Date of Graduation

Spring 2018


Master of Science in Geospatial Sciences


Geography, Geology, and Planning

Committee Chair

Matthew McKay


Blue Mountains Province, western Idaho shear zone, Salmon River suture zone, Purgatory Saddle quadrangle, Oxbow-Cuprum shear zone, gravity analysis

Subject Categories

Geology | Geophysics and Seismology | Tectonics and Structure


Western Idaho (USA) contains deformation associated with the Mesozoic accretion of volcanic island arc terranes of the Blue Mountains Province to Laurentia. The near vertical boundary between the accretionary orogeny and Precambrian North America is represented by the transpressional western Idaho shear zone, which lies east of metamorphic rocks in the Salmon River suture zone. The Blue Mountains Province in western Idaho contains four accreted crustal blocks: the Wallowa, Olds Ferry, Baker, and Izee terranes. The purpose of this study is to understand the structural relationship of the pre-accretionary, syn-accretionary and post-accretionary tectonic features along the accreted terrane boundary in western Idaho. High resolution 7.5-minute geologic mapping of the Purgatory Saddle quadrangle reveals tectonic relationships of plutonism and deformation in the pre-accretionary, Oxbow-Cuprum shear zone in the Wallowa terrane. Gravity and magnetic analysis of the boundary between accretionary island arcs and Precambrian North America reveals subsurface relationship of the western Idaho shear zone and the Salmon River suture zone. We present 2.5-D crustal scale gravity models across the Salmon River suture zone and the western Idaho shear zone to constrain the subsurface geometry of the accretionary boundary, and propose a newer extent of the Salmon River suture zone to the south and a western extent of the western Idaho shear zone.


© Sourav Krishna Nandi

Geologic_Map_Purgatory_Saddle_Quad.pdf (8750 kB)
Geologic map and cross sections

Open Access