SUBSURFACE CHARACTERIZATION OF THERMAL SPRINGS IN CASCADE RANGE AND OLYMPIC MOUNTAINS, WASHINGTON USING MULTIPLE MINERAL EQUILIBRIA GEOTHERMOMETRY
Most estimated temperatures for Cascade waters (53-153 oC) are hotter than Olympic waters (53-103 oC). These MME estimates generally fall within the ranges projected by some select conventional geothermometers (Cristobalite, Chalcedony, Quartz, Na/K, and Na-K-Ca). The average difference between reservoir and discharge temperatures is greater in the Cascade springs (x̅difference: 53 oC vs 27 oC). Furthermore, the Cascade waters show more evidence of chemical evolution since ascent, as Carson (groundwater dilution=24%), Bonneville (CO2 degassing=23%), and Ohanapecosh (CO2 degassing=2%) were corrected for disequilibria. Conversely, all five Olympic springs are apparently still in equilibrium with their last reservoir.
The geothermal fluids feeding the Cascade springs may be undertaking an indirect or variable path to the surface, as reflected by a greater temperature difference between surface and reservoir and evidence of physical changes and a structurally complex volcanic arc setting. On the other hand, the fully equilibrated Olympic waters appear to have been cooled to a lesser extent during upflow and cycled through thrust-imbricated turbidites, so there may be a more direct connection between the reservoir and the springs.