NEW MODEL FOR EVOLUTION OF FOLD-AND-THRUST BELT CURVATURE BASED ON INTEGRATED STRUCTURAL AND PALEOMAGNETIC RESULTS FROM THE PENNSYLVANIA SALIENT

In a number of curved fold and thrust belts worldwide, such as the Can tabrian are and the Wyoming-Idaho salient, paleomagnetic data indicate vertical axis rotations inconsistent with structural findings, This a pparent conflict is especially pronounced in the Pennsylvania salient, where the paleomagnetically defined vertical axis rotations are oppos ite of the rotation sense indicated by structural studies, We resolve this apparent disparity by developing an integrated and kinematically admissible model that has implications for other curved mountain belts . The curvature of the Pennsylvania salient may be explained by deform ation partitioning in an initially laterally tapered basin between the Cambrian-Ordovician carbonates and the overlying siliciclastic rocks, Earliest deformation occurred in the lowest strata and progressed tow ard the foreland and up section with time. Lateral differences in init ial layer-parallel shortening in the Cambrian-Ordovician carbonates ca used differential translation and rotations about a vertical axis in t he cover sequence. Because of initial basin geometry, the orogenic wed ge developed a lateral taper, With further shortening in the wedge and involvement of the cover rocks in the fold and thrust deformation, gr avitational driving forces became more important, and the paleostress trajectories diverged in opposite directions on the two arms of the sa lient in response to the lateral taper.