Tertiary volcanism and sedimentation in the southern Cordillera Principal, Mendoza, Argentina

The tertiary sedimentation of the Cordillera Principal, to the south of the Province of Mendoza is characterized by a paleoenvironmental evolution responding to the tectonic evolution of the thrust and folded belt and to the volcanic evolution of the contemporary magmatic arc . This combination of events created a sedimentary and volcaniclastic column, which is briefly described below, including a stratigraphie classification . The studied sedimentary seq uences as weil as the contemporary volcanic bodies crop out to the south of the Province of Mendoza, from the Diamante River in the north to the Molle Ca isson in the south. Paleogene Pircala -Coihueco Fonnation (Maastrichtian? - Thanetian) The Pircala-Coihueco formation is distributed on a regional basis. This unit, as a whole, is characterized by a sequence of fine sandstones showing reddish to purplish colors. The lower limit is transitional with the Roca Formation and the upper limit shows a regional discordance that separates it from the Agua de la Piedra Formation. It shows three well-differentiated sections. The lower section shows interweaved pyroclastic levels (63.5 ± 3.2 to 58.4 ± 2.9 Ma, Parras el al, 1998 and Parras and Casadio 1999) that would belong to a fluvial system with a low to moderate sinuosity, which probably deveJoped within the flooded plain; the mid section shows mature paleosoil levels that have been primarily eroded by gravelly fluvial systems. The tectosedimentary evolution of these deposits is due to the combination of volcanic arc activity, the Danian regression and an increase in the supply area, primarily in the mid and high-basin areas . Combina and Nullo (2002) recognize an intraformational variation within this Unit, positioning it at the paleosoil level; it would belong to the activity during the Incaic Phase. The arc was located to the west-southwest of the stud ied area (Mendez el al, 1995). The upper seetor of this unit responds to the growth of the synorogenic prism, which in turn responds to the initi al uplift pulses ofthis sector of the range, which is 55 Ma., as minimum.