Abstract

Low-angle faults that place younger strata on older are the distinctive structural feature of the hinterland of the Sevier orogenic belt in Nevada. Although shown on many maps as Mesozoic thrust faults, these low-angle faults may in many places be extension, denudation, and gravitational gliding features of Tertiary age. The complexity of later Tertiary deformation caused by crustal extension in the hinterland has not been sufficiently emphasized.

Several contrasting interpretations of the relation between hinterland and Sevier belt structures exist. Whitebread, Hose, Roberts, and Crittenden advocate gravitational gliding models that differ in detail, but in general they correlate extension in the hinterland with thrusting toward the foreland during the Cretaceous. Misch, Nelson, Fritz, Miller, and Woodward assign a Mesozoic age to the low-angle faults which they relate to a regional décollement. The frontal breakout of this deacute;collement is proposed by them to be west of, and older than, the thrust faults of the Sevier belt or perhaps equivalent in age to them. Other geologists (Armstrong, Burchfiel, Davis, and Fleck) argue for a compressional origin for the Sevier belt that involves considerable crustal shortening. To them the low-angle hinterland faults are unrelated to Sevier belt thrusting. Geometric and chronologic problems are created by the first two interpretations, making the third interpretation most attractive.

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