List of Tables ..................................................................................................................... ix List of Figures ......................................................................................................................x List of Abbreviations ..................................................................................................... xviii Introduction ..........................................................................................................................1 Background ..........................................................................................................................6 Geologic Setting ...............................................................................................................6 Blue Mountain Province and Accreted Terranes ..........................................................6 Wallowa Terrane ......................................................................................................7 Olds Ferry Terrane ...................................................................................................8 Baker Terrane...........................................................................................................9 Izee Terrane ...........................................................................................................10 Columbia River Basalt Group ....................................................................................10 Rhyolitic Volcanism ...................................................................................................12 Lake Owyhee Volcanic Field.................................................................................13 McDermitt Volcanic Field .....................................................................................14 High Rock Caldera Complex .................................................................................15 Snake River Plain/Yellowstone Hotspot Trend .....................................................16 Oregon-Idaho Graben .................................................................................................18 Dinner Creek Tuff ......................................................................................................20 v Methods..............................................................................................................................25 Sample Selection ............................................................................................................25 Chemical Analysis and Unit Designation ......................................................................26 Sample Preparation .....................................................................................................26 Electron Microprobe Analysis ....................................................................................26 Unit Designation .........................................................................................................27 Mapping .........................................................................................................................27 Tuff Volumes and Dense Rock Equivalent ....................................................................28 Results ................................................................................................................................30 Unit Designation ............................................................................................................30 Feldspar Crystal EMP Analysis..................................................................................30 Units 3 and 4 ...............................................................................................................34
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