CORRECT INTERPRETATION OF VOLCANICLASTIC DEPOSITS AS A GUIDE TO DISTINGUISH INTRUSIVE AND EXTRUSIVE FACIES IN RHYOLITE UNITS, ARGENTINA PUNA

MIRTA QUIROGA; BUSTOS E.; MARCELO ARNOSIO; BAEZ WALTER; BECCHIO RAÚL

Congreso; Reunión Argentina de Sedimentología; 2018

In old successions the correct interpretations of different types ofvolcaniclastic deposits associated to coherent rhyolites is key to the determination of intrusive and extrusive rhyolite facies (sills vs domes). Strong deformation and hydrothermal alteration could omit some primary textures and generate different textures that resemble other deposits. In other words, many sediment-matrix igneous breccia could share many characteristics with peperites but they are not always, and wrong interpretations of intrusive facies could be very common. The Complejo de Plataforma de la Puna outcrops along Sierra de Cobres (SC) and represents a Lower Paleozoic submarine volcanic system emplaced contemporaneously with marine sedimentary sequences in back-arc setting. In SC, Huancar, Agua Cavada, Opla and Pastos Chicos areas were selected to study the volcanic facies architecture through many transects. We identified six facies: coherent feldspar-phyric rhyolite facies (Cr), green- mudstone facies (Gm), blue-mudstone facies (Bm), monomictic-rhyolite breccia facies (Mbx), mudstone-matrix rhyolite breccia facies (Mmbx) and silicified mudstone-matrix rhyolite breccia facies (Smbx). Petrographic studies and detailed correlations interpret Mbx as a hyaloclastite, Mmbx as a sediment-infill volcanic breccia and Smbx as a peperite. In Huancar and Agua Cavada, Cr facies show gradational contacts with Mbx and Smbx and they are interpreted as an intrusive facies like as sills. In Opla area and some outcrops from Agua Cavada and Huancar, Cr facies show gradational contacts with Mmbx and theyare interpreted as an extrusive facies like as domes.