The early Andean arc in Southern Central Chile and Argentina is a main feature of the youngest Andean margin paleogeography, acting as the western edge of the Neuquen Basin sedimentation and sometimes as a barrier to the connection between the open sea and the back-arc basin. Earlier stages of evolution of the magmatic arc are probably related to three pulses of magmatism. The first is related to S-type granites with slightly subduction features and apparently contemporaneous intermediate to highly differentiated volcanic rocks during Late Triassic (similar to 225-220 Ma), that probably represent the first event of magmatism in the area since the Carboniferous. A second is more diverse, with bimodal features, presence of Atype granites and more developed calc-alkaline affinities that took place during the Triassic-Jurassic boundary (210-197 Ma). This event is developed as a paired belt of intrusive outcrops in the present Coastal Cordillera and volcanic deposits in the proximities of the Chile-Argentina border, suggesting an arc-back-arc configuration which is most likely a submerged or slightly emerged immature arc. Finally, the third and definitive instauration and development of the Andean Arc seems to have taken place since late Lower Jurassic, with the development of larger granitic bodies and thick volcanic sequences well exposed in the Coastal Cordillera between 33 degrees and 35 degrees S and close to the Chile-Argentina border between 38 degrees and 40 degrees S. Geochemical and isotopically available data suggest that this early arc was emplaced and evolved through a thin crust with none to little contribution of it during the magma genesis.