Surface Manifestation of the Ste. Genevieve Fault Zone, Missouri: Polyphase Kinematics, and Landscape Rejuvenation, along the Ozark Plateau / Illinois Basin Boundary
Monday, 14 December 2015
Poster Hall (Moscone South)
The Ste. Genevieve Fault Zone (SGFZ) runs from SE Missouri into SW Illinois, in the cratonic platform of North America. This NW-trending, 190 km-long belt separates the Illinois Basin from the Ozark Dome and has served as a tectonically significant crustal boundary throughout the Phanerozoic. Data obtained from OIINK (part of EarthScope), a seismometer array that extended from the central Ozark Plateau into Kentucky, indicates that the SGFZ is more seismically active than previously recognized. A subsurface DEM of the Great Unconformity (the contact between Precambrian basement and Paleozoic strata) shows that the fault zone roughly overlies 7 km of structural relief. Interpretation of OIINK data shows that there are likely deeper crustal manifestations of the SGFZ. A recompilation of surface geological mapping of the SGFZ, coupled with new mapping of structures exposed in roadcuts along the NE corner of the Ozark Plateau, suggests that the SGFZ is a broader structure than previously observed. The complex configuration of fault traces supports a model in which the fault zone has accommodated more than one phase of transpressional and transtensional reactivation during the Phanerozoic. The SGFZ includes many splays, some of which die out up-dip in monoclinal folds whose traces control local topography. The facing of the folds indicates that some of these splays dip northeast, though the pattern of regional uplift, by analogy to uplift in the Colorado Plateau, suggests that the master fault of the SGFZ dips southwest. This association supports models in which synthetic and antithetic splays of the SGFZ locally delineate positive flower structures. LIDAR-based maps suggest the plateau was rejuvenated after the establishment of meandering streams, for a set of incised meanders serve as the local base level for subsequent dendritic drainage networks. The landscape therefore may have been affected by a phase of post-Paleozoic uplift, a hypothesis currently being tested by U/Th-He thermochronology.