The role of the upper plate in the Andean orogeny: insights from field observations to numerical modeling

BARRIONUEVO, M., LIU, S., MESCUA, J. QUINTEROS, J., BABEYKO, A., GIAMBIAGI, L., SOBOLEV, S.

Congreso; XV Congreso Geológico Chileno; 2018

The Southern Central Andes shows a pronounced latitudinal variation in the structural pattern with a decrease in shortening and orogenic width from 30º S to 36º S. One of the most important factors invoked is the variation in subduction dynamics with a zone of flat-slab subduction from 27º S to 33º S and a normal subduction setting to the south. Despite this main control, there are other factors which can control deformation, such as the strength of the upper plate. This have been proposed previously for this zone as well for the Altiplano-Puna region. Whilst in the plateau region it was tested with numerical modeling, in the 30-36ºS region it has been not.Based on field geological observations and geophysical data along the 36º S transect we have constructed a conceptual model which reflects the current day structure of the orogen. In this zone the Malargüe fold-and-thrust belt developed under Andean contraction as a thick-skinned belt. Here the deformation is accommodated by the interaction between reactivated pre-andean faults related to the Upper Triassic-Lower Jurassic rifting in the Neuquén basin and newly created reverse faults. This rifting phase could have produced a different configuration of the upper plate due to thinning of the crust which increases the strength of the overall lithosphere leading to an uncoupling of the deformation in the upper and lower crust. Besides this interrogation we want to address the questions regarding the location and vergency of the main detachment and if its activation and deactivation responds to the balance of the tectonic driving forces vs gravitational forces.By means of large scale finite element numerical modeling we aim to evaluate the influence of the upper plate during the Andean deformation. For this we prescribed the slab subducting geometry and kinematics and focused only in the upper plate characteristics. With this setup, the slab transmit stress to the upper plate and we get a realistic temperature distribution. With different compositions and geometries of the South American plate we try to address the controls of this plate in the deformation.Afterwards we would evaluate the development of thin vs thick-skinned belts with a high resolution model of the upper plate with no subduction but focused in upper crust deformation.