SOME NEW OBSERVATIONS CONCERNING THE NATURE AND EXTENT OF RIFTING IN THE MID-CONTINENT REGION

A variety of geophysical data, including newly released 3-D seismic reflection data, show us that the basement structure of the Mid-Continent region is very complex. The dimensions of many of these basement structures is very large by global standards, and thus, they are a tectonic puzzle because of their size, structural complexity, and distance from active plate margins that usually make the driving mechanisms for intraplate deformation evident. The crust of the Mid-Continent region formed during a period of continental growth that extended from about 1.8 to 0.9 Ga. The impressive Mid-Continent rift system (MCRS) tried to interrupt this period of continental growth at about 1.1 Ga but failed even though it modified the crust massively. However, the supercontinent resulting from this growth did not survive long and began to break up by ~700 Ma. This period of rifting established the structural framework of the southern Mid-Continent region, subsequent Early Paleozoic basin development, and at least partly, the formation of the Ancestral Rocky Mountains in the late Paleozoic. The Southern Oklahoma aulacogen (SOA) is an impressive example of this rifting event. The deformation that formed the Ancestral Rocky Mountains often resulted in massive inversion of SOA rift structures and magmatism and is due to a plate collision in the late Paleozoic whose origin is under debate.