Neogene growth of the Patagonian Andes

FOLGUERA, ANDRÉS; GIANNI, GUIDO M.; ENCINAS, ALFONSO; ÁLVAREZ, ORLANDO; ORTS, DARÍO; ECHAURREN, ANDRÉS; LITVAK, VANESA D.; NAVARRETE, CÉSAR; SELLÉS, DANIEL; TOBAL, JONATHAN; RAMOS, MIGUEL E.; FENNELL, LUCAS; FERNÁNDEZ PAZ, LUCÍA; GIMÉNEZ, MARIO; MARTÍNEZ, PATRICIA; RUIZ, FRANCISCO; IANELLI, SOFÍA

The evolution of the Chilean-Argentinean Andes

Springer International Publishing

Lugar: Berlin; Año: 2018; p. 475 - 501

After a Late Cretaceous to Paleocene stage of mountain building, the NorthPatagonian Andes were extensionally reactivated leading to a period of crustalattenuation. The result was the marine Traiguén Basin characterized by submarinevolcanism and deep-marine sedimentation over a quasi-oceanic basement floor thatspread between 27 and 22 Ma and closed by 20 Ma, age of syndeformational granitoids that cut the basin infill. As a result of basin closure, accretion of the UpperTriassic metamorphic Chonos Archipelago took place against the Chilean margin, overthrusting a stripe of high-density (mafic) rocks on the upper crust, traced bygravity data through the Chonos Archipiélago. After this, contractional deformationhad a rapid propagation between 19 and 14.8 Ma rebuilding the Patagonian Andesand producing a wide broken foreland zone. This rapid advance of the deformationalfront, registered in synorogenic sedimentation, was accompanied at the latitudes of theNorth Patagonian Andes by an expansion of the arc magmatism between 19 and14 Ma, suggesting a change in the subduction geometry at that time. Then a suddenretraction of the contractional activity took place around 13.5?11.3 Ma, accompaniedby a retraction of magmatism and an extensional reactivation of the Andean zone thatcontrolled retroarc volcanism up to 7.3?(4.6?) Ma. This particular evolution isexplained by a shallow subduction regime in the northernmost Patagonian Andes,probably facilitated by the presence of the North Patagonian massif lithosphericanchor that would have blocked drag basal forces creating low-pressure conditions forslab shallowing. Contrastingly, to the south, the accretion of the Chonos Archipelagoexplains rapid propagation of the deformation across the retroarc zone. These processes occurred at the time of rather orthogonal to the margin convergence betweenNazca and South American plates after a long period of high oblique convergence.Finally, convergence deceleration in the last 10 My could have led to extensionalrelaxation of the orogen.