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

M QUIROGA; ARNOSIO MARCELO; BECCHIO RAÚL; EMILCE BUSTOS; BAEZ WALTER

Congreso; XVI Reunión Argentina de Sedimentología; 2018

In old successionsthe correct interpretations of different types of volcaniclastic deposits associatedto coherent rhyolites is key to the determination of intrusive and extrusiverhyolite facies (sills vs domes). Strong deformation and hydrothermalalteration could omit some primary textures and generate different texturesthat resemble other deposits. In other words, many sediment-matrix igneousbreccia could share many characteristics with peperites but they are notalways, and wrong interpretations of intrusive facies could be very common. The Complejo dePlataforma de la Puna outcrops along Sierra de Cobres (SC) and represents aLower Paleozoic submarine volcanic system emplaced contemporaneously withmarine sedimentary sequences in back-arc setting. In SC, Huancar, Agua Cavada,Opla and Pastos Chicos areas were selected to study the volcanic faciesarchitecture through many traverses. We identified six facies: coherentfeldspar-phyric rhyolite facies (Cr), green-mudstone facies (Gm), blue-mudstonefacies (Bm), monomictic-rhyolite breccia facies (Mbx), mudstone-matrix rhyolitebreccia facies (Mmbx) and silicified mudstone-matrix rhyolite breccia facies(Smbx). Petrographic studies and detailed correlations interpret Mbx as ahyaloclastite, Mmbx as a sediment-infill volcanic breccia and Smbx as apeperite. In Huancar and AguaCavada, Cr facies show gradational contacts with Mbx and Smbx and they areinterpreted as an intrusive facies like as sills. In Opla area and someoutcrops from Agua Cavada and Huancar, Cr facies show gradational contacts withMmbx and they are interpreted as an extrusive facies like as domes.