Date of Award
Master of Science
Geological and Environmental Sciences
Dr. Christopher J. Schmidt
Dr. Gerry Clarkson
Dr. W. Thomas Straw
Masters Thesis-Open Access
Gravity modeling of west-dipping, Laramide mountain flank thrusts which involve Archean metamorphic rocks in the western Tobacco Root and northern Madison Ranges supports the idea that these thrusts are gently dipping.
The thrusts provided a favorable location for normal faulting during Neogene extension. The Neogene faults on the eastern portions of the Madison and Jefferson Basins are interpreted to be listric, and merge with the Laramide thrusts. Basin development occurred along a series of such faults, which dropped hanging wall blocks of the thrust sheets to progressively greater depths. The maximum depth of the Madison basin, near Ennis, was found to be about sea-level.
The depth of the Jefferson Basin is found to change from sea-level near Dry Boulder Canyon, to -3000 feet near Hellroaring Canyon. This change is interpreted to be the result of a northwest-trending fault (northeast side downthrown) crossing the basin.
Wigger, Stephen Thomas, "A Gravity Investigation of Mountain Flank Thrusting and Normal Faulting, Madison and Tobacco Root Ranges, Montana" (1985). Master's Theses. 1462.