KELLER, G. RANDY, and KATE C. MILLER , Department of Geological Science, University of Texas at El Paso, El Paso, Texas 79968

ABSTRACT: Structure and Evolution of the Precambrian Basement in the Southern Rocky Mountain Region

Because of its interesting geologic history and natural resources, the Southern Rocky Mountain region has been the focus of many geological and geophysical studies. The Precambrian basement has been a target of much recent interest. The control of basement structures on younger features is well established and late Precambrian sedimentary rocks have been exploration targets. The crust of in this region gradually formed as a series of middle and late Proterozoic orogenic events creating bands of accreted crust that added material to the then growing continent. During this period of accretion, a widespread phase of magmatic activity resulted in the emplacement of vast quantities of both intrusive and extrusive igneous rocks at about 1.4 Ma. To the south in Texas, the Grenville orogeny at about 1.0 Ga marked the end of this major period of continental growth. Perhaps as a result of this last phase of accretion, a widespread period of extension effected the region This period of continental growth was a part of the formation of the supercontinent Rodinia and as the Precambrian era came to a close, Rodinia broke up during a major episode of rifting that formed a passive continental margin along the Ouachita trend that follows a sinuous course across Texas and northern Mexico. These two rifting events formed the structural framework for the development of many of the petroleum provinces in the region. The relative tranquility of the early Paleozoic era was interrupted by the formation of the Ancestral Rocky Mountains during Mississippian and Pennsylvanian time that was heavily influenced by older structures. Another period of quiescence followed and ended with the Laramide orogeny and the region has been tectonically active ever since.

AAPG Search and Discovery Article #90915©2000 AAPG Rocky Mountain Section, Albuquerque, New Mexico