Thrust belts of the southern Central Andes: Along-strike variations in shortening, topography, crustal geometry, and denudation

GIAMBIAGI, L., MESCUA, J., BECHIS, F., TASSARA, A. Y HOKE, G

GEOLOGICAL SOCIETY OF AMERICA BULLETIN

GEOLOGICAL SOC AMER, INC

Lugar: Boulder; Año: 2012 vol. 124 p. 1339 - 1351

0016-7606

The Andean fold and thrust belts of west-central Argentina (33° and 36°S), above the normal subduction segment, present important along-strike variations in mean topographic uplift, structural elevation, amount and rate of shortening, and crustal root geometry. To analyze the controlling factors of these latitudinal changes, we compare these parameters and the chronology of deformation along eleven balanced crustal cross-sections across the thrust belts between 70° and 69°W, where the majority of the upper crustal deformation is concentrated, and reconstruct the Moho geometry along the transects. We propose two models of crustal deformation. A 33°40´S model, where the locus of upper-crustal shortening is aligned with respect to the maximum crustal thickness, and a 35°40´S model, where the upper-crustal shortening is uncoupled from the lower-crustal deformation and thickening. This degree of coupling between brittle upper crust and ductile lower crust deformation has strong influence on mean topographic elevation. In the northern sector of the study area, an initial thick and felsic crust favors the coupling model; while in the southern sector, a thin and mafic lower crust allows the uncoupling model. Our results indicate that interplate dynamics may control the overall pattern of tectonic shortening, however local variations in mean topographic elevation, deformation styles and crustal root geometry are not fully explained and are more likely to be due upper-plate lithospheric strength variations.