Nazca–South America interactions and the late Eocene–late Oligocene flat‐slab episode in the central Andes

Abstract

The most prominent features of the Andean range are the Altiplano and Puna plateaus, which were constructed by crustal shortening and uplift over the past ∼45 Myr. The early construction of these plateaus may have controlled subsequent growth of the orogen. Proposed models have suggested that an abrupt acceleration in relative motion between the Nazca plate and the South American plate at ∼30 Ma may have led to compression of the continent. However, the major plate motion change occurred at 25–23 Ma, and paleomagnetic rotations and crustal shortening of the Andean forearc require that the Arica Bend formed prior to about 25 Ma. Inferred history of flat‐slab subduction along the Altiplano section of the Andean margin and the structure of the adjacent South American cratonic shield combine to suggest an alternate scenario, based partly upon geodynamic models of oceanic‐continental plate interactions in subduction zones. We propose that central Andean tectonism may have been controlled by two distinct regimes of subduction: (1) oblique subduction along the central Andean margin during the late Eocene and Oligocene accompanied by downdip alignment with the center of the Amazonian Shield (flat‐slab activity in this phase of orogenesis may have been caused by a combination of cratonic root enhanced tectonics and oceanic plateau subduction) and (2) an abrupt transition to trench‐normal subduction after ∼25 Ma toward the more distal São Francisco Craton was accompanied by a return to normal angle subduction. Similar interactions are hypothesized to have occurred during the Laramide Orogeny in western North America.

Flat slab deformation caused by interplate suction force

“…[]. The shield appears to be absent from the upper mantle structure beneath the Eastern Cordillera because the mantle of the Brazilian Shield lithosphere is likely to have been largely removed in this region by the slab [ O ' Driscoll et al ., ]. The mantle beneath the sub‐Andean shows a high‐velocity zone, which we interpret as the shield lithosphere.…”

“…This process is much easier with a thick crust and nearby lithospheric root, which obstructs the inflow, and hence enhances the suction force as suggested in O ' Driscoll et al . [].…”

“…Therefore, other factors such as the enhanced mantle wedge suction by a thick continental craton near the subduction zone are also suggested to be significant in flattening the slab in South America [ Manea et al ., ; O ' Driscoll et al ., ]. The change in distance to the cratonic root, which controls the interplate suction force, is suggested to have caused the flatten and resteepen of the Oligocene flat slab beneath the Altiplano [ O ' Driscoll et al ., ].…”

Tectonic Regimes of the Central and Southern Andes: Responses to Variations in Plate Coupling During Subduction

“…In terms of plate velocity, many factors have been emphasized in the assessment of large‐scale variations in plate motion, including the rates of relative convergence, trench retreat (retrograde motion of the subduction hinge), and absolute trenchward advance of the overriding South American Plate (Maloney et al, ; Pilger, ; Pardo‐Casas & Molnar, ; Schellart, ; Silver et al, ; Somoza & Zaffarana, ; Sobolev & Babeyko, ; Vietor & Echtler, ), as well as changes in the direction or obliquity of convergence (O'Driscoll et al, ; Scheuber et al, ; Somoza, ).…”

Physiographic and tectonic settings of high-sulfidation epithermal gold–silver deposits of the Andes and their controls on mineralizing processes

“…These deposits occur near the Domeyko fault system of the Chilean Precordillera, which also contains the behemothian Escondida, Chuquicamata, and Collahuasi porphyry Cu districts. All of these deposits were emplaced during, or immediately after the late Eocene Incaic orogenic event which has been ascribed to an inferred episode of slab flattening, crustal thickening, volcanic lull and subsequent eastward shift of the volcanic arc (Mpodozis and Cornejo, 2012;O'Driscoll et al, 2012).…”