Ordovician igneous and metamorphic units in southeastern Puna: New U–Pb and Sm–Nd data and implications for the evolution of northwestern Argentina |
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| Authors: | Jos María Viramonte Raúl Alberto Becchio Jos Germn Viramonte Marcio Martins Pimentel Roberto Donato Martino |
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| Institution: | aInstituto Geonorte, Universidad Nacional de Salta and CONICET. Buenos Aires 177, Salta 4400, Argentina;bLaboratorio de Geocronología. Instituto de Geociências, Universidade de Brasilia. Brasília-DF 70910-900, Brazil;cUniversidad Nacional de Córdoba, FCEFyN and CONICET. Av. Vélez Sarsfield 1611, Ciudad Universitaria, Córdoba 5000, Argentina |
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| Abstract: | New field, petrological, geochemical, and geochronological data (U–Pb and Sm–Nd) for Ordovician rock units in the southeastern Puna, NW Argentina, indicate two lithostratigraphic units at the eastern–northeastern border of salar Centenario: (1) a bimodal volcanosedimentary sequence affected by low- to medium-grade metamorphism, comprising metasediments associated with basic and felsic metavolcanic rocks, dated 485 ± 5 Ma, and (2) a plutonic unit composed of syenogranites to quartz-rich leucogranites with U–Pb zircon ages between 462 ± 7 and 475 ± 5 Ma. Felsic metavolcanic and plutonic rocks are peraluminous and show similar geochemical differentiation trends. They also have similar Sm–Nd isotopic compositions (TDM model ages of 1.54–1.78 Ga; εNd(T) values ranging from −3.2 to −7.5) that suggest a common origin and derivation of the original magmas from older (Meso-Paleoproterozoic?) continental crust. Mafic rocks show εNd(T) ranging from +2.3 to +2.5, indicating a depleted mantle source. The data presented here, combined with those in the literature, suggest Ordovician magmatism mainly recycles preexisting crust with minor additions of juvenile mantle-derived material. |
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| Keywords: | Ordovician Granites Metamorphic rocks Southern Puna U– Pb zircon age TDM |
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