Date of Graduation

Spring 2017

Degree

Master of Natural and Applied Science in Geography, Geology, and Planning

Department

Geography, Geology, and Planning

Committee Chair

Kiven Mickus

Keywords

Great Falls Tectonic Zone, gravity, magnetics, magnetotellurics, Wyoming craton, paleoproterozoic tectonics

Subject Categories

Mineral Physics | Tectonics and Structure

Abstract

The Great Falls Tectonic Zone (GFTZ) is a northeast trending zone of high angle faults and lineaments extending from northeastern Idaho into Saskatchewan, Canada. The GFTZ is believed to have facilitated the collision between the Archean Wyoming and Hearne cratons. Previous geophysical studies have analyzed seismic refraction data across the boundary between the Paleoproterozoic GFTZ and Archean Wyoming Craton (WC), this indicated the lower crustal layer thickens as it dips beneath the boundary towards the WC. In this study, three 2 dimensional (2D) gravity models that crossed the central region of the GFTZ were produced using constraints from existing geologic and geophysical studies. The construction of a complete Bouguer gravity anomaly map, regional and residual (band-pass filtered) gravity and magnetic maps, as well as the generation of 2D magnetotelluric electrical resistivity profiles greatly aided in the interpretation of areas of interest. Coupled with the newly developed maps, the models provide otherwise unavailable constraints on the extent and geometries of the GFTZ/WC boundary region. Additional geophysical analysis of these features may substantiate the findings and help redefine the subsurface extent of the GFTZ/WC boundary. Low resistivity values in the upper mantle may be related to release water formed during subduction of cratonic material during the Paleoproterozoic.

Copyright

© Travis Lane Fultz

Open Access

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