Uplifts, the Primary Structures of Deformation in the Shelf and Miogeosyncline of the Western United States: ABSTRACT

Abstract

The large asymmetrical and elongate domes that constitute the basic structure of the ranges of the shelf province of Montana, Wyoming, Colorado, New Mexico, and the Colorado Plateau of Utah and Arizona are depicted as primary structures with the flanking thrusts as secondary gravity slide phenomena. End_Page 338------------------------------ The miogeosyncline of western Utah and eastern Nevada is analyzed for its pre-Basin and Range and pre-volcanic structures, and an outcrop pattern arrived at that shows uplifts similar to those of the shelf. A number of thrusts are believed to be gravity slide structures on the flanks of the uplifts, and most of the folds and associated thrusts are squeeze structures between the uplifts. These latter compose synclinoria with thick Pennsylvanian and Permian sections. The uplifts, including those of the Ancestral Rockies as well as some in the miogeosyncline, have had a history beginning with the Pennsylvanian. Vigorous uplifting reached a climax in the Late Cretaceous and Early Tertiary. All of the uplifts owe their existence to magmatism, in which basalt from the mantle has risen to the interface between the granitic and basaltic layers to form megalenses or blisters. End_of_Article - Last_Page 339------------