The metamorphic architecture of the transpressional Gondwanide Orogen in Patagonia (southern South America): Insights from P-T-D-t paths

ORIOLO, SEBASTIAN; GONZALES, PABLO; SCHULZ; GIACOSA, RAUL; RENDA, EMILIANO; MARCOS, P; SUAREZ, R; BALLIVIÁN JUSTINIANO, C; CHRISTIANSEN, R; YOYA, MARIA BELEN; RESTELLI, FLORENCIA; BASEI, MIGUEL

Encuentro; MSG; 2021

The Gondwanide Orogeny represents a major Late Paleozoic tectonometamorphic event alongsouthern Gondwana, being roughly coeval with the Variscan collision recorded along the northernGondwana margin. In the particular case of South America, it is nearly ubiquitous along the proto-Pacific margin, being intimately associated with protracted subduction. Most relics of theGondwanide Orogen correspond to upper crustal rocks, whereas lower to middle crustal remnantsare particularly well-exposed in Patagonia (Argentina & Chile). Since robust P-T-D-t constraints arestill scarce for the region, the aim of this contribution is to present a regional evaluation of integratedstructural, petrological and petrochronological data, in order to evaluate the spatial and temporalevolution at the orogeny scale.The orogen core is related to medium- to high-grade metamorphic rocks exposed between the NorthPatagonian Andes and the western North Patagonian Massif, recording dominantly high-T/high- tomedium-P metamorphic conditions between the Middle Carboniferous and the Early Permian [1, 2,3]. They are spatially associated with coeval calc-alkaline granitoids with continental arc affinity [4, 5,6].Further northeast, regional medium- to high-grade metamorphism is documented by the Middle toLate Permian in the eastern North Patagonian Massif, yielding comparable high-T/high- to medium-Pmetamorphic conditions. In a similar way, these metamorphic rocks are intruded by Middle to LatePermian granitoids [e.g., 4].Finally, Permian low- and very low-grade metamorphism is also documented in the Ventania System,located to the northeast of the North Patagonian Massif as part of the Gondwanide foreland.Permian felsic magmatism is also present, but mainly restricted to tuffs interlayered within thesedimentary sequence.In all aforementioned areas, the Gondwanide Orogen is dominated by WNW-ESE- to NNW-SSE-striking fabrics, mainly associated with a regional metamorphic foliation and, locally, with late shearzones. According to deformation fabrics and kinematic data, the regional deformation regime mighthave been associated with dextral transpression.The marked contrast between northern Patagonia, from the North Patagonian Andes to the NorthPatagonian Massif, and the Ventania System in terms of metamorphic conditions seem to result fromdifferent crustal-scale geodynamic controls. In the case of Patagonia, the pre-Gondwanide evolutionwas related to protracted Paleozoic subduction and basin evolution along an accretionary margin [7].In contrast, regional metamorphism and deformation in the Ventania System resulted from thereactivation of a crustal discontinuity between its Neoproterozoic basement and the adjacent Río dela Plata Craton [8]. In this context, widespread crustal thickening during the Gondwanide Orogeny innorthern Patagonia might have favoured a relative stabilization of the Paleozoic accretionary margin[1]. In contrast, the Río de la Plata Craton already attained a high thermal stability already during LatePaleoproterozoic cratonization, thus resulting in the presence of a thick lithospheric mantle, which inturn behaved as a relatively rigid keel that prevented migration of Gondwanide deformation furtherinland. Consequently, the Río de la Plata Craton only recorded limited far-field Gondwanideprocesses [9].