TECTONIC AND MAGMATIC EVOLUTION IN THE ANDEAN BELT IN NORTHERN AND CENTRAL CHILE

The Andean Orogen in Chile derives from the ~550 m.y. geological history of a 4000 km long continental margin and reflects interaction between lithospheric plates during continental assembly and break-up. In terms of the paleogeographic, magmatic and sedimentologic evolution, it can be subdivided into 5 “tectonic cycles”: 1. Pampean (Pre to Early Cambrian), with little information in Chile. 2. Famatinian (Ordovician), characterized in southwestern South America by deformation events assigned to repeated collisions between Gondwana and Laurentia. These two cycles correspond to the post-Rodinia break-up stage. 3. Gondwanan (Late Paleozoic), corresponding to the assembly of Gondwana where the margin of South America hosted typical arc magmatism and a subduction complex in the forearc. This cycle ended with a strong contractional phase that caused crustal thickening allowing deep crustal melt generation. 4. Pre-Andean (latest Permian to earliest Jurassic), corresponding to an episode of ceased subduction during final assembly and initial stages of Gondwana break-up, widespread tectonic extension, and abundant bimodal magmatism with the involvement of crustal and mantle sources. 5. Andean (late Early Jurassic - Present), characterized by continental break-up and representing the archetypal example of a subduction related mountain belt with an associated volcanic arc. Corresponding magmas record the involvement of mantle, crustal and subduction components and repeated changes in geodynamic extensional and compressional conditions. Superimposed on this evolution were more unusual events such as: Subduction of passive and active ridges, changes in plate geometry and dynamics, and development of an aulacogen and a second huge felsic magmatic province in southern Chile.

The history of the Andean orogen has shown long episodes of extension along the arc separated by episodes of contractional deformation associated with modifications in plate dynamics and geometry. Continental accretion and erosion, and positioning of the arc and its associated forearc and backarc areas are strongly dependent on the fluctuations in plate dynamics. Major strike-slip fault systems appear to have been controlled by the location of the magmatic arc, and their movement mainly controlled by the obliquity of convergence.