Anatectic granites of the Sierras Pampeanas from Córdoba (Argentina): U-Pb SHRIMP and zircon trace element LA-ICP-MS study of diachronic metamorphism and crystallization

espanolEn este trabajo se aportan nuevos datos de edades U-Pb SHRIMP y analisis in situ LA-ICP-MS de elementos traza de circones prove-nientes del granito Rio de los Sauces, Cordoba, Argentina. A partir de marcadas diferencias texturales y composicionales se pudieron identificar dos poblaciones de circones en una misma muestra del granito, las cuales sugieren origenes metamorficos e igneos. Las edades concordia obtenidas en los circones metamorficos e igneos fueron de 537,1 ± 4,8 Ma (2σ) y 529 ± 6 (2σ) Ma, respectivamente. Se interpreta que los circones metamorficos representan el crecimiento en estado solido durante el metamorfismo de alta temperatura de la orogenia Pampeana, durante el inicio o el climax de la anatexia. Por su parte, las edades de los circones igneos representan la edad de cristalizacion del granito Rio de los Sauces. Los datos texturales, composicionales y geocronologicos de ambas poblaciones de circo-nes sugieren que el inicio de la anatexia, la segregacion del fundido y la cristalizacion ocurrieron durante un periodo breve de tiempo de 8 ma. EnglishIn this contribution we present new U-Pb SHRIMP ages and in situ LA-ICP-MS trace element geochemistry of zircon crystals from the Rio de los Sauces anatectic granite, Cordoba, Argentina. Nota-ble difference in texture and composition allowed us to identify two zircon populations in a single granite sample that are interpreted as reflecting metamorphic and igneous origins. Zircons regarded as restitic crystals entrained during the melt segregation yielded a slightly older concordia age of 537.1 ± 4.8 Ma (2σ) than those inter-preted as igneous, dated at 529 ± 6 (2σ) Ma. Inherited metamorphic zircons are interpreted to represent solid-state growth during high temperature metamorphism of the Pampean orogeny at the onset of the anatexis or metamorphic peak. By contrast, igneous zircons would record the crystallization age of Zr within the Rio de los Sauces granite. The textural, compositional and geochronological data of both zircon populations suggest that the inception of the anatexis, the melt segregation and crystallization occurred during a short pe-riod of time of 8 my.