New insights on the occurrence of peperites and sedimentary deposits within the silicic volcanic sequences of the Paraná Magmatic Province, Brazil

Abstract

Abstract. The PMP (Paraná Magmatic Province) is characterized by lava flows of the Early Cretaceous Serra Geral Formation which covers about 75 % of the Paraná Basin (southern and southeastern Brazil), composed of a thick (up to 1600 m) volcanic sequence formed by a succession of petrographically and geochemically distinct units of basic and silicic composition. The whole package must have been emplaced during approximately 3 million years of nearly uninterrupted activity. A few aeolian sandstone layers, indicating arid environmental conditions (the Botucatu Formation), are interlayered in the lower basalts. Above the basalts, the Palmas and Chapecó Members are composed of silicic volcanic rocks (quartz latites, dacites, rhyodacites and rhyolites) and basalts. This paper presents new evidence of sedimentation episodes separating silicic volcanic events, expressed by the occurrence of sedimentary deposits. Interaction between the volcanic bodies and the coeval unconsolidated sediments formed peperites. The sediments were observed between basaltic lava flows and silicic rocks or interlayered in the Palmas-type rocks, between the Chapecó-type rocks and overlying basaltic flows, between silicic bodies of the Palmas and Chapecó types, and interlayered within Palmas-type units. The observed structures indicate that the sediments were still wet and unconsolidated, or weakly consolidated, at the time of volcanism, which, coupled with the sediment features, reflect environmental conditions that are different from those characterizing the Botucatu arid conditions.

Silicic, high- to extremely high-grade ignimbrites and associated deposits from the Paraná Magmatic Province, southern Brazil

“…Peperites are frequently found at the base and interlayered within the silicic volcanic sequence (Luchetti et al, 2014), indicating periods of subaerial sedimentation before and between the silicic volcanic eruptions.…”

Volcanological aspects of the northwest region of Paraná continental flood basalts (Brazil)

“…In the NW-PCFB, the basic lava interaction with wet, fine-grained sandstone resulted in fluidal peperites, whereas those containing irregular juvenile clasts are found in the central PCFB (Waichel et al, 2007(Waichel et al, , 2008. In addition, the jigsaw-fit texture peperites associated with rhyolites are reported for the southern PCFB by Luchetti et al (2014). The fluidal peperites associated with pahoehoe lavas of the NW-PCFB seem to be very similar to those of Hawaii.…”

“…Therefore, it is most likely that the effusive materials have such low viscosities (10 1 -10 3 Pa s; McBirney and Murase, 1984) and eruption temperatures ranging near liquidus (∼ 1150 • C; Helz and Thornber, 1987;Cashman et al, 1999). Instead, the rhyolite lavas that generated the peperites reported by Luchetti et al (2014) have the same characteristics as those found in Passamaquoddy Bay (Dadd and Van Wagoner, 2002), with low temperatures (∼ 800 • C) and high viscosity (10 8 -10 10 Pa s).…”

“…The investigations were carried out by Petry et al (2007) and Waichel et al (2007Waichel et al ( , 2008 for basalt flows and Luchetti et al (2014) for basalt and rhyolite flows or ignimbrites. According to these workers, the textures of the mafic peperite breccia vary from globular to amoeboid (anhedral form), while the rhyolitic ones range from blocky (also called jigsaw-fit) to irregular form (subhedral form).…”

Sediment-infill volcanic breccia from the Neoarchean Shimoga greenstone terrane, western Dharwar Craton: Implications on pyroclastic volcanism and sedimentation in an active continental margin

“…Dimitriadis, 2013; Luchetti et al, 2014). However, the occurrence of sediment-infill volcanic breccias in association with the Daginkatte rhyolites in the Neoarchean Shimoga belt is not in compliance with the above process for their generation and suggests an active continental margin setting marked by explosive volcanism and subsequent sedimentation.…”