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The late pre-Andean tectonics of the western margin of the South America plate (SAM) has been activesince the late Jurassic to the Paleogene, interacting with the Aluk plate in the Cretaceous, the Aluk-Farallon-SAM triple junction and Farallon plate in the Paleogene.There is agreement on the relationship for subduction with respect to SAM of the Aluk plate in theCretaceous, and for the Nazca plate in the Neogene, but the fate of the Aluk-Farallon-SAM triple junctionin the Paleogene, has been subject to different interpretations that span from a) the uninterruptedsubduction, of the Farallon and Aluk plates (Rapela et al. 1987, Pankhurst et al. 1999), to b) theinterruption of subduction, with the development of a Farallon-SAM transform margin and thedetachment of the Aluk plate (Aragón et al. 2011).The Paleogene magmatic record along the Andes suggests that it is segmented and episodic, with timegaps for magma emplacement, some episodes with a sense of continuous migration of the magmatic axiswith time (northern Chile and Peru), others with no sense of migration (northern and southern PatagonianBatholiths), reflecting major changes in subduction processes (Pankhurst et al. 1999). The Paleogenevolcanism along the Andes is also segmented and episodic, with unusual events of within-plate-likevolcanism such as in northern Chile (Cornejo and Matthews 2000) and Patagonia (Aragón et al. 2011).An ocean-continental plate transform system may be developed as a consequence of the relativetranslation of plates along the surface of a sphere. This geometry will develop where a segment of a plateboundary is perpendicular to the line from that segment to the pole of relative motion (Fig. 1A). Thisimplies that if the plate boundary is straight and long enough, it will be extensional at one end, continuingas a transform, and convergent at the other end, as the increased convergence angle causes the collapse ofthe transform into subduction (Fig. 1A). The critical angle in which the transform plate margin collapsesinto subduction could be >30o as can be observed in the Queen Charlotte transform system of the Pacific-North America plates (Fig 1B), also helped by a change in the coast line. It can also be observed fromFigure 1B that in the point of collapse from transform to subduction, the fore-arc is pushed into andbeneath the continental plate; the crust margin is duplicated in thickness and deformed into the Alaskanorocline. Furthermore, the complex Pacific-North America (NAM) Plates transform system (QueenCharlotte and San Andres) is a consequence of the Pacific-Farallon-NAM triple junction, and still hasremnants of the old Pacific-Farallon active ridge (not yet subducted) that preserve a microplate (Juan daFuca) and a continuous history of subduction.With this perspective of a complex continent-ocean plate transform system, an analogy can be made withthe Aluk-Farallon-SAM triple junction in the Paleogene (Fig. 1C). The Farallon-SAM reconstructions forthe 68-28 Ma interval (after Somoza and Ghidella 2005), shows that by that time, the Aluk-Farallon-SAMtriple junction had interacted with southern South America and that the Farallon plate had two episodes ofmoving with respect to SAM much currently to what occurs between the Pacific plate and northern NAM,with an Euler pole geometry as in Figure 1A, and with important strike-slip fault systems in southernPeru-northern Chile and Southern Chile, instead of central Chile (Santiago area), where a thrust and foldsystem prevails and batholiths of Paleogene age are present. In this scenario, the possibility remains thata few remnants of the Aluk-Farallon ridge could have remained un-subducted, preserving a hypotheticalmicroplate Tupac Amaru, and retaining subduction (through the Cenozoic) in the central Chile segment ofthe Andes.To the south of the Tupac Amaru microplate, the Patagonia-Farallon transform system was welldeveloped along the Proto-Liquiñe-Ofqui fault (Aragón et al., 2011), having a behaviour equivalent tothat of the San Andreas fault, with the transport and docking of peninsular Baja California in the westernUnited States. During this time, magmatic activity shows nearly total quiescence in the Patagonianbatholith, with volcanic activity having migrated to the fore- and back-arc (the Eocene convergencechange does not seem to interrupt the transform system, Figure 1C). To the north of the Tupac Amarumicroplate, a composite transform-obliquely convergent boundary, sliced by a system of strike-slip faults(Atacama and Domeyko fault systems) could have been developed during Paleogene, with an interruptionduring the Eocene compressive event with subduction. This structurally complex fault system shows uneven strain effects, with vertical and translational shifts of the component blocks and varying along thelength of the system and through time; having associated episodic calcalkaline and sporadic within-plate-like magmatism. The Peru batholith also shows episodic quiescence of magmatic activity for this time.Finally, as the Farallon-SAM convergence angle increases to the north (away from the Euler pole,Figs. 1A and 1C) the South American margin bends in an Orocline in the Eocene-Oligocene (McQuarrie2002). The good fit between the age of deformation of the Bolivian Orocline, and the increasedconvergence angle in the Farallon-SAM complex plate-transform-system at the orocline latitude cansustain an analogy with respect to the genesis of the Alaskan Orocline, implying that the BolivianOrocline could have developed where the continent-ocean plate transform system collapsed intosubduction and the fore-arc was pushed into and beneath the continental plate, duplicating the crustalthickness in that segment of continent margin.