Contrasting tectonic controls in the last 6 Ma of retroarc volcanism in the transition zone from the Central to the Patagonian Andes (36- 42°S)

FOLGUERA, A.; GIANNI, G.; TOBAL, J.; SAGRIPANTI, L.; COLAVITTO, BRUNO; ORTS, D.L.; ROJAS VERA, E.

Potsdam

Conferencia; ILP?s Third Potsdam Conference; 2015

GFZ German Research Centre for Geosciences

Less than 6 Ma retroarc volcanism shows contrasting tectonic controls between 36 and 42°S. On one hand, in the northern sector, volcanism is associated with neotectonic contractional-transpressional structures that affect the Tromen volcanic plateau and the western Payenia volcanic plateau over the Malargüe fold and thrust belt. These contractional deformational belts are spatially linked to asthenospheric anomalies recently detected in magnetotelluric surveys (Burd et al., 2014), which suggests a probable linkage between a thermally debilitated lower crust and the sites of emplacement of retroarc products and shallow deformation. On the other hand south of 38°S, extensional troughs flanking the eastern Andean slope control arc and retroarc volcanism. These extensional structures are associated with crustal attenuated zones revealed from seismic and gravity data and with abnormally high thermal flows determined from magnetic data and previous seismic tomographies. These variations from retroarc volcanic fields associated with neotectonic compressional structures in the north to volcanism associated with extensional structures in the south can be explained by the strong tearing that the Nazca plate has suffered in the last 3-5 Ma visualized in seismic tomographies (Pesicek et al., 2012). These data show that south of 38°S, the subducted slab steepened in coincidence with the extensional structures that controlled volcanism at the eastern Andean slope in the last 5 Ma. Extensional deformation could be explained by the strong roll back that would have suffered the subducted slab in this sector produced by mantle flow ascending through the tearing at 38°S. Arc retraction described in previous proposals in the last 5-3 Ma is probably linked to this process.