Emplacement and temporal constraints of the Gondwanan intrusive complexes of northern Patagonia: La Esperanza plutono-volcanic case

Two main lines of evidence disagree whether or not the Patagonian blocks collided with Gondwana. All models invoke the voluminous magmatism of the La Esperanza Complex as evidence for active subduction magmatic arc or to a postcollisional setting. The evolution of this bimodal igneous suite is reassessed with field, geochronological (SHRIMP U-Pb zircon and K-Ar mica) and petrophysical data. Emplacement of high-K calk-alkaline granitic magmas occurred at shallow crustal levels (2–8±2km depth) related to the development and collapse of a caldera associated with a regional NW-SE structural trend. Magmatism involved intermediate hybrid pulses at 273±2Ma and 255±2Ma (Prieto Granodiorite) that shifted like a yo-yo to acidic magmas at 260±2Ma and 250±2Ma (Donosa and Calvo granites). Absence of solid-state deformation features and the low anisotropy degrees in the granites indicate that its fabric is magmatic in origin. Magnetic fabric in granodiorites displays a concentrical pattern with subhorizontal foliations and lineations. Parallel to the volcanic axis, magnetic foliations and moderately plunging lineations indicate a common feeder system for plutonics and volcanics. Donosa Granite shows a discordant pattern with WNW-ESE ENE-WSW trending low plunging lineations and foliations. The plutono-volcanic system construction (273–255Ma) followed NW-SE and NE-SW diamond shape faults trends and supracrustal discontinuities. Magmatic Climax is bracketed at 260Ma. The collapse of the edifice is evidenced by the intrusion of acid magma plugs and dike swarms between 250 and 246Ma. A similar age range was identified in other areas of Patagonia related to syn and postcollisional tectonic events. No evidence of tectonic activity such as major uplift, metamorphism or thrusting was found excepting regional strike-slip faulting and extension. Therefore, La Esperanza Complex is a high crustal level episode, and as such may not have structurally recorded an active collision during its crystallization and cooling. [Display omitted] •La Esperanza Plutono-volcanic Complex shows a protracted subvolcanic magmatic activity between 273 and 245Ma.•Volcanic activity is bracketed between ca 265 and 245Ma.•AMS and microstructures indicate that the fabrics were acquired in the magmatic state with no overimposed deformation.•A change in far field structural control is recorded at ca ~260Ma, contemporaneously with magmatic climax.•Collapse of the magmatic edifice might have occurred between 25