Aspectos vulcanológicos dos traquidacitos da região de Piraju - Ourinhos (SP)

Luchetti, Ana Carolina Franciosi

doi:10.11606/d.44.2010.tde-06052010-110329

Cited by 4 publications

(5 citation statements)

References 32 publications

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“…Sandstone intertraps in rhyodacites in the Piraju-Ourinhos region (São Paulo State; Janasi et al, 2007;Luchetti, 2010), where the thick basaltic sequence is missing, were also known. However, until now, there were no reports of features indicating significant time breaks in the upper part of the PMP stratigraphic sequence.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

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

Luchetti¹,

Nardy²,

Machado³

et al. 2014

Solid Earth

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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.

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Section: Discussion and Concluding Remarksmentioning

confidence: 99%

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

Luchetti¹,

Nardy²,

Machado³

et al. 2014

Solid Earth

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show abstract

“…2002) and South American continents (Petry et al, 2007;Waichel et al, 2008). Sandstone intertraps in rhyodacites in the Piraju-Ourinhos region (São Paulo State;Janasi et al, 2007;Luchetti, 2010), where the thick basaltic sequence is missing, were also known. However, until now, there were no reports of features indicating significant time breaks in the upper part of the PMP stratigraphic sequence.…”

Section: Discussion and Concluding Remarksmentioning

confidence: 99%

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

Luchetti¹,

Nardy²,

Machado³

et al. 2013

Preprint

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Abstract. In the Paraná Basin (southern and southeastern Brazil), the stratigraphy of the Paraná Magmatic Province (PMP) is composed of a thick (up to 1600 m) volcanic sequence formed by a succession of petrographically and geochemically distinct units of basic and acidic composition. The whole package may have been emplaced in approximately 3 million yr of almost uninterrupted activity. A few aeolian sandstone layers, indicating arid environmental conditions (Botucatu Formation), are interlayered in the lower basalts. Above the basalts, the Palmas and Chapecó Members of the Early Cretaceous Serra Geral Formation, are composed of silicic volcanic rocks (trachydacites, dacites, rhyolites, and rhyodacites) and basalts. This paper presents new evidence of episodes of sedimentation separating silicic volcanic events, expressed by occurrences 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 Chapecó type rocks and underlying basaltic flows, between silicic bodies of Palmas and Chapecó types, and interlayered with 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.

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“…The manifestation of the high-Ti magmatism began with the effusion of a lesser volume of silicicic lavas (Chapecó type) that directly overlie the Botucatu Formation eolian sandstones in the northern portion of the province (Piccirillo et al, 1987;Janasi et al, 2007b;Luchetti, 2010), or cover the low-Ti Palmas and Esmeralda types volcanic rocks of the central portion of the PMP (Nardy, 1995;Nardy et al, 2008). The high-Ti basalts (Pitanga and Paranapanema types) are the latest volcanic manifestations of the PMP, covering the northern and western regions of the Paraná Basin (Peate et al, 1992;Peate, 1997).…”

Section: Stratigraphymentioning

confidence: 99%

Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná Magmatic Province, Brazil

Polo

Janasi

2014

Geol. USP, Sér. cient.

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This article presents the first map in detail scale for an area covered by Palmas type volcanic rocks in the south border of the eocretaceous Paraná Magmatic Province, south Brazil. The study of the structural features coupled with petrography and geochemistry made it possible to separate these rocks into three main volcanic sequences and recognize their stratigraphy. The older Caxias do Sul sequence rests directly over the first low-Ti basalt flows (Gramado type), and corresponds to the stacking of lobated lava flows, laminar flows and lava domes, mostly emitted as continuous eruptions; only the latest eruptions are intercalated with thin sandstone deposits. These rocks have dacitic composition (~ 68 wt% SiO 2 ) with microphenocrysts of plagioclase and subordinate pyroxenes and Ti-magnetite immersed in glassy or devitrified matrix. A second volcanic sequence, named Barros Cassal, is composed of several lava flows of basaltic andesite, andesitic and dacitic composition (~ 54; ~ 57 and ~ 63 wt% SiO 2 , respectively), with microphenocrysts of plagioclase, pyroxenes and Ti-magnetite. The frequent intercalation of sandstone between the flows attests to the intermittent behaviour of this event. The upper sequence, Santa Maria, is made up of more silica-rich (~ 70 wt% SiO 2 ) rocks occurring as laminar flows, lobated flows and lava-domes. These rocks have rhyolitic composition with microphenocrysts of plagioclase and Ti-magnetite set in a glassy or devitrified matrix with microlites. The structures and textures of all three silicic sequences favor the interpretation that they had a predominantly effusive character, which is thought to be a reflection of the remarkably high temperatures of the lavas (~ 1,000 ºC).Keywords: Volcanic stratigraphy; Silicic lavas; Paraná Magmatic Province; Palmas type. ResumoEste artigo apresenta o primeiro mapa em escala de detalhe de uma área coberta pelas rochas vulcânicas tipo Palmas, na borda sul da Província Magmática Paraná, de idade eocretácica. O estudo das características estruturais, juntamente com a petrografia e geoquímica, permitiu separar as rochas em três sequências vulcânicas principais, reconhecendo a sua estratigrafia. As rochas da primeira sequência, denominada Caxias do Sul, recobrem fluxos basálticos de baixo Ti (tipo Gramado), e correspondem a um empilhamento de derrames lobados, fluxos laminares e lava domos, emitidos por erupções contínuas. O final da atividade vulcânica é marcado por erupções mais intermitentes, permitindo assim a intercalação de delgados depósitos de arenitos. Estas rochas têm composição dacítica (~ 68 %, em peso, SiO 2 ) com microfenocristais de plagioclásio, piroxênios e Ti-magnetita imersos em matriz vítrea ou desvitrificada. A segunda sequência, denominada Barros Cassal, é composta por diversos fluxos de lavas de andesito basáltico, andesito e dacito (~ 54; ~ 57 e ~ 63%, em peso, SiO 2 , respectivamente), com microfenocristais de plagioclásio, piroxênios e Ti-magnetita. A frequente intercalação de arenitos entre os fluxos atesta o comp...

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Aspectos vulcanológicos dos traquidacitos da região de Piraju - Ourinhos (SP)

Cited by 4 publications

References 32 publications

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

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

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

Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná Magmatic Province, Brazil

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