Portland State University PDXScholar Dissertations and Theses Dissertations and Theses Winter 2-24-2016 Field Geology and Petrologic Investigation of the Strawberry Volcanics, Northeast Oregon Arron Richard Steiner 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 Steiner, Arron Richard, "Field Geology and Petrologic Investigation of the Strawberry Volcanics, Northeast Oregon" (2016). Dissertations and Theses. Paper 2712. https://doi.org/10.15760/etd.2708 This Dissertation 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]. Field Geology and Petrologic Investigation of the Strawberry Volcanics, Northeast Oregon by Arron Richard Steiner A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Environmental Sciences and Resources: Geology Dissertation Committee: Martin J. Streck, Chair Michael L. Cummings Jonathan Fink John A.Wolff Dirk Iwata-Reuyl Portland State University 2016 © 2015 Arron Richard Steiner i ABSTRACT The Strawberry Volcanics of Northeast Oregon are a group of geochemically related lavas with a diverse chemical range (basalt to rhyolite) that erupted between 16.2 and 12.5 Ma and co-erupted with the large, (~200,000 km3) Middle Miocene tholeiitic lavas of the Columbia River Basalt Group (CRBG), which erupted near and geographically surround the Strawberry Volcanics. The rhyolitic lavas of the Strawberry Volcanics produced the oldest 40Ar/39Ar ages measured in this study with ages ranging from 16.2 Ma to 14.6 Ma, and have an estimated total erupted volume of 100 km3. The mafic and intermediate lavas of the Strawberry Volcanics include both tholeiitic and calc-alkaline compositions; calc-alkaline andesite is the dominant type by volume. 40Ar/39Ar ages of the mafic and intermediate lava flows range from 15.6 Ma to 12.5 Ma, and volume estimates of the intermediate lavas are approximately 1,100 km3. The magmas that gave rise to the Strawberry Volcanics traveled to the surface through numerous dikes, some of which have been exposed at the surface and supplied lava to fissure – style eruptions and/or shield volcanoes. Herein, we show that the Strawberry Volcanics are related to the CRBG in both time and space and share a chemical affinity, specifically to the Steens Basalt. Chemical similarities are observed in normalized trace element patterns, selected trace element ratios, and radiogenic isotopes. Comparison of the Strawberry Volcanic rhyolites to the other Middle Miocene rhyolites of eastern Oregon associated with the initiation of the Yellowstone – Snake River mantle plume reveals similar eruption ages, trace element compositions, including the rare earth elements (REEs), and “A-type” ii rhyolite characteristics. These data suggest that the Strawberry Volcanics are part of the regional volcanism (basalt to rhyolite) of the Columbia River Basalt Province. The petrogenesis of the Strawberry Volcanics can be explained as follows: 1) The tholeiitic, intermediate magmas were produced by fractional crystallization of mafic magmas, which have a commonality with the surrounding Columbia River Basalt Group; 2) The calc-alkaline magmas are a result of mixing between tholeiitic basalt, rhyolite, and crust. The arc-like signature of the calc-alkaline lavas (elevated large ion lithophiles) is a result of both the melting source region and the end-members with which the mafic magmas mixed/contaminated. Other authors have produced similar findings from within the Basin and Range/Oregon-Idaho graben and CRB province. The difference at the Strawberry Volcanics is that there is no need for a primitive calc-alkaline magma or extensive fractional crystallization to generate the calc-alkaline andesite series. Alternatively, the calc-alkaline magmas of the Strawberry Volcanics were generated by a more primitive tholeiitic magma than erupted at the surface, which interacted with crustal melts and assimilated crustal lithologies from the complex zone of assimilated terranes that make up the basement of eastern Oregon. iii ACKNOWLEDGMENTS The author would like to express a sincere appreciation of gratitude to the academic committee members: Martin Streck, Michel Cummings, Jonathan Fink, John Wolff and Dirk Iwata-Reuyl. I would like to further thank Martin Streck for providing opportunities to study at Portland State University and working tirelessly with me on edits for this dissertation. The work for Chapters 1, 2 and 3 were supported by: NSF-EAR grant #1220676; PSU Faculty Enhancement grant to Streck; and 2011 GSA research grant # 9579-11. I would also like to thank Mark Ferns for our discussions of eastern Oregon geology, Richard M. Conrey, Charles M. Knaack and Scott Boroughs at Washington State University for their assistance in whole rock geochemical XRF and ICP-MS analysis; Frank Ramos at New Mexico State University for Isotope analysis, Frank Tepley and Dale Burns at Oregon State University for the EMP analysis, Bob Duncan, Anthony Koppers and Dan Miggins for age analysis at Oregon State University, Dale Burns for his thoughtful insights, excellent field company and stimulating conversation regarding this research and including all geology. And to Ashley Van Hoose/Steiner, thanks for excellent field assistance and superior editing and comments along the way. Thank you for supporting me in every way. I would also like to thank Eric Christiansen and Esteban Gazel for their comments and edits that helped to improve the final published manuscript of Chapter 1, along with Arturo Gomez-Tuena for his editorial handling and additional comments towards the publishment of Chapter 1. Lastly, I would like to thank my family. Without their love and support this could not have happened. Thank You. iv TABLE OF CONTENTS ABSTRACT ................................................................................................................... i ACKNOWLEDGMENTS ............................................................................................. iii LIST OF TABLES ......................................................................................................... viii LIST OF FIGURES ....................................................................................................... x Chapter 1. THE STRAWBERRY VOLCANICS: GENERATION OF ‘OROGENIC’ ANDESITES FROM THOLEIITE WITHIN AN INTRA-CONTINENTAL VOLCANIC SUITE CENTERED ON THE COLUMBIA RIVER FLOOD BASALT PROVINCE, USA. .............................................................................. 1 Abstract ................................................................................................................. 1 Introduction ........................................................................................................... 3 Methods ................................................................................................................ 5 Results ................................................................................................................... 7 Stratigraphy and New Ages of the Strawberry Volcanics ............................. 7 Field Relationships................................................................................. 7 40Ar/39Ar Ages of Strawberry Volcanics and Stratigraphic Relationships to Mid-Miocene Flood Basalts and Other Regional Rock Units ............... 10 Geochemistry ................................................................................................. 11 Tholeiitic Lavas of the Strawberry Volcanics ....................................... 11 The Calc-Alkaline Suite of the Strawberry Volcanics ........................... 13 Compositional difference between tholeiitic and calc-alkaline suite .... 14 Discussion ............................................................................................................. 15 Field Interpretations ....................................................................................... 15 Common Parent for Calc-Alkaline and Tholeiitic Magmas .......................... 18 Compositional Changes and Petrogenesis Associated with Calc-Alkaline and Tholeiitic Evolution ....................................................................................... 20 Implications for Other Intra-Continental Settings with Calc-Alkaline Suites 21 Conclusion ............................................................................................................ 24 v 2. THE VOLUMINOUS AND COMPOSITIONALLY DIVERSE, MID-MIOCENE STRAWBERRY MOUNTAIN VOLCANICS OF NORTHEASTERN OREGON AND THEIR RELATIONSHIPS TO BASALTIC AND RHYOLITIC VOLCANISM OF THE COLUMBIA RIVER BASALT PROVINCE. .............. 26 Abstract ................................................................................................................. 26 Introduction ........................................................................................................... 28 Geologic Setting ................................................................................................... 30 Accreted Terranes (~320-220 Ma)................................................................. 30 Clarno/John Day (~54-22 Ma) ......................................................................