Late Paleozoic geodynamic evolution of the western North Patagonian Massif and its tectonic context along the southwestern Gondwana margin

Abstract

In this study, we propose a geodynamic model covering sedimentation, metamorphism, magmatism, and exhumation processes for the western North Patagonian Massif basement. The youngest detrital zircon population ages (ca. 369 ± 8 Ma) obtained in a schist sample constrains the sedimentation stage to the Carboniferous Period. A first prograde metamorphic stage (M1-D1) produced the main foliation (S1) under greenschist conditions (~ 500 °C; < 4.5 Kbars). This stage was possibly linked to the regional Carboniferous magmatism event (330?300 Ma). The Permian magmatism (ca. 290 Ma) likely induced partial melting and migmatization of the deepest metasedimentary suite. This event corresponds to the second prograde metamorphic stage (M2) that reached amphibolite conditions (690 °C and 6.5 Kbars). The beginning of the basement uplift corresponds to the first retrograde metamorphic stage possibly developed during Permian ? Triassic times (265?235 Ma). This event was triggered by NE-SW compression (σ1) and developed folds (D2-F2), second foliation (S2), micro-textural quartz deformation, and a retrograde evolution path for the garnet-bearing lithofacies. The final stage of the basement exhumation corresponds to the second retrograde metamorphic stage (D3) developed by NNW-SSE compression and linked to open folds (F3) in the Cushamen Formation. The characteristics of the western North Patagonian Massif geodynamic evolution and the adjacent basement regions suggest a paleotectonic subduction setting for the southwestern Gondwana margin during the late Paleozoic times.