ON THE INFLUENCE OF INHERITED PRECAMBRIAN AND PALEOZOIC PALEOGEOGRAPHIC PATTERNS ON PHANEROZOIC MOUNTAIN BUILDING IN THE SOUTHERN CENTRAL ANDES

During the entire Phanerozoic the western margin of South America has been facing the open ocean. In the southern Central Andes, most of this time active margin processes governed the style of basin development, deformation, magmatism, and metamorphism. An exception is very likely the Silurian to Early Carboniferous interval for which a passive margin setting is suggested. It has been a long accepted view that depocenters and magmatic arcs migrated westward during the Paleozoic, and eastward in the Mesozoic and Cenozoic. This seemed to suggest continental growth by terrane accretion during the Paleozoic. This view was strongly influenced by the recognition of the accretion of exotic terranes to this margin south of c. 27°S during the Paleozoic. Generally, terrane bounding faults and sutures represent first order crustal discontinuities. Regarding the southern Central Andes, however, most, if not all, of the proposed Paleozoic terrane boundaries failed their tests. A re-examination of the basic tenet of westward migration of basins and arcs during the Paleozoic demonstrates that the Ordovician continental magmatic arc, the subsequent Late Ordovician Oclóyic orogen acting as the Arco Puneño positive area in the Silurian to Early Carboniferous, and the Late Carboniferous-Permian continental magmatic arc all occupy essentially the same area. These elements are now contained within the Cenozoic continental arc. Paleozoic basins and depocenters are also located in relatively constant positions east and west of arcs and Arco Puneño. The same holds true for the position of subduction trenches in the Ordovician, Late Carboniferous and the Cenozoic. Only during the Jurassic and Cretaceous was the trench located outboard of the present-day continental margin. This Mesozoic fore-arc has been eroded since by subduction erosion. The maintenance of relatively fixed positions of arcs, peri-arc basins and trenches during the Paleozoic and Cenozoic suggests that their location and evolution has been controlled by major and persistent custal-scale structures inherited from the pre-existing Precambrian crust.