Structural Interpretation of Geology Along a 100 km West-to-East Section of East-Central Idaho

Document Type

Student Presentation

Presentation Date

April 2017

Faculty Sponsor

Walter Snyder


The geology along a 100 km west-to-east section of east-central Idaho reflects Jurassic-Eocene (~150-60 m.y. ago) folding and faulting within the Sevier hinterland. Along this transect, Sevier deformation can be characterized using a thick-skinned inversion tectonic model, where thrust and reverse faults are controlled by older basement normal faults, rather than a distant push, as in thin-skinned deformation farther east. Large-scale folds may have been governed by the buttress effect of a series of subdued horst-block shoulders that remained relatively elevated or were elevated by reverse reactivation of pre-Sevier age normal faults. Shortening along section is reflected by megascopic fault-propagation folds with multi-kilometer amplitudes and wavelengths. Restoration of this section shows 10-15% shortening, considerably less than previous estimates that invoke a thin-skinned model. Restoration using a thick-skinned reactivated fault model does not require the sedimentary cover to be detached from an undeformed basement below. Overturned meter to decameter-scale folds and intraformational thrust faults display flexural-slip within the multi-kilometric scale folds. Smaller-scale structural features can be misinterpreted as indicators of “regional” or “orogen-scale” events. Observations at various scales must utilize different conceptual models in describing the nature, evolution, and deformation of the Cordilleran hinterland.

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