University of Nevada Reno J Determination of Timing of Recharge for Geothermal Fluids in The Great Basin Using Environmental Isotopes and Paleoclimate Indicators A thesis submitted in partial fulfillment of the requirements for the degree of Master of Science, in geology by Paul K. Buchanan 1" April, 1990 i MINES LIBRARY Tti GS Li a (ths The thesis of Paul K. Buchanan is approved by University of Nevada Reno April, 1990 11 ACKNOWLEGEMENTS This study was made possible by grant DE-FG07-88ID12784 from the United States Department of Energy, Geothermal Technology Division, administered by the Idaho Operations Office, Idaho Falls, Idaho. Additional financial assistance from the Nevada Section of the Geothermal Resources Council aided in the completion of this thesis. My thanks go to the Nevada geothermal power industry for allowing fluid sampling of deep powerplant production wells. Specifically, Chevron Resources, Oxbow Geothermal, Ormat Energy Systems, Geothermal Food Processors, Tad's Enterprises, Thermochem Inc., Elko Heat Co. and Elko School District are thanked. Thanks also to Dr. Robert Fournier of the United States Geological Survey for providing data on the Coso geothermal system. Michelle Stickles is to be commended for suffering through the proof reading of the initial drafts of this report. Thanks to my advisor, Jim Carr, and my committee members, Mel Hibbard and Gary Haynes, for taking on this project and putting up with my inconsistent scheduling and "last minute" rush. Special thanks to my cohorts at the Division of Earth Sciences and Mackay School of Mines for their cynical attitudes that helped keep it all in perspec- tive, through both the good and the bad times. Lastly, I must thank Tom Flynn of the Division of Earth Sciences, University of Nevada Las Vegas, for securing the DOE grant and allowing me to be a part of the project. Without his help, I'd likely be making change at Harrah's right now. In spite of the numerous citations above, the author accepts full responsibility for the contents that follow. Ill ABSTRACT Early theories concerning geothermal system recharge in the Great Basin assumed the fluid source was recent precipi- tation. Environmental isotopes and paleoclimatic indicators suggest a more plausible paleorecharge scheme. Polar region isotopic studies demonstrate that a deple- tion in stable light-isotopes of precipitation existed dur- ing the late Pleistocene due to the colder, wetter climate. Isotopic analysis of calcite veins and packrat midden mega- fossils confirm the depletion event occurred in the Great Basin. In this study, non-thermal springs represent local, recent precipitation. Thermal waters are generally more isotopically depleted than non-thermal waters, and represent Pleistocene precipitation. Isolated areas where thermal water is more isotopically enriched than non-thermal water correspond to the location of major Pleistocene lakes, suggesting isotopically enriched lake water contributed to recharge. Carbon age dates and isotopic data from Great Basin thermal waters correlate with the polar paleoclimatic studies. Recharge occurred along range-bounding faults. IV TABLE OF CONTENTS ACKNOWLEDGEMENTS........................................ iii ABSTRACT................................................. iv LIST OF FIGURES........................................ vii LIST OF TABLES...................................... ix CHAPTER 1 . INTRODUCTION.............................. 1 CHAPTER 2. PHYSICAL SETTING........................... 5 2.1 GEOGRAPHY........................................ 5 2.2 GEOLOGY.......................................... 7 2.3 THERMAL CHARACTERISTICS AND GEOTHERMAL RESOURCES . 9 2.3.1 Thermal Characteristics 2.3.2 Geothermal Resources CHAPTER 3. THEORY OF ENVIRONMENTAL ISOTOPES............ 16 3.1 STABLE LIGHT ISOTOPES............................... 17 3.1.1 Hydrogen 3.1.2 Oxygen 3.1.3 Carbon 3.2 ISOTOPE FRACTIONATION PROCESSES.....................22 3.2.1 Isotope Exchange 3.2.2 Other Fractionation Processes 3.3 UNSTABLE LIGHT ISOTOPES AND AGE DATING ........... 31 3.3.1 Tritium 3.3.2 Carbon 3.4 CORRECTION OF CARBON-AGE DATES .................. 35 3.4.1 Atmospheric Correction 3.4.2 Soil and Rock Correction CHAPTER 4. DATA SET COMPILATION. : ................ 42 4.1 LITERATURE SEARCH ............................... 42 4.1.1 Water Samples 4.1.2 Carbon Age Date Samples 4.1.3 Paleoclimatic Data 4.2 FIELD SAMPLING PROGRAM .......................... 45 CHAPTER 5. LABORATORY METHODS........................ 49 5.1 HYDROGEN AND OXYGEN STABLE LIGHT ISOTOPES............49 5.2 WATER CHEMISTRY................................. 5 0 5.3 TRITIUM ANALYSIS ................................ 50 5.4 CARBON ISOTOPES..................................... 51 5.4.1 Water Samples 5.4.2 Carbonate Scale 5.4.3 Analytical Method 5.5 PACKRAT MIDDENS..................................... 53 5.5.1 Hydrogen and Oxygen Isotopes 5.5.2 Carbon-Age Determination V CHAPTER 6. PLEISTOCENE PALEOCLIMATE DATA ............ 55 6.1 GLOBAL ISOTOPIC DEPLETION EVENTS ................. 55 6.1.1 Greenland, Arctic Evidence 6.1.2 Sub-Polar Indian Ocean, Antartic Evidence 6.1.3 Devils Hole, Amargosa Desert, Great Basin 6.2 PACKRAT MIDDENS..................................... 59 6.2.1 Initial Midden Studies 6.2.2 Isotopic Analysis of Midden Macrofossils 6.3 PLEISTOCENE LAKES................................... 67 CHAPTER 7. WATER ANALYSES............................ 71 7.1 COMPUTER CONTOURING OF STABLE LIGHT-ISOTOPE DATA . 71 7.1.1 Undifferentiated Set 7.1.2 Non-Thermal Springs and Precipitation 7.1.3 Thermal Waters 7.1.4 Non-Thermal vs. Thermal Fluids: Isotopic Differences 7.2 GROUNDWATER AGE DATING USING RADIOACTIVE ISOTOPES. 87 7.2.1 Tritium 7.2.2 Carbon-14 CHAPTER 8. DISCUSSION: EFFECT OF PLEISTOCENE LAKES, AND RECHARGE SCHEMES.........................92 8.1 EFFECT OF PLEISTOCENE LAKES.........................92 8.2 RECHARGE SCHEMES ................................ 97 CHAPTER 9. SUMMARY....................................104 9.1 CONCLUSIONS........................................ 104 9.2 RECOMMENDATIONS................................... 105 REFERENCES CITED ..................................... 106 APPENDIX A CURRENT STUDY - STABLE LIGHT ISOTOPE AND GEOCHEMICAL ANALYSES....................116 APPENDIX B LITERATURE SEARCH - STABLE LIGHT ISOTOPES . 119 APPENDIX C CARBON AGE ANALYSES ....................... 151 APPENDIX D PALEOCLIMATE D A T A ......................... 156 VI LIST OF FIGURES Figure 2.1 Location map.............................. 6 Figure 2.2 Basin and Range structural models ........ 10 Figure 2.3 Late Cenozoic extensional faults............ 11 Figure 3.1 Relative isotopic depletion scale ........ 20 Figure 3.2 Temperature vs. Fractionation factor . 24 Figure 3.3 Temperature dependence of isotopic composition of precipitation . 26 Figure 3.4 Rayleigh distillation .................... 27 Figure 3.5 Diagrammatic example of storm rain-out. 29 Figure 3.6 Carbon isotopes in the hydrologic cycle . 34 Figure 3.7 The "Suess effect", recent isotopic depletion of atmospheric carbon. 37 Figure 3.8 Carbon isotope content of several types of material ................ 40 Figure 4.1 Fluid sample locations, this study.......... 48 Figure 4.2 Packrat midden sample locations .......... 48 Figure 6.1 Comparison of 1 80 vs. stratigraphic age from Greenland and Sub-Polar Indian Ocean . 58 Figure 6.2 Comparison of ^ 80 vs. U/TH age from Devils Hole and Sub-Polar Indian Ocean. 58 Figure 6.3 Deuterium vs. radiocarbon age Snake Range packrat middens .............. 62 Figure 6.4 Deuterium vs. radiocarbon age this study, all midden samples............ 65 Figure 6.5 Deuterium vs. radiocarbon age this study, Painted Hills midden.......... 65 Figure 6.6 Deuterium vs. radiocarbon age, Snake Range and Painted Hills middens . 66 Figure 6.7 Maximum extent of Pleistocene Lake Lahontan and Lake Bonneville........ 68 Figure 6.8 Lake level chronology of Pleistocene Lake Lahontan and Lake Bonneville........ 7 0 Figure 7.1 Contoured deuterium, all fluid samples. 73 Figure 7.2 Contoured oxygen-18, all fluid samples. 73 Figure 7.3 Deuterium vs. 180, non-thermal springs. 75 Figure 7.4 Contoured deuterium, non-thermal springs. 77 Figure 7.5 Stormtracks which bring precipitation to the Great Basin.......... 77 Figure 7.6 Contoured oxygen-18, non-thermal springs. 78 Vll LIST OF FIGURES, Continued Figure 7.7 Contoured deuterium, thermal springs. 79 Figure 7.8 Contoured deuterium, thermal wells. 79 Figure 7.9 Contoured oxygen-18, thermal springs. 81 Figure 7.10 Contoured oxygen-18, thermal wells. 81 Figure 7.11 Deuterium vs. ^ 0 , Beowawe, Nevada, area. 82 Figure 7.12 Deuterium vs. 1^0 , Caliente, Nevada, area 82 Figure 7.13 Contoured deuterium, thermal springs minus non-thermal springs 84 Figure 7.14 Contoured deuterium, thermal wells minus non-thermal springs . 84 Figure 7.15 Contoured oxygen-18, thermal springs minus non-thermal springs 86 Figure 7.16 Deuterium vs. 1^0, demonstrating worldwide occurence of oxygen shift . 86 Figure 7.17 Location of radiocarbon age analyses. 90 Figure 7.18 Deuterium vs. radiocarbon age, northern Nevada thermal waters.......... 91 Figure 8.1 Location of Painted Hills and Snake Range midden studies in relation to Pleistocene Lake Lahontan and Lake Bonneville ........ 93 Figure 8.2 Deuterium vs. radiocarbon age for Painted Hills middens, compared to Lake lahontan level chronology............ 94 Figure 8.3 Deuterium vs. radiocarbon age for Snake Range middens, compared to Lake Bonneville level chronology.......... 94 Figure