REFLECTIONS ON THE COMPLEX STRUCTURE AND TECTONIC EVOLUTION OF THE MID-CONTINENT REGION, USA

The structure and evolution of the Mid-Continent region of the USA remains a mystery in many respects because of the scarcity of outcrops of the basement and lower Paleozoic units, deep drilling results, and deep geophysical results. Some new 3-D seismic reflection data have been released for analysis, and the results show interesting new details about the relationships between Paleozoic and Precambrian structures, as well as, the impressive dimensions of many of the structures present. This is particularly true in the southern Mid-Continent region where the complexity of the triple junction between the classic Southern Oklahoma Aulacogen (SOA) that extends from northeast Texas to southern Colorado and the relationship of Cambrian margin of North America with the Ouachita Orogenic Belt (OBB) have been refined. In addition, many aspects of the tectonic history of the Ouachita and Variscan orogens are similar, and in a tectonic sense, they are geographically linked, because at the end of the Paleozoic, one could travel from west Texas to southern Poland following a continuous orogenic belt. Several crustal blocks have been proposed to be exotic relative to the cratonal core of the region, and specifically, the Sabine terrane and Llano uplift have been identified by the integration of geological and geophysical data and share similarities with features such as the Bohemian Massif in Central Europe. Rifting has also played a major role in the evolution of the region with the Mid-Continent Rift (MCR) being a particularly impressive feature. Recent results question the long-held view that it is a failed rift and suggest that Great Lakes region of this rift was also the site of a large igneous province. Cambrian rifting also affected much of the Mid-Continent region and played a major role in the evolution of important petroleum provinces.