Structural and petrographic constraints on the stratigraphy of the Lapataia Formation, with implications for the tectonic evolution of the Fuegian Andes

CAO, SEBASTIÁN J.; TORRES CARBONELL, PABLO J.; DIMIERI, LUIS V.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2018 vol. 84 p. 223 - 241

0895-9811

The structure of the Fuegian Andes central belt is characterized by a first phase of peak metamorphism andductile deformation, followed by a brittle-ductile thrusting phase including juxtaposition of different (firstphase) structural levels; both related to the closure and inversion of the Late Jurassic-Early Cretaceous RocasVerdes basin. The second phase involved thrust sheets of pre-Jurassic basement, as well as Upper Jurassic andLower Cretaceous units from the volcanic-sedimentary fill of the basin. Rock exposures in the Parque NacionalTierra del Fuego reveal a diversity of metamorphic mineral assemblages, dynamic recrystallization grades andassociated structures, evidencing a variety of protoliths and positions in the crust during their orogenic evolution.Among the units present in this sector, the Lapataia Formation portrays the higher metamorphic gradereported in the Argentine side of the Fuegian Andes, and since no precise radiometric ages have been establishedto date, its stratigraphic position remains a matter of debate: the discussion being whether it belongs to the pre-Jurassic basement, or the Upper Jurassic volcanic/volcaniclastic initial fill of the Rocas Verdes basin. Themapping and petrographic/microstructural study of the Lapataia Formation and those of undoubtedly Mesozoicage, allow to characterize the former as a group of rocks with great lithological affinity with the Upper Jurassicmetamorphic rocks found elsewhere in the central belt of the Fuegian Andes. The main differences in metamorphicgrade are indebted to its deformation at deeper crustal levels, but during the same stages than theMesozoic rocks. Accordingly, we interpret the regional structure to be associated with the stacking of thrustsheets from different structural levels through the emplacement of a duplex system during the growth of theFuegian Andes