--> Tectonic setting and resulting characteristics of the Paisley Geothermal System, Paisley, Oregon

AAPG Pacific Section and Rocky Mountain Section Joint Meeting

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Tectonic setting and resulting characteristics of the Paisley Geothermal System, Paisley, Oregon

Abstract

Geothermal resources in the western United States are characterized by two end member types- magmatic and amagmatic (i.e., the Basin and Range type). Basin and Range systems are almost always associated with areas of high regional heat flow, thermal waters containing low concentrations of magmatically derived chemical species, and are highly dependent on the local and regional structural framework. Though these conditions exist in southeast Oregon, few detailed studies of the geothermal resources in this area have been conducted. Paisley lies at the intersection of many geologic provinces. The northwest margin of the Basin and Range is typically drawn near Paisley along with the southern boundary of the High Lava Plains and the eastern boundary of the High Cascades. Given the proximity to both structurally and volcanically active terranes, it is feasible that the Paisley Geothermal System could be of either type, or some hybrid of the two. However, based on the results of this study, the Paisley Geothermal System has been identified as the Basin and Range type. Geographically extensive high heat flow values averaging 150 mW/m2 provide evidence of a regional heat flow high. Low concentrations of SO4, As, B and high values of HCO3 and Na suggest that the thermal fluids are not influenced by magmatic activity. This is further evidenced by stable isotope values of the thermal fluids, which show they are most likely of meteoric affinity. The pathways for fluid flow has been determined to be within a structural transfer zone, where left-lateral shear transfers strain between the Paisley Hills and Winter Ridge Faults.