Early Paleozoic long-lived silicic volcanism in the Eastern Puna Magmatic Belt, Argentina

Abstract

In several locations along the Eastern Puna Magmatic Belt (EPMB) porphyritic rhyolite facies are interbedded with thinly bedded mudstone and fine-grained sandstone deposited during deepening of the marine setting. Previous research mainly focused on the northern part of EPMB, identified four main syn-sedimentary rhyolitic-dacitic volcanic episodes from Early to Late Ordovician, the oldest being Tremadocian (earliest Ordovician). In this contribution, we describe coherent rhyolite facies associated with volcaniclastic breccias in the central part of the EPMB (Cajón, Tuzgle, Concordia and Agua de Castilla creeks), and we present new geochemical data and U/Pb zircon ages on coherent rhyolite facies (Cajón, Huancar and Opla). The studied rhyolites are syn-sedimentary sills with peperitic margins. The coherent rhyolites have SiO2 content of ∼65–71 wt%, peraluminous signature, enrichment in LILE (Cs, Rb, Ba) and marked negative Sr, Ti and P anomalies. The REE patterns normalized to chondrite show a higher content of the light REE and a negative Eu anomaly (Eu/Eu* between 0.44 and 0.52). The integration of the regional data with our results suggests that at least two rhyolitic-dacitic volcanic episodes occurred during the Ordovician evolution of the EPMB: The Early Ordovician (∼485-462 Ma) including Tremadocian and Arenigian facies (Rio Taique, Niño Muerto, Huancar, Opla, northern Pastos Chicos, Agua Cavada, Muñayoc, oldest Quichagua, Cordón de Escaya, Cajón, Tuzgle, Concordia and Agua de Castilla); and the youngest Late Ordovician facies (∼449-443 Ma; Oplita, southern Pastos Chicos, Cordón de Escaya and youngest Quichagua). Hence, sedimentation and silicic volcanism across the Eastern Puna Magmatic Belt spanned at least in two episodes along the Ordovician period with more volume and duration during the Early Ordovician (ca. 20 Ma).