CENTRAL PLAINS OROGEN - ACCRETIONARY CORE OF THE NORTH AMERICAN TRANSCONTINENTAL PROTEROZOIC PROVINCE

The southern limit of North America at about 1.8 billion (Ga) years ago was defined by the Wyoming, TransHudson, Superior, and Penokean provinces. The southward expansion of North America during the next several hundred million years has been characterized broadly as the Transcontinental Proterozic province consisting generally of the Yavapai-Mazatzal in the southwest, the Central Plains orogen (CPO) in the center and less clearly defined subprovinces along the southeastern margin. This accretionary terrane is bordered on the south by the Granite-Rhyolite province.

The CPO in the Nebraska region records southward growth by a series of accretionary terranes (Dawes, 1.78 Ga; Frontier, 1.71 Ga; Hitchcock, 1.67 Ga, Western Kansas, 1.61) based on basement rock type, geophysics, and tectonic trends. Similar patterns of accretionary growth can be extended eastward along the southern boundary of the Penokean orogen to include the Southern Iowa, Northern Missouri, and Central Missouri terranes. These eastern accretionary units are a southward continuation of the process that formed the Penokean orogen (1.84 Ga). The boundary relationships between this family of arcs and those in the western CPO is unclear although the ages of accretion are similar.

All of these terranes within the CPO represent a series of island arcs progressively accreting to enlarge North America. The terrane boundaries are in part defined by Phanerozoic structures representing reactivation of accretionary sutures. Eastward, the Transcontinental Proterozoic province seems to lose this record of accretionary history and consists of an eastern equivalent of the Granite-Rhyolite province (1.5-1.35 Ga) that forms the southern boundary of the CPO.