La Formación Garamilla: evento volcánico del Jurásico Inferior del sector occidental de la Comarca Nordpatagónica, Provincia de Río Negro, Argentina

the garamilla formation cropping out at the western edge of the nordpatagonian region is composed by volcanic and pyroclastic rocks of andesites, dacíticas and rhyolitic compositions whose age extends from the late triassic to early jurassic. in the area of the puestos qui？enao, fuensalida and ca？adones mencué, blancura and currú mahuida appears a sequence 800 m thick where three volcanic events were recognized. the first one consists of domes and rhyolitic lavas, as well as lava-like ignimbrites. the second is represented by dikes and andesitic to dacitic lava flows, lapilli-tuffs and eutaxitic lapilli-tuffs of dacitic composition. the third event is made up of tuffs, rheomorfic tuffs, lapilli-tuffs, volcanic breccias, lava flows and dikes. this unit forms a calc-alkaline series related to a subduction process. an u-pb age of 185 ± 2 ma (pliesbachian) was obtained for the lapilli-tuffs lithofacies of the second volcanic event. these features allow correlation with the lower jurassic calc-alkaline volcanism developed in the neuquén province.