Tectonics of Colorado Plateau: ABSTRACT

Abstract

The Colorado Plateau structural province consists of seven principal basins, nine principal uplifts, and several intermediate tectonic divisions such as platforms, slopes, sags, and broad saddles. Long monoclinal flexes between uplifts and basins are the principal lines of deformation in and marginal to the Plateau. The Plateau may be divided roughly into northeastern and southwestern parts which differ considerably as to the magnitude and form of the principal tectonic elements. The northeastern part includes the major basins (Uinta, Piceance, and San Juan), the Paradox fold and fault belt, and uplifts End_Page 789------------------------------ and monoclines that generally face southwesterly. The southwestern part includes the minor basins (Henry, Kaiparowitz, Black Mesa, and Blanding), the broad Mogollon slope, and uplifts and monoclines that generally face eastward. The salt anticlines, piercements, and graben of the Paradox basin are the most special structures of the Plateau. Their folding and piercement began in Permian time, continued intermittently through Triassic and Jurassic time, and culminated in Laramide time. Subsequent collapse may be partly related to Cretaceous loading, partly to Laramide folding, and partly to solution of the salt. In addition to the elongate, tangentially compressed uplifts such as San Rafael, Circle Cliffs, or Zuni, there are several domical uplifts due to the stock and laccolithic intrusions such as the La Sal, Abajo, or Ute centers. These centers fall on three nearly parallel, northwesterly trending lines. The earliest tectonic events that appear to have influenced the present structure occurred during late Paleozoic time. Three northwesterly trending Permo-Pennsylvanian positives developed on and adjoining the Plateau. From northeast to southwest, these are the Front Range, Uncompahgre, and Zuni. All appear to have been asymmetrical toward the southwest where they were immediately adjoined in order by the Colorado, Paradox, and San Juan sags or basins. During Triassic and Jurassic time, local folding occurred in the Paradox fold belt and elsewhere and broad, slight epeirogenic sagging developed in a northwesterly direction between the Uncompahgre and Zuni positives. In late Jurassic time, the southern rim of the Plateau was generally tilted northward. During late Cretaceous time, the P ateau was markedly depressed and slowly tilted northward as it became a part of the Rocky Mountain geosyncline. Despite the fact that the descriptive tectonics of the Plateau are fairly well known, there still remain several problems concerning the cause, nature, and history of deformation and the character, nature, and history of fluid movement. Among these problems are (1) influence of the Precambrian structures on later deformation, (2) Paleozoic and Mesozoic diastrophisms as interpreted from stratigraphy, (3) cause and nature of Laramide movements especially in relation to the formation of the adjoining Rockies belts, (4) significance of the fracture systems, (5) Cenozoic erosional history and basin sedimentation, and (6) paleodynamics of the rock fluids. End_of_Article - Last_Page 790------------