Collaborative Research: CO2 Springs and Travertines of the Southwestern US: Hydrologic Pathways Linking Tectonism to Water Quality

本项目研究了一个新的假设，即美国西部第四纪石灰华和富含二氧化碳的泉水是构造活动（岩浆活动和地震活动）和水文相互作用的结果。前人的研究表明，美国西部钙华沉积冷泉和热液泉的3He/4He比值表明地幔出气，因此是地幔输入的地表表现。深层来源的流体包括高盐含量和有害的微量元素，如砷和铀，并可能自然混合到科罗拉多高原和里约热内卢大裂谷的含水层系统中。对活泉的水和气的地球化学观察，结合地下水模拟，将有助于了解深源和浅源水文输入之间的联系。我们将研究科罗拉多高原和周围构造省的水和气体；1)评价可能对应地幔输入非均质性和接近年轻玄武岩火山作用的内生水文端元；2)通过水文模拟，量化深源和浅源地下水的混合参数；3)开展第四纪断裂、钙华、钙华沉积泉、CO2场等新构造研究，建立构造与水质的联系。我们使用天然地球化学示踪剂（水中的主要和微量元素包括Sr、Cl/Br、As以及C、H和O的稳定同位素）结合气体化学（3He/4He、CO2、% He、N2/He、N2/CO2、CO2/3He）。研究的空间尺度从局部到区域；时间尺度范围从现代到新近纪晚期钙华矿床中CO2放气的地质记录。该项目包括研究生和本科生的教育和推广工作，研究和教学的整合，通过大峡谷时间之路项目进行的非正式公共教育，以及包括印第安人在内的少数民族的参与。我们正在与国家公园管理局和各个美洲土著部落（华拉派人、哈瓦苏派人和纳瓦霍人）密切合作，他们的水直接受到深层污染物的影响。

This project investigates the novel hypothesis that the Quaternary travertines and CO2-rich springs of the western US are a consequence of the interplay between tectonic activity (magmatism and seismicity) and hydrology. Previous work has shown that travertine-depositing cool springs and hydrothermal springs of the western U.S. have 3He/4He ratios indicative of mantle out-gassing and hence are surface manifestations of mantle inputs. Deeply-sourced fluids include high salt contents and deleterious trace elements such as arsenic and uranium, and may naturally mix into aquifer systems on the Colorado Plateau and the Rio Grande Rift. Observation of the geochemistry of water and gas from active springs, combined with groundwater modeling, will assist in understanding the connections between deep-sourced and shallow-sourced hydrologic inputs. We will examine water and gases in the Colorado Plateau and surrounding tectonic provinces to; 1) evaluate endogenic hydrologic end members that may correspond to heterogeneity in mantle inputs and proximity to young basaltic volcanism; 2) quantify mixing parameters between deeply-sourced and shallow-sourced groundwaters via hydrologic modeling; 3) conduct neotectonic studies on Quaternary faults, travertines, travertine-depositing springs, and CO2 fields to establish the link between tectonism and water quality. We are using natural geochemical tracers (major and trace elements in water including Sr, Cl/Br, As, and stable isotopes of C, H and O) integrated with gas chemistry (3He/4He, CO2, % He, N2/He, N2/CO2, CO2/3He). The spatial scale of the proposed study is from local to regional; the temporal scale ranges from modern to the late Neogene geologic record of CO2 outgassing encoded in travertine deposits. This project includes education and outreach effort at the graduate and undergraduate levels, an integration of research and teaching, informal public education through the Trail of Time project at Grand Canyon, and involvement of minority populations, including Native American. We are working closely with the National Park Service and with various Native American tribes (Hualapai, Havasupai, and Navajo) whose waters are directly impacted by deeply sourced contaminants.