Ordovician igneous and metamorphic units in southeastern Puna: New U–Pb and Sm–Nd data and implications for the evolution of northwestern Argentina

VIRAMONTE, J.M.; BECCHIO, R.; VIRAMONTE, J.G.; PIMENTEL, M.; MARTINO, R.

JOURNAL OF SOUTH AMERICAN EARTH SCIENCES

Elsevier

Lugar: Berlin. Alemania; Año: 2007 p. 167 - 183

0895-9811

New field, petrological, geochemical and geochronological data (U-Pb and Sm-Nd) for Ordovician rock units in southeastern Puna, NW Argentina, allowed us to recognize two lithostratigraphic units in the eastern-northeastern border of salar Centenario: (i) a bimodal volcano-sedimentary sequence affected by a low-medium metamorphism, comprising metasediments associated with basic and felsic metavolcanic rocks, dated at 485 ± 5 Ma. and (ii) 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. Also, have similar Sm-Nd isotopic compositions (TDM model ages between 1.54 Ga. and 1.78 Ga. and åNd (T) values ranging from – 3.2 to – 7.5), which suggest a common origin and derivation of the original magmas by older (Meso-Paleoproterozoic?) continental crust. Mafic rocks show åNd (T) ranging from + 2.3 to + 2.5 indicating a depleted mantle source. The data presented here, combined with those in the literature, suggest that the Ordovician event recycles mainly the pre-existing crust with minor addition of juvenile mantle-derived material.