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

ORIOLO S.; GONZÁLEZ, P. D.; SCHULZ, B.; GIACOSA, R. ; RENDA E.M.; MARCOS, P.; SUAREZ, R.; BALLIVIÁN JUSTINIANO; CHRISTIANSEN, R.; YOYA, B.; RESTELLI, F.; BASEI, M.

Cambridge

Congreso; Metamorphic Studies Group 40th Anniversary Meeting; 2021

The orogen core comprises medium- to high-grade metamorphic complexes exposed between the North Patagonian Andes and the western North Patagonian Massif, recording dominantly high-T/high- to medium-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 highgrade metamorphism is documented by the middle to late Permian in the eastern North Patagonian Massif, yielding comparable high-T/high- to medium-P metamorphic conditions. In a similar way, these metamorphic rocks are intruded by middle to late Permian granitoids [e.g., 4]. Finally, Permian low- and very low-grade metamorphism is documented in the Ventania System to the northeast of the North Patagonian Massif as part of the Gondwanide foreland. Permian felsic magmatic rocks are also present, but mainly restricted to tuffs within the sedimentary sequence and a small syenitic-granitic intrusion. In all these areas the Gondwanide Orogen is dominated by WNWESE- to NNW-SSE-striking fabrics, mainly associated with a regional metamorphic foliation and, locally, late shear zones. Deformation fabrics and kinematic data suggest a dextral-transpressive regional deformation regime. The marked contrast between metamorphic conditions in northern Patagonia and the Ventania System seems to result from different crustal-scale geodynamic controls. In Patagonia the pre-Gondwanide evolution was related to protracted Palaeozoic subduction and basin evolution along an accretionary margin [7]. In contrast, in the Ventania System there was reactivation of a crustal discontinuity between its Neoproterozoic basement and the adjacent Río de la Plata Craton (RPC) [8]. In this context, widespread crustal thickening during the Gondwanide Orogeny in northern Patagonia might have favoured stabilization of the Palaeozoic accretionary margin [1]. In contrast, the RPC had already attained a high thermal stability during Late Paleoproterozoic cratonization, thus resulting in a thick lithospheric mantle that behaved as a relatively rigid keel. Consequently, the RPC only recorded limited far-field Gondwanide deformation and exhumation [9]