RESEARCH ARTICLE Pre-Thrusting Stratigraphic Control on the Transition 10.1029/2020TC006429 From a Thin-Skinned to Thick-Skinned Structural Style: Key Points: An Example From the Double-Decker Idaho-Montana • Thin-skinned and thick-skinned thrusts record a progressive Fold-Thrust Belt downward shift in the basal detachment of the Idaho-Montana S. D. Parker1 and D. M. Pearson1 fold-thrust belt • A transition from thin-skinned to 1Department of Geosciences, Idaho State University, Pocatello, ID, USA thick-skinned thrusting occurred as the basal detachment encountered the basement high of the Lemhi arch • Thin-skinned thrusts in the Abstract Continental fold-thrust belts display a variety of structural styles, ranging from thin-skinned overlying cover and thick-skinned thrusts following weak lithologic contacts to thick-skinned thrusts that deform mechanical basement. thrusts below the basement/cover The common practice of splitting fold-thrust belts into thin-skinned and thick-skinned map domains has contact form a double-decker fold- thrust belt not yielded a predictive model of the primary controls on structural style. Within the Mesozoic-Paleogene Idaho-Montana fold-thrust belt (44°N-45°N, 112°W-114°W), we identify crosscutting thin-skinned and thick-skinned thrusts within an otherwise thin-skinned map domain. This transition occurs within a Correspondence to: thin ( 2.5 km) portion of the western Laurentian passive margin, where lower strata pinch out over a S. D. Parker,
[email protected] prominent∼ basement high (Lemhi arch). Early fold-thrust belt shortening of sedimentary cover rocks was accommodated through detachment folding, followed by east-directed, thin-skinned thrusting along Citation: regional-scale faults (Thompson Gulch and Railroad Canyon thrusts).