Integrated Hyperspectral, Geophysical and Geochemical Studies of Yellowstone National Park Hydrothermal Systems Completed

Sources/Usage: Public Domain.

Science Issue and Relevance

Although Yellowstone's hydrothermal systems are well mapped at the surface, their subsurface groundwater flow systems are almost completely unknown since clear images of Yellowstone groundwater resource locations, geometry, salinity and temperature are lacking in the Park. In addition to a legacy of geochemical work on thermal waters, geophysical mapping, and application of remote sensing techniques to characterize surface geology, the USGS put in a series of drill holes in between 1967 and 1969 to obtain detailed physical and chemical data for the shallow (<330 m depth) hydrothermal system. The core extracted from these drill holes is archived in the USGS Core Research Center in Denver, CO. The Yellowstone core is an invaluable resource for non-destructive research activities, and access to this material has been provided for mineral assemblage characterization using hyperspectral techniques. Preliminary results from a 2001 hyperspectral survey of the Norris Geyser Basin indicate that a wide range of hydrothermal alteration minerals were successfully mapped. Despite the amount of data, there is a major knowledge gap between the surface hydrothermal systems and the deeper magnetic system.

Methodology to Address Issue

We are researching the subsurface groundwater flow systems in Yellowstone and the relation of these systems to understanding the regional movement of water in a volcanic center. New geophysical data will be integrated with existing data sets from hyperspectral data from Yellowstone's thermal areas and thermal water geochemistry to help define regionally extensive mineral assemblages, the evolution of fluid types that form these mineral assemblages, and to determine trace metals associated with these mineral assemblages. Yellowstone's thermal basins include different geologic settings, and each geologic setting is expected to have different mineral assemblages and resultant alteration by hydrothermal fluids. Additionally, there is a broad range of pH and temperatures in regional thermal water that can influence alteration mineral assemblages.

These combined data can be used to develop a more complete understanding of the subsurface structure that influences different thermal water compositions, which will allow for a more nuanced understanding of how mineral assemblages in the Yellowstone subsurface were formed. Our overarching objective is to develop a series of basin-specific characterizations in Yellowstone National Park using a combination of hyperspectral, geophysical, and geochemical data. Selected basins will each be the subject of a focused, interdisciplinary effort, prioritized in part by the planned geophysical surveys and existing hyperspectral data. These data sources will be supported with the synthesis of other data coverages, including surface hydrology, LiDAR, and geology.

Hyperspectral Imaging: We plan to construct a three-dimensional synthesis of hydrothermally altered mineral assemblages using existing hyperspectral surveys and data from the Yellowstone drill core. New spectral data for mineral phases are being used to reinterpret data from remote sensing surveys to provide information on surface mineralogy and geology at the meter to kilometer scale. Core data are being evaluated to obtain mineralogical and geochemical data at the scale of centimeters to nanometers.

Sources/Usage: Public Domain.

Sources/Usage: Public Domain.

Sources/Usage: Public Domain.

Mineral identification is performed on the micrometer scale using a combination of scanning electron microscopy (SEM) and electron microprobe. There are two major phases of rare earth element (REE)-bearing minerals that have been identified, the phosphate mineral monazite and carbonate minerals with a range of rare earth element5 concentrations. Both of these minerals phases have associated halide elements chlorine and fluorine. These halide elements are being monitored by USGS Yellowstone Volcano Observatory personnel to evaluate changes in thermal water activity. Thus, using these mineral phases to understand the fluids that deposited them becomes important for evaluating the history of hydrothermal groundwater interacting with the Lava Creek Tuff in Norris Geyser Basin.

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Geophysical Characterization: We are conducting a helicopter electromagnetic and magnetic (HEM) survey in November 2016 in collaboration with scientists from the University of Wyoming and Aarhus University in Denmark. The HEMsurvey will provide the first synoptic subsurface view of Yellowstone's hydrothermal systems, tracking the geophysical signatures of geysers, hot springs, mud pots, steam vents and hydrothermal explosion craters to depths down to hundreds of meters. We hope to distinguish zones of cold fresh water, hot saline water, steam, clay and unaltered rock from one another to understand Yellowstone's myriad hydrothermal systems. The data collected from the November 2016 flight will guide future ground-based geological, hydrological and geophysical studies.

Sources/Usage: Public Domain.

Geochemical Characterization: Yellowstone thermal waters include components of magmatic, or very deep groundwater, and meteoric, or precipitation sources. As groundwater moves through bedrock in the region, the superheated waters dissolve minerals, with the resulting water chemistry reflecting the elements that are in the rocks. The geochemical component of the study seeks to identify geologic sources of some of these elements (e.g., rare earth elements - REE) and to distinguish between magmatic and bedrock sources of mercury and other elements that have forms that can occur in volatile, or gaseous forms. This work is being conducted in collaboration with personnel in the USGS Water Mission Area. The water chemistry will be interpreted along with rock chemistry to better understand the interchange between deep, magmatic waters and shallow groundwater flowpaths.