Structure and metamorphism of the Gondwanan basement in the Bariloche region (North Patagonian Argentine Andes)
In the Bariloche region, the Gondwanan basement consists of metamorphic and deformed igneous rocks intruded by Mesozoic and Tertiary granitoids. Metasediments and amphibolites have been affected by three main deformation events (D1, D2 and D3). D1 (S1 foliation) is well shown preserved in the microlithons of the S2 regional foliation and in albite and garnet porphyroblasts. Both foliations have been folded by upright open folds with associated crenulation (S3) locally developed in the D3 folds hinge zones. An early-stage (syn-D1) subduction episode can be invoked based on evidence of high pressure (HP) metamorphism in schists and amphibolites as well as on the presence of pre-collisional I-type granitoids. D2–D3 developed under regional intermediate pressure–low pressure (IP–LP) metamorphic conditions. High temperature (HT) conditions were reached, as deduced from regional migmatization and the intrusion of syn- to late-orogenic S-type granitoids. The transition from HP to IP metamorphic conditions could be associated with the emplacement of NE directed crustal-scale thrusts during D2.