The metamorphic rocks of the Nunatak Viedma in the Southern Patagonian Andes: Provenance sources and implications for the early Mesozoic Patagonia-Antarctic Peninsula connection

Abstract

The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based on its geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphic nature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pb dating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognized very-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, and scarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yielded prominent age population peaks at ~1090, ~960, ~630, ~520, ~480-460, ~380, ~290-260, ~235-225 Ma that are typical of Gondwanide affinity, and youngest grains at ~208 Ma. Maximum depositional ages of 225, 223 and 212 Ma were calculated for each sample from the youngest cluster of ages. This distinctive and novelty Late Triassic age justifies differentiate the Nunatak Viedma Unit from the Devonian-early Carboniferous and Permian-Early Triassic (?) belts of the Eastern Andean Metamorphic Complex. Possible primary source areas for the detrital zircons are outcropping in southern Patagonia, the Antarctic Peninsula, and the Malvinas Islands. Additionally, secondary sources could be part of the erosion and recycling of metasediments from the Eastern Andean Metamorphic Complex. We propose that the cluster of Triassic ages is related to the volcanic arc emplaced along the Antarctic Peninsula and active at that timewhen was still attached to southern Patagonia during the Triassic. The dynamics of the early Mesozoic orogen is also discussed.

The Late Triassic Ischigualasto Formation at Cerro Las Lajas (La Rioja, Argentina): fossil tetrapods, high-resolution chronostratigraphy, and faunal correlations

“…The reasons behind this pattern are not clear. Pyroclastic deposits, such as bentonites, ignimbrites, and welded tuffs, indicate a high volcanic influence in the area and elsewhere 87 – 90 . These materials are much more abundant in the upper third of the studied succession, reaching significant thicknesses in certain intervals.…”

The low-grade basement at Península La Carmela, Chilean Patagonia: new data for unraveling the pre-Permian basin nature of the Eastern Andean Metamorphic Complex

“…Outcrops at Lago O´Higgins-San Martin show main peaks of Neoproterozoic and Mesoproterozoic ages, with subordinate Archean components, and isolated Paleozoic grains (Fig. 8B-G; Hervé et al 2003;Augustsson et al 2006;Moreira et al 2013;Permuy-Vidal et al 2014;Malkowski et al 2016;Suárez et al 2019a). However, it turns out to be different to rocks from the Cerro Negro Schists, located in the western Deseado Massif that exhibits scarce Proterozoic zircons (Fig.…”

“…The youngest metasedimentary units of the EAMC were deposited during the Permian and Triassic times and sourced from a magmatic arc and continental basement rocks (Augustsson and Bahlburg 2008). In this context, the late Paleozoic to early Triassic reorganization of crustal blocks of the south-western margin of Gondwana would have caused the westward migration of the magmatic arc because of the accretion/collision of the Antarctic Peninsula against the Gondwana margin (Calderón et al 2016;Suárez et al 2019a, b;Rojo et al 2021). The Permian-Lower Triassic igneous rocks and orthogneisses in Antarctic Peninsula (Graham Land and Marie Byrd Land;Millar et al 2002;Bastías et al 2020) are the potential sedimentary sources that fed the depocenter of basins represented by the Trinity Peninsula Group in Antarctic Peninsula (cf.…”

Petrology and tectonic evolution of late Paleozoic mafic-ultramafic sequences and the Leones Pluton of the Eastern Andean Metamorphic Complex (46-47°S), southern Chile

“…We hypothesize that at the latitude of the study area the northern portion of the Antarctic Peninsula continental block was drifted from the southwestern Gondwana margin as proposed by previous works (cf. Calderón et al, 2016;Suárez et al, 2019;Navarrete et al, 2019). In this scenario, the Devonian and Early Carboniferous orthogneisses in Antarctic Peninsula (cf.…”

“…The study area (46-47ºS) comprises heterochronous metamorphic units without well-defined contacts, grouped in the Eastern Andean Metamorphic Complex (EAMC; Hervé et al, 1998). They consist mainly of Upper Devonian to Triassic polydeformed turbidite successions (Hervé et al, 2003;Augustsson et al, 2006;Suárez et al, 2019), with exceptional intercalations of limestones (marbles), metabasites, and serpentinites (Ramirez-Sánchez et al, 2005;Lacassie, 2003;Quiroz and Belmar, 2010;Hervé et al, 2008;Quitral et al, 2015;Díaz, 2018;Mura, 2018). Our study focus on the petrology of mafic-ultramafic lenses thrusted onto metasedimentary sequences within the EAMC near the western area of Lago General Carrera (Fig.…”