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The AAPG/Datapages Combined Publications Database
AAPG Bulletin
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The Stewart Peak culmination, located in the northern Salt River Range of the Idaho-Wyoming thrust belt, is an anticlinorium in the hanging wall of the Absaroka thrust fault. The culmination is topographically and structurally higher than areas to the north or south and consists of the oldest rocks exposed in the thrust belt. Rocks from the lower part of the Absaroka thrust sheet, ranging in age from Middle Cambrian to Mississippian, are stacked by an anastomosing network of imbricate thrust faults. Fold geometries include kink, chevron, and open concentric forms which deformed by a flexural-slip mechanism.
Structural culminations are an important and predictable component of most fold-and-thrust belts. Down-plunge projections from culminations into adjacent depressions are often the key to unraveling complex structural relations. Several factors may contribute to the development of a culmination.
Surface geologic mapping, integrated with down-plunge projections and geophysical data, indicate that the Stewart Peak culmination is the result of polyphase uplift and arching of the Absaroka thrust sheet by motion on younger and structurally lower thrust faults,
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namely the Murphy and Firetrail thrusts. These younger faults are interpreted to sole into the overlying Absaroka thrust, forming a subsurface duplex zone which may have considerable oil and gas potential. In addition, magnetic data suggest that the Stewart Peak culmination may be positioned over the northwest continuation of the Moxa arch, an anticlinal flexure of authochthonous basement which formed contemporaneously with thin-skinned thrusting.
The Stewart Peak culmination is compared to structural culminations in the Canadian Rockies and the southern Appalachian orogene of Virginia and Tennessee. Culminations are prospective areas for oil and gas, and traps may be formed in a variety of geometric configurations.
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