Upper Paleozoic peperites at the northern margin of the Mendoza River, eastern border of the Cordillera Frontal

Abstract

An outcrop of Tambillos Formation of the Choiyoi Group is described. It is composed mostly by peperites, being recognized the types amoeboid, globular, blocky and of mixed morphologies. The lavas that gave origin to these rocks had intermediate or acid compositions with scarce oligoclase and biotite phenocrysts, and the sediments which they had interacted were of volcanic origin. In the outcrop, sectors of lavas and laminated sandstones are also described, and constitute a complex that would have originated by the irruption of lava in the bottom of a lake of about 130 km². The rocks were affected by argillic alteration and silicification. The complex was intruded by basaltic dikes that belong to another magmatic cycle. The area is proposed as a site of geologic interest based on its accessibility, magnitude and quality of the outcrops, which illustrate an uncommon paleovolcanic process, occurred during the Late Paleozoic.