The metamorphic architecture of the transpressional Gondwanide Orogen in southern South America: Insights from PTDt paths

ORIOLO, SEBASTIÁN; GONZÁLEZ, PABLO DIEGO; SCHULZ, B; GIACOSA, RAÚL; RENDA, EMILIANO; MARCOS, PAULO; SUÁREZ, RODRIGO

Cambridge

Congreso; Metamorphic Studies Group Research in Progress Meeting; 2021

The Mineralogical Society

The Gondwanide Orogeny represents a major late Palaeozoic tectonometamorphic event along southern Gondwana,roughly coeval with the Variscan collision recorded along the northern Gondwana margin. In South America it isnearly ubiquitous along the proto-Pacific margin, being intimately associated with protracted subduction. Most relicsof the Gondwanide Orogen were upper crustal rocks, but lower to middle crustal remnants are well-exposed inPatagonia (Argentina & Chile). Since robust P-T-D-t constraints are still scarce for the region, the aim of thiscontribution is to present a regional evaluation of integrated structural, petrological and petrochronological data, inorder to evaluate the spatial and temporal evolution at the orogeny scale.The orogen core comprises medium- to high-grade metamorphic complexes exposed between the North PatagonianAndes and the western North Patagonian Massif, recording dominantly high-T/high- to medium-P metamorphicconditions between the middle Carboniferous and the early Permian [1, 2, 3]. They are spatially associated withcoeval 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, yieldingcomparable high-T/high- to medium-P metamorphic conditions. In a similar way, these metamorphic rocks areintruded by middle to late Permian granitoids [e.g., 4]. Finally, Permian low- and very low-grade metamorphism isdocumented in the Ventania System to the northeast of the North Patagonian Massif as part of the Gondwanideforeland. Permian felsic magmatic rocks are also present, but mainly restricted to tuffs within the sedimentarysequence 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 shearzones. Deformation fabrics and kinematic data suggest a dextral-transpressive regional deformation regime. Themarked contrast between metamorphic conditions in northern Patagonia and the Ventania System seems to resultfrom different crustal-scale geodynamic controls. In Patagonia the pre-Gondwanide evolution was related toprotracted Palaeozoic subduction and basin evolution along an accretionary margin [7]. In contrast, in the VentaniaSystem there was reactivation of a crustal discontinuity between its Neoproterozoic basement and the adjacent Ríode la Plata Craton (RPC) [8]. In this context, widespread crustal thickening during the Gondwanide Orogeny innorthern Patagonia might have favoured stabilization of the Palaeozoic accretionary margin [1]. In contrast, the RPChad already attained a high thermal stability during Late Paleoproterozoic cratonization, thus resulting in a thicklithospheric mantle that behaved as a relatively rigid keel. Consequently, the RPC only recorded limited far-fieldGondwanide deformation and exhumation [9].