Abstract

The Cordilleran orogenic belt of North America was formed during an orogeny which occurred mainly in Cretaceous and Paleocene time. The belt is marked by a zone of strong folding and thrust faulting that extends from Alaska to Guatemala. However, between southern Nevada and northeastern Chihuahua, the belt is so obscured that some geologists doubt its continuity. A recent study of part of the Nevada-Chihuahua interval provides evidence that the belt is continuous, without major interruption; the complications are the result of pre-orogenic and post-orogenic tectonic events. With due regard for these complicating factors, a structure section through southeastern Arizona and southwestern New Mexico closely resembles sections through southwestern Canada, regions near Salt Lake City and Las Vegas in the United States, and northern Mexico. In each region, supracrustal rocks were tectonically transported east-northeastward a distance probably more than 100 km. The style of deformation suggests a near-surface environment, probably mainly controlled by décollement between a prism of miogeosynclinal rocks and crystalline basement rocks. Those features which vary between the regions reflect differences in tectonic position within the belt (for example, closer to foreland or hinterland, or depth of exposure), in anisotropy of preorogenic rocks (variations in older structural features), or in subsequent geologic history.

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