MARGINAL DEPOSITS OF MAAR VOLCANOES IN THE FIRST FLAT MESA AREA, HOPI BUTTES VOLCANIC FIELD, NAVAJO NATION, ARIZONA by Mallory Zelawski A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science in Geology Northern Arizona University August 2011 Approved: ______________________________ Michael H. Ort, Ph.D., Chair ______________________________ Nancy R. Riggs, Ph.D. ______________________________ George Billingsley, USGS ______________________________ Margaret Hiza, Ph.D., USGS i ABSTRACT MARGINAL DEPOSITS OF MAAR VOLCANOES IN THE FIRST FLAT MESA AREA OF THE HOPI BUTTES VOLCANIC FIELD, NAVAJO NATION, ARIZONA MALLORY ZELAWSKI The late Miocene-Pliocene Hopi Buttes volcanic field contains at least 300 maar and diatreme features in an area of 1800 km2. Phreatomagmatic explosions involved the interactions of monchiquitic to nephelinitic magma with groundwater, lake water, or liquiefied sediments from the underlying Bidahochi Formation. These maars produced craters within the underlying strate that then increased in size due to subsidence of unstable crater walls. The field relations between marginal deposits, maar crater deposits, and country rock both inside and outside of the crater link deformation of sediments with processes occurring during and due to an eruption. At least 23 vents are exposed within approximately 51 km2 of the First Flat Mesa area in the north-central Hopi Buttes. Locally these vents provide well- preserved exposures of marginal deposits, maar crater deposits, and country rock. These units provide critical geologic constraints regarding the vertical and lateral facies changes that occur proximal to the vent. Ten volcanic facies, three limestone facies, and one marl facies have been described and provide spatial and temporal information about processes and interactions that occur within and adjacent to the vent during a phreatomagmatic eruption. A majority of these facies suggest magma interaction with water-saturated ii sediment which created explosive eruptions that produced juvenile lapilli, blocks and bombs, and clasts of country rock that were recycled within the vent or dispersed away from the vent by base surges or fallout. These consist of massive lapilli tuff to moderately bedded lapilli tuff that typically contains blocks and bombs up to 2-3 meters. Where vents occur within close proximity, saturated sediments filling one crater may break the wall between them and slump from one vent into the neighboring vent as it is erupting. Some eruptions began phreatomagmatically, used up the available water, and became magmatic, producing scoria deposits that filled in the craters. Crater-lake facies suggest that most of the material removed by the eruption was deposited outside of the crater, allowing water to fill the crater and deposit limestone. Crater-lake facies are not found in vents where scoria deposits are found, although occasionally lapilli and ash are found within the limestone, from a nearby vent eruption and depositing volcanic material into the lake. Facies descriptions and interpretations provided information used to produce an eruptive model for the vents within the study area. iii ACKNOWLEDGEMENTS I would like to thank my committee members: Michael Ort, Nancy Riggs, George Billingsley, and Margaret Hiza-Redsteer for all of their support, advice, and knowledge. I would also like to thank Tom Hoish for the use of his microscope camera and Larry Middleton for helping me with thin sections descriptions. In addition, I would like to thank Piero Dellino and Tony Maria for all of their input and help with Image and fraccalc. I thank all of those who helped me out with field work through the hot summers: Matt Sagi, Aaron Wonders, Megan Beach, Byron Charley, Lang Suby, Tyler Brown, Courtney Silverberg, Sean Rudzitis, and Phil Lindner. Thank you to all of my friends who were there to listen, provide advice, and distractions when necessary. I would like to give a special thanks to my family. My parents have provided support, both emotional and financial, throughout my education. Without their help there is no way that I would have been able to complete this adventure. They have supported me in everything that I have done, and I appreciate all they have done for me through the years. Support for this thesis was provided by the U. S. Geological Survey, National Cooperative Geologic Mapping Program, under USGS award number G09AC00135. The views and conclusions contained in this document are those of the authors and should not be interpreted as necessarily representing the official policies, either expressed or implied, of the U. S. Government. Additional funding for this thesis was provided by the Four Corners Geological Society, Tom and Rose Bedwell Physical Sciences Scholarship, Pioneer Natural Resources Research Grant, and Friday Lunch Clubbe. The Navajo Nation Minerals Department graciously provided permission to work iv in Tsézhin bii‟. Any persons wishing to conduct geologic investigations on the Navajo Nation must first apply for and receive a permit from the Navajo Nation Minerals Department, P.O. Box 9000, Window Rock, AZ 86515. I would like to thank the White Cone Chapter and the families around the First Flat Mesa area for their hospitality and friendliness. In particular I would like to thank Francis Lester, Sally Ann Dick and their family for their incredible generosity, advice, and friendship in allowing me to become a part of their family. v TABLE OF CONTENTS ABSTRACT ………………………………………………………………………….....ii ACKNOWLEDGEMENTS……………………………………………………………iv TABLE OF CONTENTS…………………………………..…………………………..vi LIST OF TABLES……………………………………………………………………...ix LIST OF FIGURES……………………………………………………………………..x LIST OF PLATES……………………………………………………………………...xii CHAPTER 1. INTRODUCTION AND BACKGROUND…………………………..1 INTRODUCTION……………………………………………………………………….1 TECTONOMAGMATIC SETTING…………………………………………………….2 Colorado Plateau…………………………………………………………………2 Hopi Buttes volcanic field……………………………………………………….5 Study Area……………………………………………………………………….9 PHREATOMAGMATISM……………………………………………………………...10 Maar volcanoes…………………………………………………………………..14 Magma-water interactions……………………………………………………….17 Particle morphology analysis…………………………………………………….24 Marginal deposits………………………………..……………………………....26 PURPOSE AND OBJECTIVES………………………………………………………...27 CHAPTER 2. FIELD UNITS…………….……………………………………………29 INTRODUCTION……………………………………………………………………….29 UNIT DESCRIPTIONS………………………………………………………………….30 Quaternary units...………………………………………………………………..31 vi Tertiary units……………………………………………………………………33 Tertiary volcanic rocks………………………………………………………….34 CHAPTER 3. FACIES DESCRIPTIONS AND INTERPRETATIONS…………..59 INTRODUCTION……………………………………………………………………...59 FACIES DESCRIPTIONS/INTERPRETATIONS…………………………………….60 Facies LT 1………………………………………………………………………60 Facies LT 2………………………………………………………………………61 Facies LT 3………………………………………………………………………63 Facies LT 4………………………………………………………………………64 Facies L 1………………………………………………………………………..67 Facies S 1………………………………………………………………………..68 Facies S 2………………………………………………………………………..71 Facies LF 1………………………………………………………………………72 Facies T 1………………………………………………………………………..73 Facies T 2………………………………………………………………………..75 Facies LS 1………………………………………………………………………77 Facies LS 2………………………………………………………………………78 Facies LS 3………………………………………………………………………79 Facies M 1……………………………………………………………………….81 CHAPTER 4. PARTICLE SHAPE ANALYSIS……………………………………..82 INTRODUCTION………………………………………………………………………82 METHODS………………………………………………………………………………84 ANALYSIS AND RESULTS.…….…………………………………………………….86 vii DISCUSSION……………………………………………………………………………92 CONCLUSIONS………………………………………………………………………...97 CHAPTER 5. DISCUSSION AND MODEL………………………………………...101 INTRODUCTION……………………………………………………………………...101 MODEL BACKGROUND……………………………………………………………..101 ERUPTIVE AND DEPOSITIONAL MODEL………………………………………...109 Pre-Eruption…………………………………………………...………………..109 Eruption…………………………………………………………………………109 Post-Eruption…………………………………………………………………...112 CONCLUSIONS……………………………………………………………………….114 CHAPTER 6. CONCLUSIONS……………………………………………………...119 REFERENCES CITED……………………………………………………………….122 APPENDICES…………………………………………………………………………144 APPENDIX A: METHODS FOR NIH IMAGE………………………………………144 APPENDIX B: PARTICLE SHAPE ANALYSIS……………...CD-ROM in back pocket viii LIST OF TABLES Table 4.1. Number of analyzed particles that are phreatomagmatic or magmatic for each sample analyzed………………………………………………………………………….96 ix LIST OF FIGURES 1.1: Distribution of middle to late Cenozoic volcanic centers in the southwestern United States………………………………………………………………………………………4 1.2: Map of the Hopi Buttes volcanic field…………………………………...…………10 1.3: Phreatomagmatic landforms and geohydrological environments…………………..13 1.4: Maar deposits and underlying diatreme ………………………………….………...16 1.5: Schematic illustration showing a four-stage fuel-coolant interaction .…………….21 2.1: Field photo of marl deposits………………………………………………………..33 2.2: Field photos of crater-lake deposits………………………………………………...34 2.3: Field photos of Tt…………………………………………………………………...36 2.4: Photomicrographs of Tt…………………………………………………………….36 2.5: Field photo of Ttb…………………………………………………………………..37 2.6: Photomicrograph of Ttb……………………………………………………………37 2.7: Photomicrograph of lava Tla………...……………………………………………..38 2.8: Field photo of lava flows Tla and Tlb………………………………………………39 2.9: Photomicrograph of lava flow Tlc………………………………………………….40 2.10: Field photo of lava flow Tlf……………………………………………………….41 2.11: Field photo of Tlu……………………………………………………………….....42 2.12: Field photo of lava flow Tl2……………………………………………………….43 2.13: Photomicrographs of Tl2…………………………………………………………..44