THREE-PHASE LATE PALEOZOIC DEFORMATION OF THE SOUTHERN OZARK DOME, WESTERN BUFFALO RIVER REGION, NORTHERN ARKANSAS

Recent geologic mapping and kinematic studies within Ordovician-Pennsylvanian sedimentary rocks in the western Buffalo River region reveal three phases of late Paleozoic deformation in the southern Ozark dome. Early ENE-directed shortening, D1, was followed by N- to NNE-directed extension, D2, and then by N- to NNW-directed shortening, D3. D1 accommodated localized ENE shortening in the >4-km-long Kyles Landing reverse fault and associated fold. This structure deforms upper Mississippian strata but is unconformably overlain by lower Pennsylvanian strata. D2, N- to NNE-extension, was widespread in the area and recorded by WSW- to WNW-striking normal faults, NE-striking dextral strike-slip faults, and variably oriented monoclinal folds. D2 deformation affects lower Pennsylvanian strata but is older than probable Early Permian lead-zinc mineralization that was localized along D2 faults. Finally, during D3 deformation, selected D2 structures were reactivated to accommodate N- to NNW-directed shortening. D3 reactivation of the SSE-dipping Compton normal fault is indicated, in its hanging wall, by the presence of small strike-slip faults that cross cut D2 extensional deformation bands and, in its footwall, by the presence of an ENE-elongate anticline cored by a small thrust fault having a 170° slip azimuth. Regionally in northern Arkansas, D3 is recorded by N- to NNW-directed compression axes in published calcite-twin studies and by a prominent joint set.

Multiphase deformation of the western Buffalo River region is interpreted as a midcontinent response to evolving Late Paleozoic continent-margin orogenic belts. Speculatively, D1 reflects late Mississippian-early Pennsylvanian shortening due to far-field stresses radiating from an initial Alleghanian-Ouachita indentation of the southeast continent margin. D2 extension reflects Pennsylvanian down-flexure of the southern continent margin adjacent to the growing Ouachita thrust load, and D3 reflects shortening during final Permian closure of the Ouachita orogenic belt.