University of New Mexico UNM Digital Repository Earth and Planetary Sciences ETDs Electronic Theses and Dissertations Fall 9-21-2016 Birth and evolution of the Rio Grande fluvial system in the last 8 Ma:Progressive downward integration and interplay between tectonics, volcanism, climate, and river evolution Marisa N. Repasch Follow this and additional works at: https://digitalrepository.unm.edu/eps_etds Part of the Geology Commons, Geomorphology Commons, Hydrology Commons, Other Earth Sciences Commons, Sedimentology Commons, Tectonics and Structure Commons, and the Volcanology Commons Recommended Citation Repasch, Marisa N.. "Birth and evolution of the Rio Grande fluvial system in the last 8 Ma:Progressive downward integration and interplay between tectonics, volcanism, climate, and river evolution." (2016). https://digitalrepository.unm.edu/eps_etds/139 This Thesis is brought to you for free and open access by the Electronic Theses and Dissertations at UNM Digital Repository. It has been accepted for inclusion in Earth and Planetary Sciences ETDs by an authorized administrator of UNM Digital Repository. For more information, please contact [email protected]. Marisa Repasch Candidate Earth and Planetary Sciences Department This thesis is approved, and it is acceptable in quality and form for publication: Approved by the Thesis Committee: Karl Karlstrom Laura Crossey Matt Heizler i BIRTH AND EVOLUTION OF THE RIO GRANDE FLUVIAL SYSTEM IN THE LAST 8 MA: PROGRESSIVE DOWNWARD INTEGRATION AND INTERPLAY BETWEEN TECTONICS, VOLCANISM, CLIMATE, AND RIVER EVOLUTION BY MARISA REPASCH B.S. EARTH AND ENVIRONMENTAL SCIENCES LEHIGH UNIVERSITY 2014 M.S. THESIS Submitted in partial fulfillment of the Requirements for the Degree of Master of Science Earth and Planetary Sciences The University of New Mexico Albuquerque, New Mexico December, 2016 ii ACKNOWLEDGEMENTS First and foremost, I acknowledge my advisor, Karl Karlstrom, for all of the guidance, time, and energy he invested in my research, professional development, and personal well-being. As a result of his mentorship I have gained broad and diverse geological skillsets, improved my aptitude for answering geological problems, and developed the confidence I need to succeed in academia. I need to thank Matt Heizler and Lisa Peters at the New Mexico Geochronology Research Laboratory in Socorro, NM. Acquisition of my 40Ar/39Ar data greatly contributed to our overall understanding of the Taos Plateau, which would have been impossible without their hard work and patience in the lab. Next I express gratitude to all of the professors who influenced me academically over the last two years, including Laura Crossey, Grant Meyer, Yemane Asmerom, Joe Galewsky, and Sean Penman. Through their pedagogy I gained valuable skills in geochemistry, geomorphology, numerical modeling, and geospatial analysis. These skills continue to be valuable to me as I continue my academic career in the Earth Sciences. I must also recognize the numerous organizations that provided the funding that made my research possible, including National Science Foundation (NSF) EPSCOR award #IIA-1301346 to Laura Crossey and Karl Karlstrom, the Geological Society of America/ExxonMobil student geoscience grant, the New Mexico Geological Society, and the University of New Mexico Graduate-Professional Student Association. iii BIRTH AND EVOLUTION OF THE RIO GRANDE FLUVIAL SYSTEM IN THE LAST 8 MA: PROGRESSIVE DOWNWARD INTEGRATION AND INTERPLAY BETWEEN TECTONICS, VOLCANISM, CLIMATE, AND RIVER EVOLUTION by Marisa Repasch B.S., Earth and Environmental Sciences, Lehigh University, 2014 M.S., Earth and Planetary Sciences, University of New Mexico, 2016 ABSTRACT The Rio Grande-Rio Chama (RG-RC) fluvial system has evolved dramatically over the last 8 Ma, undergoing channel migrations, drainage capture and integration events, volcanic damming, and carving and refilling of paleocanyons. Volcanism concurrent with the development of the river system provides a unique opportunity to apply multiple geochronometers to the study of its incision and drainage evolution. This paper reports 19 new 40Ar/39Ar basalt ages and 19 detrital mineral samples (zircon and sanidine) collected from RG-RC alluvium overlain by dated basalt flows in the context of a compilation of published 40Ar/39Ar basalt ages. The “run-out” geometry of 4.8 Ma basalts at Black Mesa suggests that the course of the northern Rio Grande connecting the San Luis to Española basins was established by then. Detrital zircon age spectra for ancestral Rio Grande alluvium underlying these basalt flows contain 10-12% of 37-27 Ma grains suggesting that the ~5 Ma Rio Grande had its headwaters in the San Juan Mountains. The 5-3 Ma accumulation of basalt flows on the Taos Plateau was accompanied by inset relationships downstream (near Black Mesa) documenting the iv existence of a developing 5-2.5 Ma Rio Grande valley that provided downstream discharge. Coincident timing and pre-volcanic knickpoints suggest that surface uplift associated with the construction of the Taos Plateau volcanic field drove downward integration to the Palomas basin by 4.5 Ma. Changes in ancestral Rio Grande sediment provenance from 2.6 Ma to 1.6 Ma document a northward shift of the RG-RC confluence and indicate that surface uplift of the Jemez Mountains (Valles Caldera) likely drove further downstream integration. The Taos Plateau volcanic field reduced through-flowing surface drainage from the San Juan Mountains relative to the Sangre de Cristo Mountains until the ~0.69-0.44 Ma spillover of Lake Alamosa, but we view this event as a re- integration, not initial integration, of upper Rio Grande drainage. Progressive downward integration of rift-aligned basins from 8 to 1 Ma was likely facilitated by waning rift extension that allowed aggradation to exceed subsidence. Downward integration events crudely mimic climate change “events” at 6 Ma (onset of the southwestern monsoon) and 2.5 Ma (global change toward glacial-interglacial climate). Magmatic influences include the 6-2.5 Ma building of the Taos Plateau volcanic field, Jemez Mountain caldera eruptions at 1.6 and 1.25 Ma, along with continued magmatism that developed constructional topography and Jemez lineament volcanism that may have been associated with mantle-driven epeirogenic uplift across northern New Mexico. Integration of the RG-RC system to the Gulf of Mexico by 0.8 Ma was facilitated by headwater uplift as well as increased frequency of ~100 ka high-amplitude glacial-interglacial cycles that contributed to higher discharge and bedrock incision rates during the Pleistocene. We conclude that magmatic and tectonic drivers dominated over v the last ~8 Ma, but were amplified by climate change events to determine the fluvial evolution of the RG-RC system. vi TABLE OF CONTENTS 1. INTRODUCTION…………………………………………….……………….xiv 2. ANNOTATED SYNTHESIS OF PREVIOUS WORK………………………..4 2.1. Role of Rio Grande rift structure and magmatism in localizing drainage…………………………………………………………….…………4 2.2. Summary of axial facies (trunk rivers) of rift basins ..............................6 2.3. Lava dams and interactions between the river and volcanism .............12 2.4. The “Turnaround” from aggradation to incision ..................................15 2.5. Red River headwaters and spillover of Lake Alamosa hypotheses ......17 2.6. Roles of climate and tectonics ..............................................................20 3. NEW RESEARCH……………………………………………………………...22 3.1. METHODS .............................................................................................22 3.1.1. River profile analysis ............................................................................22 3.1.2. Application of multiple geochronometers ............................................23 3.1.3. 40Ar/39Ar basalt geochronology ............................................................24 3.1.4. U-Pb Detrital Zircon Geochronology ...................................................24 3.1.5. 40Ar/39Ar detrital sanidine geochronology ............................................26 3.2. RESULTS ................................................................................................27 3.2.1. Samples analyzed .................................................................................27 3.2.2. River profile analysis ............................................................................30 3.2.3. 40Ar/39Ar Basalt Ages for the Taos Plateau Volcanic Field .................32 3.2.3.1. Old State Bridge, Colorado .............................................................33 3.2.3.2. La Junta Point ..................................................................................33 3.2.3.3. Dunn Bridge Section .......................................................................34 3.2.3.4. Gorge Bridge Section ......................................................................35 3.2.3.5. Pilar Mesa ........................................................................................36 vii 3.2.3.6. Rinconada ........................................................................................37 3.2.3.7. Black Mesa-La Mesita Area ............................................................37 3.2.4. Detrital zircon and sanidine analysis ....................................................38 3.2.4.1. Ancestral Rio Grande-Rio Chama system (5 to 1 Ma) ...................40 3.2.4.2. Late Pleistocene to modern Rio Grande- Rio Chama system (640 to 0 ka)……………………………………………………………….46 3.3. INTERPRETATION…………………………………………………………...51