FAR-FIELD LATE PALEOZOIC INTRAPLATE DEFORMATION IN THE MIDCONTINENT: IMPLICATIONS FOR COLLISION ALONG THE SOUTHEASTERN MARGIN OF THE NORTH AMERICAM PLATE

Complex plate collisions along the southern and eastern margins of the North American Plate during the late Paleozoic produced far-field deformation in the intraplate midcontinent region. Coaxial paleo-stress orientations are determined for this far-field deformation from analysis of strain and fault kinematics along four major intraplate structures: Cap au Gres faulted monocline, Ste. Genevieve fault zone, faults overlying the Commerce Geophysical Lineament (CGL) in the Thebes Gap area, and folds and faults associated with the Pascola arch, which includes the present-day New Madrid seismic zone. Analysis of these four structures shows that maximum horizontal stress S(Hmax) was oriented roughly NE-SW during Late Mississippian to Middle Pennsylvanian time and that deformation was relatively major. However, during Late Pennsylvanian (and Permian?) time, the orientation of S(Hmax) shifted to NW-SE along the Cap au Gres and Ste. Genevieve structures, and to nearly E-W along the CGL and Pascola Arch. Deformation along the first two structures was relatively minor, but was major along the latter two structures and particularly along the Pascola Arch in the vicinity of the New Madrid seismic zone. These interpreted orientations and change in S(Hmax) are consistent with a regional stress-field model in which first a northwest-moving Ouachita block indents the North American Plate [producing NE-SW S(Hmax) in intraplate region] and is then followed by cratonic collision along a NE-trending front in the southern Appalachian region [producing NW-SE to E-W S(Hmax) in intraplate region].