Abstract: Geothermal Systems of Corwin Springs-Gardiner Area, Montana--Structural and Lithologic Controls

Eric Mitchell Struhsacker

Hot-springs activity has persisted in the Corwin Springs-Gardiner, Montana, area since the Pleistocene. The only active hot springs, La Duke and Bear Creek, emerge at opposite ends of a 2-sq-mi (5 sq km) Pleistocene travertine deposit.

The hot springs and travertine lie along the northwest-trending Gardiner fault, a Laramide high-angle, reverse, imbricate fault zone which bounds the Bear-tooth crystalline rock uplift on the southwest. The post-Laramide Reese Creek and Mammoth faults are normal faults that form graben and extend from the Yellow-stone Park upland northward into the hanging wall of the Gardiner fault. The local thermal features are on or between the intersections of these faults with the Gardiner fault zone.

More than 10,000 ft (3,000 m) of Paleozoic and Mesozoic sedimentary rock is preserved within the graben in the footwall of the Gardiner fault. From a structural high within Yellowstone Park, the sedimentary units dip gently into the Gardiner fault zone, where they are dragged up and overturned locally to form an asymmetric syncline striking northwest. These structural relations suggest that meteoric waters flow down permeable sedimentary units within the graben from the Yellowstone upland to great depth under the Gardiner fault zone, thereby forming a common reservoir for the hot-spring systems. The cavernous Mississippian Madison Limestone, lying near a depth of 10,000 ft (3,000 m) under the Gardiner fault zone, may be the principal aquifer and produce the high calcium content of the active hot springs.

Waters are heated at depth by conduction from rocks whose temperatures depend on the geothermal gradient. They then ascend through fractures to the surface. A normal thermal gradient for western Montana causes base temperatures near 100°C at this depth. However, the proximity of a shallow magma body beneath the Yellowstone Plateau on the south may accentuate the normal regional thermal gradient and produce higher base temperatures in the reservoirs.

AAPG Search and Discovery Article #90968©1977 AAPG-SEPM Annual Convention and Exhibition, Washington, DC