Tectonic setting

The western rim of the South American Plate has been the locale of terrane accretions, collisions, and various subduction dynamics. Subduction first occurred following the breakup of Rodinia in the Late Proterozoic, and since then there have been numerous phases of rifting and subduction re-activation (e.g. Ramos, 2009). Intraplate magmatism and extension was focused along the sutures between the accreted terranes and the cratonic zones of central South America during the Triassic, while subduction initiated along the Andean margin in the Early Jurassic, coeval with the breakup of Gondwana (Ramos, 2009). Development of the modern Andes commenced during the Cretaceous, under a convergent boundary not dissimilar to the Laramide orogeny of North America.

Northern Andes

The Northern Andes are located on the plate boundary between the Nazca and Caribbean Plates, and the northwestern basement of South America. Adjoining this basement is the Western Cordillera terranes, comprising dextrally sheared (e.g. Kennan and Pindell, 2009) slices of oceanic plateau and island arc volcanics (e.g. Kerr et al. 2003), and related sedimentary units. For this reconstruction we have followed Ramos (2009) and incorporated the Choco, Dagua-Pinon, Amaime, Tahami, and Chibcha terranes (Figure 1). The relationships of these Western Cordillera terranes suggest a Caribbean origin (Kennan and Pindell, 2009).

Central Andes and the Bolivian Orocline

The Central Andes is predominately comprised of deformed Paleozoic accreted terranes, situated along the western margin of the Amazonian Craton and the Grenville-aged Pampian terrane (Figure 1). Deformation in this region has been the consequence of orogen-normal shortening (Isacks 1988; Allmendinger et al. 1997; Kley and Monaldi 1998), and resulted in the formation of an extraordinary geological feature - the Bolivian Orocline (e.g. Isacks, 1988). This is an archetypal example of orocline formation, whereby an initially linear orogen is deformed into a more curved geometry in plan view as the result of tectonic processes (Carey, 1955), such as stagnation, indentation, and trench advance at the centre of the orogen, and slab rollback to its north and south (Schellart, 2008). The oroclinal curvature is also expressed by the pattern of block rotations as revealed by palaeomagnetic data, with counterclockwise rotations in southern Peru clockwise in northern Chile (e.g. Beck, 2004). For this region we have segregated the tectonic boundaries for the reconstruction based on Ramos (2009).

Figure 1. Tectonic map of the Andean margin of South America.

Tectonic map of the Andean margin of South America.

Northern Andean terranes compiled from Ramos (2009) and (Kennan and Pindell, 2009). Central Andean terranes modified from Ramos (2009). The Gastre Fault System separates Patagonia and Southern Patagonia from mainland South America, and is based off Rapela and Pankhurst (1992). Cratonic regions are modified from Fuck et al. (2008), and are named as follows: (1) Amazonian Craton, (2) Inferred extent of Amazonian Craton, (3) Sao Luis Craton, (4) Borborema Province, (5) Parnaiba Block, (6) Sao Francisco Craton, (7) Paranapanema Block, (8) Rio de la Plata Craton, (9) Pampia Terrane. Stippled region represents present-day South America, cross-hatched region represents continental shelf, while the red-yellow striped zone symbolizes the area of the Cordillera Darwin Complex and Rocas Verdes Basin basalts. For the Inferred extent of Amazonian Craton, (2), and Pampia Terrane, (9), we follow Fuck et al. (2008) in that they are high grade metamorphic rocks of an "uncertain" tectonic setting, and formed approximately between 1300–1100 Ma.

Southern Andes and the Patagonian Orocline

The southern extremity of the Andean system forms a dramatic change in the structural trend by an angle of approximately 90°, known as the Patagonian Orocline (Carey, 1955) (Figure 1). Palaeomagnetic studies of the region appear to confirm the orogen has been rotated with respect to stable South America (Burns et al. 1980; Cunningham et al. 1991; Beck et al. 2000; Rapalini et al. 2001; Iglesia Llanos et al. 2003). In addition to the orocline, a belt of basic rocks in the back arc region (Dalziel et al. 1974), and a Mesozoic high-grade metamorphic core (Dalziel, 1981; Dalziel and Brown, 1989; Kohn et al. 1995), also distinguish the region.