Basement Structures in the Midcontinent Region: Some Perspectives Based on Regional Geophysical Data

G. Randy Keller.  School of Geology and Geophysics, University of Oklahoma, Norman, OK 73019  [email protected]

A variety of geophysical data show us that the basement structure of the midcontinent region is very complex. Most of this complexity involves structures that are less than 1.1 billion years old and many are Phanerozoic in age. The dimensions of many of these structures is very large by any measure, 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 continental crust of the midcontinent region as we recognize it today is due to a period of continental growth that extended from about 1.8 to 1.0 Ga. However, the resulting supercontinent did not last long and began to break up by ~700 Ma. This period of rifting established the structural framework of the southern midcontinent region, the subsequent early Paleozoic basin development, and, at least partly, the formation of the Ancestral Rocky Mountains in the late Paleozoic. These events, the Laramide orogeny and the late Cenozoic uplift to the west, are topics of great current scientific interest. Emphasis on the use of gravity, magnetic, and remote-sensing data in studies of the midcontinent region has increased, and these data have been particularly effective when used in an integrated fashion with seismic and drilling data. These studies have shown that rifting during the late Precambrian and Cambrian affected large areas of the midcontinent region and created sedimentary basins that have in many cases survived to the present and are underexplored. In addition, younger structures such as those associated with the Ancestral Rocky Mountains have often been affected by older rift structures preserving Cambrian and older strata. The deformation that formed the Ancestral Rocky Mountains is often a massive inversion of these rift structures and is due to a plate collision in the late Paleozoic. These studies show that we are still learning about the structure and history of the basement in the midcontinent region and the implications for the discovery of further petroleum resources.