Paleogene building of the Bolivian Orocline: Tectonic restoration of the central Andes in 2‐D map view

Abstract

Using available information on the magnitude and age of tectonic shortening, as well as paleomagnetically determined tectonic rotations, we have run a series of 2‐D map view restorations of the central Andes. Neogene shortening in the foreland belt induced only slight orogenic curvature of the central Andes. The constraints on the ages of the large observed fore‐arc rotations (average of 37° counterclockwise in southern Peru and 29° clockwise in northern Chile) indicate that the Bolivian Orocline formed during the Eocene‐Oligocene as a consequence of differential shortening focused in the Eastern Cordillera. To minimize local block rotations along the fore arc, the restoration that best fits the central Andean rotation pattern requires about 400 km of total (Paleogene plus Neogene) shortening near the Arica bend. This value corresponds to the upper bound of estimates of maximum horizontal shortening for the central Andes. Along‐strike variations in horizontal shortening in the back arc induced bending of the continental margin, block rotations with fore‐arc along‐strike extension, and/or orogen‐parallel transport of upper crustal material toward the symmetry axis of the orocline.

The Southern Central Andes vertical axis tectonic rotations: relations with the deformation pattern

“…Deformation in the Eastern Cordillera almost ceased between 12 and 8 Ma, with the formation of the San Juan de Oro surface and the initiation of the Subandean fold and thrust belt (Gubbels et al, 1993;Somoza et al, 2002;Somoza and Tomlinson, 2002a;Oncken et al, 2006). In coincidence with these observations, Arriagada et al (2008a) noted that Incaic deformation concentrated along the Chilean Precordillera and the Eastern Cordillera of southern Bolivia and northwestern Argentina. Deformation in the Chilean Precordillera began in the Late Cretaceous and peaked between ~45 and ~32 Ma, while shortening in the Eastern Cordillera occurred mainly in the Paleogene-Early Miocene, starting at ~45-40 Ma (Arriagada et al, 2008a).…”

“…Isacks (1988) presented a regional oroclinal model, suggesting that an ancient curvature of the margin was enhanced to accommodate along-strike gradient of Neogene horizontal-shortening in the eastern part of the Central Andes. However, Arriagada et al (2008a) ran a 2-D map view restoration experiment using first-order constraints on the magnitude and age of shortening and rotations in the Central Andes, and concluded that the Arica Deflection formed during the EoceneOligocene as a consequence of differential shortening focused in the Eastern Cordillera. According to these authors, Neogene shortening in the sub-Andean zone only slightly enhanced the orogenic curvature of the Central Andes.…”

3-D thermo-mechanical laboratory modeling of plate-tectonics: modeling scheme, technique and first experiments

“…The targeted situations include the deformation of the fore-arc, arc and back-arc along a seaward-concave plate boundary such as in the central Andes. The deformation near the symmetry axis is fundamentally three-dimensional with both trench-parallel and trenchperpendicular normal shortening (Kley, 1999;Hindle et al, 2002Hindle et al, , 2005Arriagada et al, 2008), and is most likely due to the stress conditions along the plate boundary. We have shown that we can estimate these stress conditions in our analogue models using simple cylindrical experiments.…”

“…For example, kinematic models of the Andes show that trenchparallel normal shortening as well as trench-perpendicular normal shortening existed in the center of the plate boundary curvature while the Andes were built (Kley, 1999;Hindle et al, 2002Hindle et al, , 2005Oncken et al, 2006;Arriagada et al, 2008;Gotberg et al, 2009). Two-dimensional, numerical simulations reveal that trench-parallel compression is produced near the symmetry axis of a seaward-concave plate boundary if interplate friction is high and/or the subducting lithosphere has a low flexural rigidity (Boutelier and Oncken, 2010).…”

The Lautaro Basin: A record of inversion tectonics in northern Chile

“…In the other hand, the Paleogene deformation is more widely distributed across the Andes of northern Chile (Arriagada et al, 2000(Arriagada et al, , 2003(Arriagada et al, , 2006bTaylor et al, 2007). Eocene-Oligocene deformation was accompanied by tectonic shortening, mountain uplift and significant clockwise block rota tions (e.g., Hartley et al, 1992;Riley et al, 1993;Forsythe and Chisholm, 1994;Randall et al, 1996;Taylor et al, 1998;Arriagada et al, 2000;Somoza and Tomlinson, 2002;Arriagada et al, 2003Arriagada et al, , 2006bArriagada et al, , 2008. Fission track thermochronology indicates that tectonic uplift and erosion were mainly active during the EoceneEarly Oligocene 'Incaic Orogeny', when at least 4-5 km of rocks were eroded during exhumation of tectonic blocks of the Cordillera de Domeyko between ca.…”