BASEMENT CONTROL ON PHANEROZOIC STRUCTURES AND TECTONICS - MIDCONTINENT USA

Modern-day structures of Midcontinent USA are relatively well known due to extensive surface mapping and individual state documentation of the geologic records from exploration for petroleum. The broader tectonic system that controlled these structures is revealed by geophysical data and the stratigraphic patterns of deposition and erosion through the Phanerozoic. The trends of most Phanerozoic structures, particularly those that exhibit repetitive movement, reflect the rejuvenation of the original architecture of the basement rather than a true directional response to the stress pattern imposed during any particular time frame.

In Midcontinent USA, much of the basement is contained within the Central Plains orogen and within the Transcontinental Proterozoic belt. This basement consists of a series of island arc terranes accreted during the period 1.8 to 1.6 Ga. Each arc within the series is delineated by an accretionary suture that has remained as a deep-seated zone of weakness in the basement. Four major island arc terranes and their bounding sutures are identified in Nebraska and adjacent areas. These sutures were reactivated into important Phanerozoic positive structures such as the White River fault system, the Wattenberg high, the Cambridge arch, the North Platte arch, the Ord arch, the Central Kansas uplift, the Rush rib, and the Las Animas arch.

The Proterozoic accretionary process also indirectly created the Nemaha boundary zone. This zone controlled a portion of the Midcontinent rift system (1.1 Ga) and the Phanerozoic Nemaha Uplift. In the Nebraska region the Midcontinent rift system, and to some extent the older sutures, controlled the consecutive development of the Southeast Nebraska arch, the North Kansas basin, the Nemaha uplift, the Forest City basin, the Abilene anticline, and the Table Rock arch. Interrelating the stratigraphic studies of the Phanerozoic with the tectonic research on the Precambrian basement provides the insight necessary to explain and further understand the structures of Midcontinent USA.