Structures Associated with Southern Extension of Mid-Continent Rift System in Kansas: ABSTRACT

Distinct geophysical anomalies and attendant rock types of the Mid-Continent rift system (MRS) can be traced southwestward from the Great Lakes region into southern Kansas. Rocks and structural deformation linked to rifting in Kansas occur in a north-northeast-trending 150 km-wide zone. A 50 km-long separation in southeastern Nebraska devoid of rift-derived rocks is related to a crosscutting transform fault or tectonic zone that extends several hundred miles northwest-southeast. Precambrian sedimentary rocks of the MRS occur in fault-bounded basins on either side of a central horst and are derived from the horst and from nearby granitic highlands. North-northeast-trending faults dominate the structure within the MRS in Kansas, but possibly older northwest-trending structures are also important in determining the size, shape, and stratigraphy of individual horst blocks and basins. Both sets of faults were intermittently reactivated, with latest movements recorded within the Phanerozoic sedimentary sequence. Domal culminations and rhomboidal grabens also are recognized along the trend of the MRS, some serving as traps for petroleum accumulation. North-northeast-trending faults show Phanerozoic vertical displacement up to 600 m along the Humboldt fault system. Left-lateral motion (up to 15 km) during the Late Mississippian-Early Pennsylvanian along northwest-trending faults is also suggested. Oil fields producing frommore » several Phanerozoic reservoirs are located along north-northeast-trending structures subparallel to the MRS. Several structures are arranged in left-stepping en echelon patterns.« less