The origin of Patagonia: insights from Permian to Middle Triassic magmatism of the North Patagonian Massif

Abstract

We conducted a U–Pb–Hf isotope study on zircon crystals from ignimbrites of the Changhsingian to Olenekian (253–248 Ma) Los Menucos Basin in the North Patagonian Massif (NPM), Argentina, in order to evaluate the age and petrogenesis of the magmas. Additionally, a compilation of whole-rock geochemistry and U–Pb–Hf in zircon isotope data for the Permian to Middle Triassic rocks of the NPM, for comparison with our data, was made to assess whether Patagonia would have been an exotic terrane accreted to SW Gondwana during the late Palaeozoic. We interpret the available U–Pb–Hf data to suggest that northern Patagonia experienced eastward arc expansion from the early Permian, about 273 Ma ago. This ∼820 km arc expansion event involved crustal shortening and magmatism with high-silica adakitic affinity, resulting in Hf-isotopic pull-down. At 253 Ma, slab steepening became associated with the coeval emplacement of ignimbrites of the Los Menucos Basin, which involved post-orogenic to intraplate magmatism. During the Middle Triassic, a slab break-off triggered uplift and basaltic underplating, promoting the emplacement of dike swarms with C-type adakitic signature at 246–244 Ma. The Hf isotope data for SW Gondwana for the same period indicate distinct trends that are explained here by differential slab roll-back since the Guadalupian, in a slab-tearing setting. Therefore, Permian to Middle Triassic magmatism is interpreted as having been associated with an eastward-directed proto-Pacific subduction system, which ultimately supports an autochthonous origin for Patagonia.

Palaeozoic – Early Mesozoic geological history of the Antarctic Peninsula and correlations with Patagonia: Kinematic reconstructions of the proto-Pacific margin of Gondwana

“…A para-autochthonous model is preferred here (Fig. 11), in broad agreement with the recent model presented by Falco et al (2022) based on Lu -Hf isotope geochemistry, for the development of the Permian continental margin, with deformation and magmatism associated with slab dynamics and slab loss. Crustal block translation (e.g.…”

“…These values overlap with the mean values reported from the Permian accretionary complexes of the northern Antarctic Peninsula and west Patagonia investigated by Fanning et al (2011) and Castillo et al (2016). They reported similar ranges in εHf (− 15 to +4), but with a concentration in the range − 5 to − 1, which in turn overlaps with reported εHf values of the Choiyoi volcanic provinces (Castillo et al, 2016;Falco et al, 2022).…”

“…autochthonous (e.g. Martínez Dopico et al, 2021;Falco et al, 2022;Gregori et al, 2016;Kostadinoff et al, 2005;Rapalini et al, 2013), and allochthonous (e.g. Pankhurst et al, 2006;Ramos, 2008;Bahlburg, 2021) models proposed.…”

“…Primary volcanic successions crop out in central Patagonia (e.g. Gianni and Navarrete, 2022;Falco et al, 2022) and subvolcanic equivalents are preserved across large parts of Patagonia, into Tierra del Fuego and sectors of the Antarctic Peninsula (eastern Graham Land and western Palmer Land; Fig. 11).…”

Devonian to Early Carboniferous Retreating—Advancing Subduction Switch in the Northwestern Patagonia Accretionary Orogen: U‐Pb and Lu‐Hf Isotopic Insights

“…Although the development and subsequent accretion of the Chaitenia island-arc (Hervé et al, 2016;Rapela et al, 2021;Figure 1a) may represent the Devonian to early-Carboniferous geodynamic evolution, our results and analysis indicate that changes from extensional to contractional regime could be explained by steepness variations of the subducted slab (Figure 7). This model is closely related to recent geodynamic reconstruction for the late Paleozoic (e.g., Falco et al, 2022;Marcos et al, 2020;Oriolo et al, 2019Oriolo et al, , 2023. In this configuration, the presence of contemporaneous, paired metamorphic belts, with high-pressure metamorphism prevailing in the forearc and regional high-temperature metamorphism developing in the arc and back-arc region, documents the typical metamorphic architecture of an accretionary orogen (Brown, 2006(Brown, , 2009.…”