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

• Autores: Suárez, Rodrigo Javier; Ghiglione, Matías Carlos; Calderón, Mauricio; Sue, Christian; Martinod, Joseph; Guillaume, Benjamin; Rojo, Diego
• Año de publicación: 2019
• Idioma: inglés
• Tipo de recurso: artículo
• Materia: Ciencias Exactas y Naturales; Nunatak Viedma; Very-low Grade Metamorphic Rocks; Detrital Zircons Ages; Antarctic Peninsula; Southern Patagonian Andes; Southwestern Gondwana; Ciencias Exactas y Naturales
• Institución: Universidad Nacional de Río Negro

Fil: Suárez, Rodrigo Javier. Instituto de Estudios Andinos IDEAN (Universidad de Buenos Aires - CONICET), Buenos Aires, Argentina
Fil: Ghiglione, Matías Carlos. Instituto de Estudios Andinos IDEAN (Universidad de Buenos Aires - CONICET), Buenos Aires, Argentina
Fil: Calderón, Mauricio. Carrera de Geología, Facultad de Ingeniería, Universidad Andres Bello, Santiago, Chile.
Fil: Sue, Christian. CNRS-UMR6249, Université de Bourgogne Franche-Comté, Besançon Cedex, France.
Fil: Matinod, Joseph. ISTerre, Université de Savoie Mont-Blanc, Le Bourget du Lac cedex, France.
Fil: Guillaume, Benjamin. Université Rennes, CNRS, Géosciences Rennes. Rennes, France
Fil: Rojo, Diego. Facultad de Ingenieria y Arquitectura, Universidad Arturo Prat, Iquique, Chile
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 time when was still attached to southern Patagonia during the Triassic. The dynamics of the early Mesozoic orogen is also discussed.
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