Cretaceous orogeny, arc shifting and foreland dynamic subsidence linked to the Nalé flat-subduction event in Southern South America

GUIDO GIANNI; FEDERICO DÁVILA; ANDRES ECHAURREN; LUCAS FENNELL; JONATHAN TOBAL; CESAR NAVARRETE; PAULO QUEZADA; ANDRES FOLGUERA

Simposio; 8th International Symposium on Andean Geodynamics; 2019

We synthesize the Andean evolution between 35°30?S to 48°S intending to highlight early orogenicstages and to analyze their potential driving mechanisms. We review early tectonic stages of thedifferent fold-thrust belts that compose this Andean segment. Additionally, we examined thespatio-temporal magmatic arc evolution as a proxy of dynamic changes in subduction (Coney andReynolds, 1977). Contrary to previous hypothesis invoking several individual segments undergoingshallow subduction (e.g. Folguera and Ramos, 2011), we propose a hypothesis associated with theexistence of a continuous large-scale flat subduction setting in Cretaceous times. Notably, thisconfiguration may have had a similar size to the Peruvian Flat-slab, the present-largest flat-slab settingon earth (Gutscher et al., 2000). This process initiated diachronically in the late Early Cretaceousachieving its full development in Late Cretaceous to earliest Paleocene times, constructing a series offold-thrust belts from 35°30?S to 48°S. Furthermore, we assess major paleogeographic changes thattook place during flat-slab full development in Maastrichtian-Danian times. At this moment, an enigmaticAtlantic-derived marine flooding covered the Patagonian foreland reaching as far as the Andean foothills(del Río et al., 2014). Based on flexural and dynamic topography analyses, we suggest that focuseddynamic subsidence at the edge of the flat-slab may explain sudden marine ingression previously linkedto continental tilting and orogenic loading during a high sea level global stage.Folguera, A., Ramos, V.A., 2011. Repeated eastward shifts of arc magmatism in the Southern Andes: a revision to the long-term, pattern ofAndean uplift and magmatism. J. South Am. Earth Sci. doi:10.1016/j.jsames.2011.04.003.Coney, P,J., Reynolds, S.J., 1977. Cordilleran benioff zones. Nature, 270(5636), 403.del Río, C.J., Martínez, S.A., 2015. Paleobiogeography of the Danian molluscan assemblages of Patagonia (Argentina). Palaeog.Palaeoc. Palaeoec. 417, 274-292.Gutscher, M.A., Spakman, W., Bijwaard, H., Engdahl, E.R., 2000. Geodynamic of flat subduction: seismicity and tomographic constraintsfrom the Andean margin. Tectonics, 19, 814?833