Thrust-related metamorphism in Carboniferous slates of southern Patagonia (South America): the fate of forearc successions

SUÁREZ, RODRIGO JAVIER; GONZÁLEZ, PABLO DIEGO; ORIOLO, SEBASTIÁN; PARADA, MARTÍN NAZARENO; RAMOS, MIGUEL ESTEBAN; GHIGLIONE, MATÍAS C.; ZAFFARANA, CLAUDIA; ALBANO, JUAN; PONCE, JUAN JOSÉ

JOURNAL OF THE GEOLOGICAL SOCIETY

GEOLOGICAL SOC PUBL HOUSE

Año: 2024 vol. 181

0016-7649

The Devonian to early Carboniferous western margin of Patagonia (SouthAmerica) includes a NW-SE-trending magmatic arc associated with a palaeo NEdipping subduction zone. Along the Andean region of southern Patagonia, the EasternAndean Metamorphic Complex (EAMC) developed in a forearc position, consisting of asuccession of very low- to low-grade metaturbidite-metabasic rocks emplaced from theDevonian to Carboniferous periods. There are significant uncertainties surrounding thismetamorphic complex, mainly related to the tectonosedimentary setting of the basinand subsequent conditions of deformation and metamorphism, which hinder ourunderstanding of the orogenic architecture. To reveal the link between tectonics andmetamorphism, we conducted a structural analysis and sampled metapelites tomeasure illite crystallinity along a regional structural cross-section in the EAMC. Ouranalysis reveals broadly Lower to Upper Anchizonal metamorphism which is roughlysynchronous with deformation along northward-verging thrusts. These findings supportthe development of a forearc hyperextended basin that was subsequently closedduring the Gondwanide orogeny (late Paleozoic), a model that reconciles previousproposals suggesting passive margin vs. back-arc basin models. This closure led to theemplacement of suprasubduction zone ophiolites and turbidites over the continentthrough landward migration of brittle-ductile reverse shear zones.