Relationship between tectonic shortening, topographic elevation, crustal geometry and denudation in the Southern Central Andes, 33°-36°S

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

Antofagasta

Congreso; XIII Congreso Geológico Chileno; 2012

Asociación Geológica de Chile

The Andean fold and thrust belts between 33° and 36°S present important along-strike variations in mean topographic uplift, structural elevation, amount and rate of shortening, and crustal thickness. 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 and reconstruct the Moho geometry. Our results indicate a synchronous onset of deformation along-strike at ca. 17-18 Ma, a progressive southward reduction of total amount of shortening from 55 to 10 km, shortening rates from 3.8 to 0.7 mm/a, and  a small reduction in crustal thickness from 51 to 47 km. However, average topographic elevation does not vary  gradually southward as the other parameters, with an abrupt step from 3,500 to 2,200 m close to 35°S. We  propose two models of crustal deformation. A 33°40´S model, with an initial thick and felsic crust that favors the coupling between brittle upper crust and ductile lower crust deformation, and a 35°40´S model, where thinner and more mafic lower crust due to the opening of the Mesozoic rift basin favors the uncoupling thinner and more mafic lower crust due to the opening of the Mesozoic rift basin favors the uncoupling between lower and upper crustal deformation.