Pahoehoe flows from the central Paraná Continental Flood Basalts

Waichel, Breno Leitão; Lima, Evandro Fernandes de; Lubachesky, Romulo; Sommer, Carlos Augusto

doi:10.1007/s00445-005-0034-5

Cited by 75 publications

(51 citation statements)

References 45 publications

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“…The previous studies concerning facies architecture and geochemistry characterization of the volcanic rocks in the Southern portion of SGF have assumed an effusive nature for the acidic units (Umann et al 2001;Waichel et al 2006;Simões & Lima 2011;Rossetti 2011;Lima et al 2012;Polo & Janasi 2014). In the present work, three profiles of volcanic rocks exposure were investigated.…”

Section: Discussionmentioning

confidence: 92%

The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)

Simões¹,

Rossetti²,

Lima³

et al. 2014

Braz. J. Geol.

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ABSTRACT:The acidic flows from Serra Geral Formation in Torres Syncline, Rio Grande do Sul, Brazil, are on the top of a volcanic sequence composed by a complex facies association of compound, simple and rubbly pahoehoe basic flows, acidic lava domes, and tabular acidic lava flows. The origin and emplacement conditions of the acidic volcanic rocks are discussed in this paper based on petrology, on calculated apatite saturation thermometry temperatures, and on estimated viscosity data. The liquidus temperatures for metaluminous rhyodacite to rhyolite samples are about 1,067.5 ± 25ºC in average. The viscosity (η) values vary from 10 5 to 10 6 Pas for anhydrous conditions, suggesting the emplacement of high-temperaturelow-viscosity lava flows and domes. The occurrence of acidic lava domes above simple pahoehoe flows as flow-banded vitrophyres was under low effusion rates, in spite of their high temperature and low viscosities, which are reflected in their small height. The emplacement of lava domes has continued until the eruption of rubbly pahoehoe flows and the geometry of these deposits rugged the relief. Presence of tabular acidic lava flows covering the landscape indicates that it was under high effusion rates conditions and such flows had well-insulated cooled surface crusts. The capacity to attain greater distances and overpass relief obstacles is explained not only by high effusion rates, but also by very low viscosities at the time of emplacement.

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Section: Discussionmentioning

confidence: 92%

The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)

Simões¹,

Rossetti²,

Lima³

et al. 2014

Braz. J. Geol.

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“…The Gramado type low-Ti basalts correspond to the early PMP volcanic manifestations, and overlay eolian sandstones of the Paraná Basin in the southern portion of the province (Waichel et al, 2006. They were followed by the Esmeralda type basalts, which exhibit, towards the top, intercalations with silicic volcanic rocks of the low-Ti Palmas type (dacites and rhyolites; Bellieni et al, 1986;Garland et al, 1995;Nardy, 1995;Nardy et al, 2008;Waichel et al, 2012).…”

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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“…These studies supplied the basis for the stratigraphic organization and identification of the facies architecture in these provinces (Bondre et al 2004, Jerram 2002, Jerram & Widdowson 2005, Waichel et al 2012. Several studies have indicated that the spreading of these immense volumes of continental basalts was similar to that of the Hawaiian pahoehoe-type flows (Hon et al 1994, Kent et al 1998, Bondre et al 2004, Sheth 2006, Waichel et al 2006.…”

Section: Characterization Of Subaerial Basic Flowsmentioning

confidence: 99%

Morfologia e padrões petrográficos dos derrames pahoehoe e'a'ā da Formação Serra Geral na Sinclinal de Torres (Rio Grande do Sul)

Lima

Waichel

Rossetti

et al. 2012

Rev. bras. geociênc.

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The Serra Geral Formation volcanic sequence in Torres Syncline (Rio Grande do Sul state, Brazil) may be divided into main valley, intermediate zone, and southern hinge. The first volcanic episode along the syncline is characterized by low eruption rates (< 5 m 3 /s) forming compound pahoehoe flows near the dunes and ponded ones in interdune areas. The second episode is constituted by simple flows that rarely exceed 3 m in thickness, erupted with similar eruption rates. The third is defined by ´a´ā flows that are thought to be developed when effusion rates are higher (> 5 -10 m 3 /s). The formation of ´a´ā flows occurred on a plain relief. Pahoehoe and ´a´ā flows have similar chemistry, and the difference in the flow type is related to an increase in eruption rates. The ´a´ā lavas are plagioclase and clinopyroxene phyric, or glomeroporphyritic. All present an intergranular or intersertal microcrystalline groundmass of plagioclase, clinopyroxene, and opaque minerals (<< 0.1 mm in diameter). The pahoehoe lavas differ from the ´a´ā ones in that they have a coarser-grained microcrystalline groundmass. The pahoehoe flows are microcrystalline with glomeroporphyritic and diktytaxitic textures and a plagioclase-poor matrix when compared to ´a´ā lava flows. The higher content of microlites in the ´a´ā flows is attributed to undercooling, higher rate of eruption, and degassing before and during emplacement. When it comes to regional stratigraphic correlation between the Serra Geral Formation flows, the morphological type of the lavas should be taken into account since ´a´ā flows, unlike pahoehoe, do not reach longer distances from the source.Keywords: ´a´ā lava flows; Torres Syncline; Paraná-Etendeka Province; pahoehoe. Resumo Morfologia e padrões petrográficos dos derrames pahoehoe e´a´ā da Formação Serra Geral na Sinclinal de Torres (Rio Grande do Sul).A Formação Serra Geral na Sinclinal Torres, no Rio Grande do Sul, pode ser dividida em uma calha principal, uma zona intermediária e uma ombreira ao Sul. As primeiras manifestações vulcânicas nesta sinclinal marcam condições de taxas de efusão baixas (< 5 m 3 /s), com as lavas do tipo pahoehoe espessas (ponded) ocupando espaços interdunas da Formação Botucatu. O segundo episódio vulcânico é constituído por derrames tabulares que atingem 3 m de espessura em casos excepcionais, com taxas de fusão semelhantes às primeiras manifestações. O terceiro gerou morfologia do tipo ´a´ā, que pode ser atribuído a um aumento nas taxas de efusão, dadas as semelhanças químicas desses com as morfologias pahoehoe. As lavas ´a´ā são constituídas por plagioclásio e piroxênio, sendo geralmente afaníticas ou afíricas, sendo comum também texturas intersetal e glomeroporfirítica, acompanhadas de grande densidade populacional de micrólitos de plagioclásio na matriz (<< 0,1 mm em diâmetro). Os lobos e derrames pahoehoe possuem texturas glomeroporfirítica e diktitaxítica, indicativas de um alto conteúdo de voláteis nos magmas, sendo comparativamente mais granulares. A densidade populacional d...

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Pahoehoe flows from the central Paraná Continental Flood Basalts

Cited by 75 publications

References 45 publications

The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)

The role of viscosity in the emplacement of high-temperature acidic flows of Serra Geral Formation in Torres Syncline (Rio Grande do Sul State, Brazil)

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

Morfologia e padrões petrográficos dos derrames pahoehoe e'a'ā da Formação Serra Geral na Sinclinal de Torres (Rio Grande do Sul)

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