Characterization of volcanic structures associated to the silicic magmatism of the Paraná-Etendeka Province, in the Aparados da Serra region, southern Brazil

Abstract

The Paraná-Etendeka Magmatic Province is associated with the distensive tectonics that caused the rupture of the Gondwana continent during the Lower Cretaceous and generated an intense volcanism that covers South America and the NW portion of Namibia in Africa. In Brazil, this volcanic sequence is named Serra Geral Group and predominantly consists of basalts and subordinated silicic rocks. The goal of this study is to characterize the geomorphological features observed in the Aparados da Serra region, southern Brazil, and to evaluate the relationship between these structures and the primary silicic volcanic structures. The geomorphological features were fi rst identifi ed using remote sensing and then correlated with fl ow structures observed in the fi eld, as well as petrographic and geochemical data. AMS data were used to determine magnetic patterns and the direction of magmatic fl ow of the rocks. Despite the low degree of anisotropy, clear patterns of lineation and foliation were identifi ed in the studied rocks. Our data shows that Units I and II correspond to silicic lava fl ows linked to effusive fi ssure eruptions, presenting a dome morphology caused by differential erosion. Unit III rocks may correspond to true volcanic domes, whereas the Unit IV corresponds to the effusive feeder structures.

Facies architecture and volcanological aspects of silicic rocks from the Palmas plateau, Brazil

“…Discussion on the origin of Palmas-type rocks dates back to the pioneering mapping and geochemical characterization studies of the PIP (e.g., Bellieni et al 1986). However, it was only in the last decade, based on physical volcanology criteria, that more robust models were proposed (Waichel et al 2012, Polo and Janasi 2014, Polo et al 2018a, Besser et al 2018, Luchetti et al 2018a, Benites et al 2020. Luchetti et al (2018b) indicated a pyroclastic origin for Palmas-type rocks that occur in central parts of the PIP (including those described in southwestern Paraná State), characterizing them as high-grade ignimbrites.…”

“…Although amygdales are only occasionally present in most lithofacies, in Ram and Ral they account for up to 35% of the total rock volume. In these cases, the amygdales are generally flattened parallel to the planar disjunction and aligned parallel to the flow direction (e.g., Polo et al 2018b, Benites et al 2020. Ram amygdales are mostly filled with chalcedony, while in intensely altered Ral, they are filled with clay materials ( Fig.…”

“…In this case, the abnormally high effusion temperature (930-1,010°C) and low H 2 O content (~1-2 wt.%) would be responsible for the low viscosity values (Nardy 1995, Polo et al 2018a and, consequently, the widespread distribution of the rocks. Effusive models involve extensive tabular flows and lateral coalescence of domes and coulées (Umann et al 2001, Besser et al 2018, Polo and Janasi 2014, Benites et al 2020. Some of these authors (e.g., Umann et al 2001, however, do not disregard the presence of volumetrically subordinate pyroclastic rocks among the sicilic volcanites of the province.…”

Evolution Magmatism of Nagasari Volcano Dieng, Central Java, Indonesia

“…The stratigraphic sequence from oldest to youngest includes: Pyroclastic flows are fast-moving flows of hot gas and volcanic material or tephra. The hot volcanic material flows along the volcanic valley at a speed of 100 to 700 km/hour with a temperature of around 1,000 °C (Branney and Kokelaar, 2002), (Branney and Kokelaar, 2017;Benites et al, 2020). The pyroclastic flow of this unit in the study area is a product of the Prau Volcano.…”

Raw materials and functional designs of Fishtail projectile points from southern Brazil

“…The BSGC includes the sandstones of the Botucatú Formation (Jurassic -Cretaceous aeolian sandstones), originated under an arid desert climate, on which the lavas of the Serra Geral Formation flowed, as a consequence of the Atlantic Ocean opening, and which covered most of the surface of the southern States of Brazil. They are formed mainly by tholeitic basalts (90%), andesites (7%) and rhyodacites-rhyolites (3%) (Piccirillo & Melfi 1988: 123;Benites et al 2020), where different facies were recognized (Wildner et al 2006(Wildner et al : 17, 2007. These basalts form the hills and the bedrock (~ 500 m thick on average, up to several km) below the topsoils, except in the coastal area and the surroundings, where other geological formations emerge, and the more complex geology of the Paraná basin is exposed (see Supplementary file 3).…”