MODIFICATION OF THE ARBUCKLE ANTICLINE HINGE ZONE BY STRUCTURES ASSOCIATED WITH THE CHAPMAN RANCH THRUST AND THE COLLINGS RANCH FAULT, ARBUCKLE MOUNTAINS, OKLAHOMA

The Arbuckle Anticline in southern Oklahoma is a NW-trending fold that forms part of the central portion of the Arbuckle Mountains. The anticline was formed during a Paleozoic Wilson cycle that ended with the convergence of Gondwana and Laurasia and resulted in the development of a fold and thrust belt. The trend of the anticline is orthogonal to the Ouachita-Marathon orogeny and follows a Proterozoic aulacogen. The hinge of the Arbuckle Anticline is thought to be affected by the Collings Ranch Fault on the northern part and by the Chapman Ranch Thrust on the southern part. Strikes and dips of bedding planes of the hinge zone exposed at the Interstate 35 were measured, as well as the trend and plunge of mesoscopic folds, thrusts and normal faults. The geometrical relationships between these structural elements were examined using standard stereonet. These were used in connection with structural interpretation of panoramic photographs spanning the exposed outcrop, as well as close-up photographs. These showed the mesoscopic structures such as folds, normal and thrust faults that deform the hinge zone of the Arbuckle Anticline. Our analysis indicate that: (1) The hinge of the Arbuckle Anticline is affected by N-verging mesoscopic thrusts that are parallel in orientation to the Chapman Ranch Thrust to the south; (2) The hinge zone is also affected by a series of normal faults of different orientations that might be associated with the Collings Ranch Fault to the north; (3) Thrusting might be closely associated with folding, but normal faults might have evolved at a later deformation event.