Significance of the early Jurassic Garamilla formation in the Western Nordpatagonian Massif

Abstract

By means of facial, stratigraphic, petrographic, geochemical and geochronological studies we characterize the Garamilla Formation, cropping out in the western Nordpatagonian Massif. The studies of these volcanic rocks reveal an Early Jurassic volcanic episode calc-alkaline series. Other geochemical features reveal a progressive change formed by three volcanic units that change from normal calc-alkaline to high-K 13 from an initial subduction-related volcanism to one intraplate-related volcanism. This volcanic episode is temporally and geochemically equivalent to those volcanic units located in half-grabens in several areas of the Neuquén Basin. The volcanic units were erupted in different structural designs. A portion of its depocenter was interpreted as a transtensional half-graben whereas the other exhibits a trapdoor structure. The lineament trends that bound the volcanic system were also recognised in Western Nordpatagonian Massif, and were assigned to the Gondwanide Orogenic.