Abstract

Structural studies in Upper Cretaceous and Eocene sedimentary rocks in the High Plateaus of southwestern Utah attempted to establish the cause of layer-parallel shortening expressed in a regional-scale arcuate pattern of thin-skinned thrusts and related structures. The thrusts sole into Jurassic evaporites of the Carmel Formation. Tectonic transport direction verges radially from 125° to 215°. Stress analysis reveals a fan-like pattern of the principal compressional stress sweeping southeastward to south-south-westward through 90° along an arc extending 35 km across the Paunsaugunt Plateau. Regional compressional structures of Sevier and Laramide origin are older than the thin-skinned deformation, and regional extensional structures of Basin and Range origin are younger. The thrusting postdates deposition of the Claron Formation (Eocene) and probably took place in the interval 30 Ma to 20 Ma, that is, coeval with the formation of the Marysvale volcanic center located 40 to 60 km northwest of the thrust belt. The forces that created the thrusts could have formed through a combination of processes related to the dynamics of formation of the Marysvale volcanic center, including gravity gliding and/or compressional push related to the emplacement of batholithic intrusions, and gravitational spreading and/or end-loading related to vertical loading of the column and the underlying evaporite décollement by the weight of the thick Marysvale volcanic pile.

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