MAPPING THE PERMIAN-TRIASSIC CHOIYOI SILICIC LARGE IGNEOUS PROVINCE IN THE ARGENTINE FRONTAL CORDILLERA (~30°S): INSIGHTS FROM REMOTE SENSING AND ZIRCON U/Pb GEOCRHONOLOGY

The Choiyoi Magmatic Province has been recognized as one of the largest silicic large igneous provinces on Earth based on its areal extent (~900000 km²), estimated volume (~950000 km³) and duration of magmatic activity (~40 Mys). It comprises a series of volcanic and plutonic rocks exposed in western Argentina and Chile (23°–42°S) that record a major magmatic episode during Permian-Triassic time. Choiyoi magmatism is exceptionally well recorded in the Argentine Frontal Cordillera, a high-elevation, thick-skinned structural system that exposes thick sequences (>2500 m) of volcanic rocks, intruded by coeval and younger plutons. Despite ongoing efforts to generate a robust database for these rocks, there are still important regions within the Argentine Frontal Cordillera where the available lithostratigraphic, structural, geochronological and geochemical information is notably scarce. In this work, we combined remote sensing mapping techniques, field observations, and zircon U/Pb geochronology to clarify the stratigraphical and structural framework of Choiyoi volcanism at ~30°S. We performed ASTER multispectral satellite image analyses to improve geological mapping and identify Permian-Triassic units on a large scale. New zircon U/Pb ages obtained by laser ablation ICP mass spectrometry support our interpretation of the ASTER data and indicate a relatively continuous volcanic activity with zircon crystallization ages from coherent igneous and pyroclastic rocks ranging from ~286 and ~241 Ma, but with a major peak in volcanism around 266 Ma. At least three main units can be recognized: 1) lava flows and breccias of andesitic-dacitic (?) composition, with intense propylitic alteration, commonly intercalated with pyroclastic and sedimentary levels (>275 Ma); 2) stacked, relatively quartz-poor thick ignimbrites sheets (~266 Ma); and 3) silicic, quartz-rich ignimbrites (~240 Ma). Finally, the ASTER data outline major faults affecting basal and middle Choiyoi units that may have controlled the emplacement of the volcanic sequences. Our research improves the understanding of the stratigraphy and distribution of the Choiyoi volcanic units and allows us to establish regional correlations with previous age-constrained units.