DETAILED GRAVITY ANALYSIS OF GEOTHERMAL FEATURES IN WESTERN YELLOWSTONE NATIONAL PARK

The Yellowstone volcanic complex (YVC) of northwestern Wyoming is part of a larger magmatic system that extends southwest through the Snake River Plain in Idaho. The YVC has long been associated with a stationary plume source, however, recent seismic and magnetotelluric studies have been interpreted to support both plume and nonplume sources. Seismic tomography models indicate that the slowest velocities are directly below the caldera system and gravity studies have confirmed this result with the YVC being associated with a high amplitude gravity minimum. The highest amplutide gravity minima occur in the northeastern portion of the caldera under the Sour Creek Dome and are interpreted to be caused by partially melted siliceous material in the lower crust. Despite all the regional geophysical interpretations, there have been few detailed gravity investigations of the structures within the geothermal features in the YVC. In this study, I collected 170 gravity stations spaced between 300 and 400 meters between the Lone Star Geyser region and the Lower Geyser Basin. These station collected using differential GPS and processed using terrain corrections were merged with existing data to produce a complete Bouguer gravity anomaly map. This map indicates that the Mallard Dome Lake Dome, the Lone Star Geyser region and the northern section of the Lower Geyser Baisn are associated with gravity minima probably associated with deep hydrothermal alteration. The Upper Geyser Basin is on the edge of a gravity maximum suggests that the deeper alteration of the rhyolitc rocks is not as intense but additional data are needed to confirm this observation. Additional analyse will include the construction of residual and derivative maps in order to better interpret the gravity data.