The relevant characteristic of the evolution of the Pacific continental margin of South America during the Mesozoic-Early Cenozoic has been tectonic segmentation. This has controlled suc- cesive episodes of sedimentary accumula- tion, extrusive and intrusive magmatism and deformation that ocurred at conver- vergent plate edges. During this inter- val, at least three main transverse boundaries played an important role conditioning the existence of paleo- segments of different longitudinal extent at various Periods. These probably correspond to deep-seated faults in the Huancabamba Deflection and at the Arica- Santa Cruz Line; the third boundary projects westward to the Chile Ridge._x000D_
Tectonic activity appears to have been continous at the Huancabamba Deflection at least since the Triassic. The Arica- Santa Cruz Line was probably an active boundary during the Triassic and Cretaceous; the southernmost boundary may have started to be active at the end of the Jurassic. This tectonic activity has determined the subsidence - uplift and paleogeographic conditions of the paleosegments.