THE MIDCONTINENT EXPOSED: GIS MAPS DEPICTING CRATONIC FAULT-AND-FOLD ZONES, AND STRUCTURE CONTOURS ON THE BASEMENT-COVER UNCONFORMITY, IN THE NORTH AMERICAN CONTINENTAL INTERIOR, AS A CONTEXT FOR INTERPRETING EARTHSCOPE SEISMIC STUDIES

The Midcontinent region of the United States is part of the continental-interior platform region of the North American craton. Its Precambrian basement includes Archean nuclei as well as Proterozoic convergent-accretionary orogens. The region was also affected by Proterozoic anorogenic igneous events and by Proterozoic rifting. At the end of the Precambrian, erosion produced a continent-wide unconformity, the "great unconformity," that serves as an ideal marker surface for characterizing the epeirogenic movements (broad, gradual upwarps and downwarps) of the lithosphere's surface that yielded intracratonic basins, domes, and arches. Phanerozoic strata, which has varying thickness, covers most of the Precambrian basement. Offset and folding of marker horizons within these strata indicate that faults throughout the craton underwent pulses of reactivation during the Phanerozoic. In association with our EarthScope Flexible Array project (OIINK), we are producing two maps: (1) a shaded-relief structure-contour map on the top surface of the Precambrian basement (i.e., on the great unconformity); and (2) a map showing the positions of fault-and-fold zones that likely have a Precambrian ancestry but have been reactivated during the Phanerozoic. The region covered by our map extends from the Appalachian front on the east to the Wasatch front on the west and will include all regions underlain by cratonic crust in the United States (i.e., the Midcontinent, the Rocky Mountains, and the Colorado Plateau). The maps will provide a 3-D visualization of epeirogenic features, and will illustrate the relationship between these features and fault-and-fold zones. These maps are being prepared using ArcGIS, and will ultimately be made available in downloadable form. By overlaying other data sets (magnetic anomalies, gravity anomalies, heat flow, seismicity, bedrock geology, etc.) on our maps, it will be possible to characterize the craton in a manner that can provide a foundation for interpreting new EarthScope seismic-tomography and micro-seismicity data, as it becomes available. Thus, the maps will provide insight into relationships between deep-crustal and mantle inhomogeneities and boundaries, and upper-crustal geologic features.