Geoquimica y significado tectonico-deposicional de pelitas y margas cretacico-terciarias del noreste de la Patagonia argentina

Abstract

ABSTRACT. Geochemistry and tectonic-depositional meaning of cretaceous-tertiary pelites and marls from northeastern Argentinian Patagonia. Through major element geochemistry, compositional characterization and statistic analysis of chemical data, two normative associations (quartz-illite and smectite) have been defined in Cretaceous-Tertiary pelites and marls from the North Patagonian Massif. The quartz-iIIite detrital association is related to the crystalline basement, and was formed under low-energy tidal and wave conditions. The smectite association suggests pyroclastic processes and very fine fall-out deposition in standing water bodies. According to general interpretation of geochemical data, the studied fine-grained rocks could be related to active tectonic regions. This geotectonic imprint is due to the low K2O/Na2O values and the high content of normative smectite; however, these features are exclusively assigned here to the volcanic provenance. The Cretaceous-Tertiary marine pelites and marls were deposited in an extensional and passive basin characlerized by its proximity to the Andean magmatic arc, from which many of the siliciclastic components were derived.