Fábrica magnética y petrología del complejo volcánico-plutónico Huingancó, pérmico de la Cordillera del Viento, Andes neuquinos

Abstract

The Cordillera del Viento anticline is a structural high located in the northern part of the Neuquén Precordillera, formed during the Andean orogeny and whose core contains igneous and sedimentary rocks from previous orogenic cycles. The different diastrophic phases gave rise to a varied magmatic activity, deformation and first-order erosive unconformities represented in the stratigraphy of the area. Within this complex geological context, on the

western flank of the Cordillera del Viento, rocks of the Paleozoic basement were formed post- orogenically with respect to the Gondwanic cycle. These post-orogenic rocks are known as the

Huingancó Plutonic Volcanic Complex, which is integrated by a granodiorite facies, a monzogranite facies, ignimbrites of the La Premia Formation and subvolcanic rhyolitic domes, andesitic dikes and amphibole dacites. The plutons of the Huinganco Volcanic Plutonic Complex intrude the volcanites of the Arroyo del Torreón Formation and the sedimentites of the Huaraco Formation, both carboniferous and grouped within the Andacollo Group. In this work, a new U-Pb LA-ICP-MS dating was obtained in zircons of the granodiorites of the CVPH, which represents their age of crystallization and wich coincides with the previous ages available for this unit in the bibliography. With respect to the ASM fabrics of the Huingancó Plutonic Volcanic Complex plutons, the sites with high-temperature solid-state deformation are those that represent the original fabrics acquired during the emplacement of the plutons, since this deformation is associated with the cooling of the intrusives itself. The moderate and intense low-temperature solid-state deformations that slightly modified the magnetic fabric of the plutons of the granodiorites and monzogranites of the Huingancó Plutonic Volcanic Complex are attributed to the Andean orogeny. The space-generating mechanisms for the plutons were stoping and diking of amalgamated pulses. No ductile deformation was produced in the host rock. The hydrothermal alteration of the andesitic dikes of the late facies of the Huingancó Volcanic Plutonic Complex seems to be of Permian age, since the magnetic fabric of the dikes is normal, that is, the magnetic foliation is parallel to the dikes walls. The intrusives of the Huingancó Plutonic Volcanic Complex are calcalkaline granites from a subduction environment, due to the geochemical signature given by negative Nb and Ta anomalies, the positive Pb anomaly and enrichments in Cs, K, La and Rb. The Ba / La <20 ratio is compatible with an intraplate source. High Th / La ratios of around 0.6 are compatible with crustal contamination at the source of the magmas.The difference of more than 30 My between the granodiorites and the monzogranites of the Huingancó Plutonic Volcanic Complex suggests a facies evolution that did not occur at the site level but rather at the level of the magma source. First, the granodiorite facies was emplaced, which experienced mafic and felsic magma mingling and mixing at the source, as is evidenced by the presence of mafic microgranular enclaves. Then the remaining magma in the deepest magma chamber became more felsic and then rose and emplaced as the monzogranite facies around the granodiorite facies. The mafic magma injection process continued after the crystallization of the monzogranite facies evidenced by the intrusion of andesitic dikes of the late Huingancó Plutonic Volcanic Complex facies. A continuous subduction towards the end of the Gondwanic cycle seems to be the most suitable model for the tectonic environment of these rocks.