Neogene shortening contribution to crustal thickening in the back arc of the Central Andes

Abstract

To illustrate the Neogene shortening distribution in the back-arc units of the Central Andes and to estimate the contribution of the shortening to crustal thickening, two balanced crustal cross sections have been constructed across the northern and southern branches of the Bolivian orocline. Total Neogene shortening, which varies from 191 to 231 km, is accommodated by a crustal duplex below the Cordillera Oriental, but is insufficient to produce the 70 km of crustal thickness evidenced by geophysical data below the Altiplano. The best explanation for this anomalous thickening seems to be crustal underplating by material tectonically eroded from the continental margin; this process probably caused the Altiplano uplift. The subduction of oceanic lithosphere coupled with this underplating and a brief episode of gravity spreading of the Altiplano constituted the driving forces that produced Neogene shortening and development of the. ' Central Andes.

Andean structural control on interseismic coupling in the North Chile subduction zone

“…with the interplate rate during the interseismic period. Shortening in the Central Andes is mainly localized in the Subandean thrust-belt regions, according to geological and geodetic studies (Brooks et al, 2011;Chlieh et al, 2011;Baby et al, 1997;Kley and Monaldi, 1998;Bevis et al, 2001;Chlieh et al, 2004;Khazaradze and Klotz, 2003;Klotz et al, 1999;Norabuena et al, 1998). The magnitude of this shortening significantly varies (3 -15 mm/yr) depending on the study and we cannot resolve it with our data set (∼600 km away from the subandean region).…”

Thermal regime of fold and thrust belts—an application to the Bolivian sub Andean zone

“…The northern branch (15°to 18°S) is relatively narrow (50 to 100 km; Fig. 2) and shortening reaches 74 km (Baby et al, 1997). The southern branch (18°to 22°S) is rather wide (150 km) and shortening decreases from 140 km at 20°S to 86 km at 22°S (Baby et al, 1997).…”

“…For instance, in the Bolivian Andes, the current denudation rate of the intrusive bodies near La Paz is about 10 km in the last 10 Ma with a drastic acceleration in the most recent period (Benjamin et al, 1987;Masek et al, 1994), and evidence of current horizontal shortening in the Eastern Cordillera is very scarce or localized at the border. On the contrary, in the Sub Andean Zone (SAZ), horizontal shortening is about 10 km/Ma (Kley, 1996;Baby et al, 1997) or even faster during the last 10 Ma. Erosion is localized over anticlines with sedimentation in piggy-back basins.…”

“…2) and shortening reaches 74 km (Baby et al, 1997). The southern branch (18°to 22°S) is rather wide (150 km) and shortening decreases from 140 km at 20°S to 86 km at 22°S (Baby et al, 1997). The development of the Neogene foreland started at least during Late Oligocene times (27 Ma ago) when the deformation front migrated eastward from the current position of the Altiplano (Marshall and Sempere, 1991).…”

“…Dunn et al, 1995;Moretti et al, 1996;Baby et al, 1997;Kley et al, 1999;Colletta et al, 1999). To summarize, the SAZ is deformed by thin-skinned tectonics, with lateral variations being due to shortening amount, variable involved décollement levels and stratigraphic thickness.…”