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

LAURA BEATRIZ GIAMBIAGI; JOSÉ FRANCISCO MESCUA; FLORENCIA BECHIS; ANDRÉS TASSARA; GREGORY HOKE

Antofagasta

Congreso; 13º Congreso Geológico Chileno; 2012

Universidad Católica del Norte, Sociedad 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 an initial thick and felsic model favors the uncoupling between lower and upper crustal deformation.