Implications of the North and South Panama Thrust Belts for the origin of the Panama Orocline

High resolution imaging of the north (NPTB) and south Panama thrust belts, using the SeaMARC II seafloor mapping system and digital seismic reflection profiling, provides an excellent data base with which to determine the kinematics of oroclinal deformation of Panama. Remarkable continuity of structural orientations over 300 km along the NPTB argues for widespread uniformity in direction of thrusting between Panama and the Caribbean plate. Westward decrease in the width and height of the accretionary wedge indicates a westward decrease in the total amount of convergence. Two major cross faults cut the wedge in its eastern part, forming two minor blocks with different relative motions with respect to the Caribbean. Frontal thrust orientations change across these faults. Major faults have been proposed to cut the isthmus of Panama, but simple cross‐isthmus faulting alone cannot explain the orientations of the major thrusts of the NPTB. Bending of a flexible beam can explain much of the observed structure, both directions and rates, though the scale of the orocline precludes considering this as an elastic phenomenon. Plastic deformation of Panama may be a useful mechanical explanation, at least for eastern Panama, but consideration of plastic slip lines must include the northern Andes as well. Changing from more rigid, blocklike offsets on faults in western Panama to a continuum of strain in eastern Panama may be the best explanation for observations at present.