Extrusion driven collision is controlled by strike-slip faults of opposite senses whereas subduction related oblique convergence is accommodated by margin parallel faults of identical senses. Northern Andes geodynamics has been interpreted either as resulting from the obliquity of convergence between Nazca and South American plates or from the collision of the Carnegie Ridge with Ecuadorian margin. The sense of the Cauca-Patia and Romeral Fault System (CPRFS) has been interpreted in two opposite manners: right or left-lateral agreeing with oblique or collisional patterns, respectively. We analyze arguments which favor, South to 4¿N, a right-lateral motion along the CPRFS that is consistent with obliquity driven geodynamics. However, North of 5¿N, the CPRFS is actually left-lateral. These opposite motions between the northern and southern part of the CPRFS have to be accommodated around 5¿N by N-S stretching and/or shortening. Existing data support N-S shortening around 5¿N, this buttressing could be due to the collision between the Panama and Andean Blocks. ¿ American Geophysical Union 1995