Neogene growth of the North Patagonian Andes

FOLGUERA, ANDRES; ENCINAS, A.; ALVAREZ PONTORIERO, O.; ORTS, D.; GIANNI, GUIDO; ECHAURREN, A.; LITVACK, V.; NAVARRETE, C.; SELLÉS DANIEL; TOBAL, JONATHAN; RAMOS, MIGUEL; FENNELL, LUCAS; FERNANDEZ, LUCÍA; GIMENEZ, MARIO E; MARTINEZ, M PATRICIA; RUIZ, F.; IANNELLI, SOFÍA

The evolution of the Chilean-Argentinean Andes

Springer International Publishing

Año: 2016; p. 485 - 510

After a Late Cretaceous to Paleocene stage of mountain building, the North Patagonian Andes were extensionally reactivated leading to a period of crustal attenuation. The result was the marine Traiguén Basin characterized by a quasi-oceanic basement floor that spread between 27 and 22 Ma and closed by 20 Ma, age of postdeformational granites that cut the deformed basin infill. As a result of basin closure, accretion of the Early Triassic metamorphic Chonos Archipielago took place against the Chilean margin, emplacing a stripe of high density (mafic) rocks on the upper crust, traced with gravity data through the Chonos Archipiélago. After this, contractional deformation had a rapid propagation between 21-18 and 14.8 Ma reestructuring the Patagonian Andes and producing a wide broken foreland zone. This rapid advance of the deformational front registered from synorogenic sedimentation was accompanied at the latitudes of North Patagonia by an expansion of the arc magmatism between 19 and 14 Ma, suggesting a change in the subduction geometry at that time. After this, a sudden retraction of the contractional activity took place around 13.5-11.3 Ma, accompanied by a retraction of magmatism and an extensional reactivation of the Andean zone that controlled retroarc volcanism up to 7.3-(4.6) Ma. This particular evolution is explained by a shallow subduction regime in the northernmost Patagonian Andes, probably facilitated by the presence of the North Patagonian massif lithospheric anchor that would have blocked drag basal forces creating low pressure conditions for slab shallowing. Contrastingly, to the south, the accretion of the Chonos Archipielago explains rapid propagation of the deformation across the retroarc zone. These processes occurred at the time of rather orthogonal convergence between Nazca and South American plates after a long period of high obliqueness. Crustal and accretionary prism removal during forearc tectonic erosion and recycling of crustal crust from the foreland zone facilitated during shallow subduction and Chonos crustal accretion changed the composition of arc volcanism forming hybrids of mantle derived and crustal recycled products in ignimbritic facies on a barely thickened crust. Finally, convergence deceleration in the last 10 My could have led to extensional relaxation of the orogen probably enhanced by supercritical conditions of the orogenic wedge of the Northern Patagonian Andes.