INTERPLAY BETWEEN VOLCANISM, TECTONICS, GEOMORPHOLOGY AND MINERALIZATION: THE CASE FROM THE ANDES BETWEEN 27°– 28°S AND 66°– 69°W

The Andean region between 27°- 28°S and 66° - 69°W in E. Chile and W. Argentina provides important clues for understanding the interplay between Cenozoic magmatism, tectonics, geomorphology and mineralization processes. This segment represents the southern end of the Central Volcanic Zone (CVZ), where there is a transition to flat-slab subduction and a broadening of the Miocene volcanic arc following south-eastern trending regional lineaments. Important epithermal deposits and Cu-bearing porphyries (Maricunga Belt on the west, Farallón Negro Volcanic Complex on the east) are associated with the Cenozoic volcanism.

Since the Late Oligocene this region has undergone five major volcanic events related to basin formation: 1) an Oligocene-Lower Miocene magmatic stage in the Maricunga belt (27-17 Ma); 2) a Middle Miocene event (17-11 Ma); 3) a Late Miocene volcanic arc, which migrated and broadened to the east (11-5 Ma) reaching a zenith ca. 7 Ma; 4) Pliocene contraction of the volcanic arc (5-1.8 Ma); and 5) development of a Quaternary volcanic arc.

Two different geomorphologic environments are also recognised in this region. The most prominent is the Andean setting along the western side composed of the Cordillera Frontal, Precordillera and Famatina morphotectonic units which are strongly influenced by high rates of tectonic uplift and denudation and it is this interplay that has dominated landscape development since the Late Miocene. In the eastern part of the region, the morphology is controlled by an intraplate setting with the Sierras Pampeanas characterized by well-preserved erosion surfaces.

A set of sinistral NW-SE regional structures (e.g. Valle Ancho lineament), cross the Andes and are cut by dextral ones running SW-NE (e.g. Tucumán transfer zone). The cross cutting relations and structures suggest a clockwise rotation of Sierras Pampeanas block. Overthrusting, uplift and erosion rates were diachronous in the different morphotectonic units across the region. Epithermal and porphyry copper deposits appear to be associated with brief erosive periods following uplift events.