Petrography, magnetic fabrics and timing of emplacement in relation to the San Rafael Orogenic Phase of the Huingancó Granitoids, Permo-Triassic of the Cordillera del Viento, Argentina

Abstract

This work presents a petrographic and anisotropy of magnetic susceptibility (AMS) study of the Huingancó Volcanic-Plutonic Complex, a suite of granitoids (granodiorites and monzogranites) and minor volcanic rocks that crop out in the Cordillera del Viento, which is located in the Southern Central Andes, Neuquén Province, Argentina. The granodiorites have an Early Permian crystallization age (U-Pb ages of 283 ± 1 Ma and 282 ± 2 Ma), whereas the monzogranites are of Late Permian age (U-Pb age of 258 ± 9 Ma) and belong to the Choiyoi Magmatic Province, which developed before the Andean subduction. Plutons and dikes, metasedimentary host rocks, and the younger volcanic units were studied with the AMS technique to characterize their internal structure, which was integrated with the regional structural framework. The petrographic study revealed that the original magmatic fabrics of the granodiorites and monzogranites of the Huingancó Complex were overprinted by solid-state deformation of varying intensity. However, the magnetic ellipsoids are clearly defined, so we interpret that the magnetic fabrics of the Huingancó Granitoids developed contemporaneously with the emplacement of the granitoids. The magnetic fabrics of the granodiorites are sub-parallel to the NW-SE-oriented and SW-vergent subvertical structures generated by the San Rafael Orogenic Phase in the Cordillera del Viento area. In turn, the magnetic fabrics of the monzogranites are parallel to the contact with the host rocks and farther from the contacts, they become more dispersed, suggesting that they represent magmatic flow fabrics during pluton emplacement. The emplacement of the granodiorites is interpreted as syn-tectonic with respect to the San Rafael Orogenic Phase, whereas the monzogranites are interpreted to have emplaced post-tectonically, ~25 Myr after, in shallower tectonic conditions. The structural study of the Huingancó Granitoids provided insight into the Late Paleozoic deformation in this area, both during and after the San Rafael Orogenic Phase, marking a transition of the magmatism within the Choiyoi Province. Our results exemplify granitoids affected by contrasting tectonic settings, likely reflecting the transition from a compressional regime associated with the final stages of the amalgamation of the Gondwana supercontinent to an extensional regime related to its subsequent break-up.