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

CALDERÓN, MAURICIO; GUILLAUME, BENJAMIN; GHIGLIONE, MATÁS; MARTINOD, JOSEPH; SUÁREZ, RODRIGO JAVIER; SUE, CHRISTIAN; ROJO, DIEGO

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2019 vol. 90 p. 471 - 486

0895-9811

The Nunatak Viedma within the Southern Patagonian Icefield has been considered as a volcanic center based onits geomorphologic features, despite the fact that field explorations by Eric Shipton determined its metamorphicnature 70 years ago. We carried out fieldwork to characterize this isolated outcrop and performed the first U-Pbdating in detrital zircons from the basement rocks located inside the Southern Patagonian Icefield. We recognizedvery-low grade metamorphic rocks, corresponding principally to metapelites and metapsammites, andscarce metabasites. Detrital zircons in three metapsammitic samples (composite group of 240 grains) yieldedprominent age population peaks at ∼1090, ∼960, ∼630, ∼520, ∼480?460, ∼380, ∼290?260, ∼235-225 Mathat 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 noveltyLate Triassic age justifies differentiate the Nunatak Viedma Unit from the Devonian-early Carboniferous andPermian-Early Triassic (?) belts of the Eastern Andean Metamorphic Complex. Possible primary source areas forthe 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 EasternAndean Metamorphic Complex. We propose that the cluster of Triassic ages is related to the volcanic arc emplacedalong the Antarctic Peninsula and active at that time when was still attached to southern Patagoniaduring the Triassic. The dynamics of the early Mesozoic orogen is also discussed.