Process and Timing of Exhumation in the Ozark Plateau, Missouri  

Sarah Brown, University of Illinois Urbana-Champaign, Department of Geology, Urbana, Illinois, United States, [email protected]

The Ozark Plateau is a 150,000 sq km intracratonic uplift located in the mid-continent region of the United States. Though the region has subdued topography, structural relief between the high point of the plateau and the low point of the adjacent Illinois basin, is over 7.5 km, comparable to the elevation of major mountain belts. Stratigraphic data suggests that the uplift has remained high throughout the Phanerozoic, but it was probably submerged as recently as the Mississippian. Thus, it has risen by a few hundred meters since the end of the Paleozoic. The origin of this exhumation, and of comparable exhumations in other continental interiors, remains unknown. Unlike the Tibet Plateau or the Colorado Plateau, the Ozark Plateau does not occur at, or near, a tectonically active plate boundary.

Research suggests that formation and persistence of the uplift reflects multiple phenomena throughout time. It is not clear whether the present-day elevations are a residual of earlier exhumation or post-Paleozoic exhumation due to renewed movement on border faults. Procedures used to test exhumation models of the Ozarks include computer flexural modeling, and apatite fission track dating to: create a thermal history of the area; learn exhumation history through blocking temps; and constrain the age of the exhumation. Research indicates that a portion of the exhumation is less than 250 m.y.; the renewed displacement may be associated with Cenozoic mid-plate seismicity. By determining the structure of the block, and its exhumation history, we are able to help constrain the different origin theories.