The influence of lithospheric geometry in Andean evolution: an example from the 33-36°S area

BARRIONUEVO, M.; LIU, SIBIAO; MESCUA, JOSÉ F.; YAGUPSKY, DANIEL; QUINTEROS, JAVIER; GIAMBIAGI, LAURA B.; SOBOLEV, STEPHAN; RODRIGUEZ PICEDA, CONSTANZA; STRECKER, MANFRED R.

Sicilia

Congreso; 3rd YORSGET Young Researchers in Structural Geology and Tectonics.; 2022

Universita di Catania; University of Aberdeen

A current topic of debate in the Southern Andean tectonics is regarding the vergence of the orogenic system,with two end-member models: an east-vergent model and a west-vergent model. The former proposes that themain detachments that accommodate shortening are rooted below the orogen at 10-12 km depth and thedifferent morphotectonic units have been successively uplifted from west to east (Ramos et al., 2004; Fariaset al., 2010; Giambiagi et al., 2012). In turn, the west-vergent model interprets that the deformation isaccommodated by an east-dipping shear zone rooted in the lower crust beneath the eastern flank of the Andes(Armijo et al., 2010; Riesner et al., 2018, 2019). Furthermore, these models estimate different amount ofshortening. At the Aconcagua transect at ~34°S, for example, there is around 70 km shortening calculated inthe east-vergent model (Farias et al., 2010; Giambiagi et al., 2012) while 30-50 km are estimated in the westvergentmodel (Riesner et al., 2018).We develop geodynamical models representative of two E-W-transects (33°40´S and 36°S) based ongeological and geophysical information about the area. We try to replicate the geometry of the upper plate,with an asymmetric lithosphere-asthenosphere boundary due to subduction corner flow. We split the modeldomain to west and east parts, where the western part has a thicker lithosphere representing the forearc as arigid indenter (Farías et al., 2010) than the eastern part in which the lithospheric mantle is eroded thermally bythe corner flow.Results of our models show that the geometry of the lithosphere-asthenosphere boundary is an importantfactor controlling the orogenic vergence. In particular, a principal east-vergent crustal-scale detachment isformed in both transects, which is in accordance with the east-vergent model (e.g. Ramos et al., 2004; Fariaset al., 2010; Giambiagi et al., 2012).