Documenting Translation and Vertical - Axis Rotations using Paleomagnetic Techniques along the Panama Isthmus : Preliminary Results 43

Along the Isthmus of Panama 23 paleomagnetic sites were sampled in order to determine preliminary block rotations and paleolatitudinal movements. The lithology selected for this research corresponds to volcanic and sedimentary rocks with ages ranging from Upper Cretaceous to Pleistocene. Counterclockwise vertical axis rotations were uncovered in Paleocene and Oligocene units separated by a sinistral fault. Mean directions of two sites collected in Cenozoic rocks to the north of the fault are westerly (D 275.4, I -20.8, k 20.46, a95 10.9; D 264.6, I 5.3, k 292.35, a95 3.5), whereas the mean direction uncovered in one site collected in Oligocene rocks to the south of the fault yields a northward declination and positive inclination (D 346.3, I 14.3, k 18.43, a95 14.4). Vertical axis rotation of 81.7o ± 13.3o, of the Paleocene rocks with respect to the Oligocene rock. Cenozoic sites record the northward path of the trailing edge of the Caribbean plate, from 10.8oS for Paleocene to 6.6oN for Oligocene. However, more sites are needed to be collected in order to better constraint this northward translation. Components isolated in El Valle volcano and Canal areas using Middle Miocene to Pleistocene rocks, indicate normal and reverse directions similar to the current direction of the Earth magnetic field. Therefore, no major latitudinal displacement of the Panama Isthmus has occurred during the Neogene. Northward migration of the Panama arc is consistent with the Pacific origin of the Caribbean plate and counter-clockwise vertical axis rotation of several blocks in Panama could be related with the South American Plate collision since Pliocene.