Peperite formed by lava flows over sediments: An example from the central Paraná Continental Flood Basalts,Brazil |
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| Authors: | Breno L Waichel Evandro F de Lima Carlos A Sommer Romulo Lubachesky |
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| Institution: | 1. Universidade Estadual do Oeste do Paraná (UNIOESTE), Rua Universitária 1619, Cx.P. 701, CEP 85819-110, Cascavel, PR, Brazil;2. Departamento de Mineralogia e Petrologia, Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves, 9500, Cx.P. 15001, CEP 91501-970, Porto Alegre, RS, Brazil;3. Instituto de Geociências, Universidade Federal do Rio Grande do Sul (UFRGS), Av. Bento Gonçalves, 9500, Cx.P. 15001, CEP 91501-970, Porto Alegre, RS, Brazil |
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| Abstract: | Pahoehoe flows interbedded with sediments have been identified in the superior portion of Paraná Continental Flood Basalts (PCFB), west portion of Paraná State, southern Brazil. In the study area peperites are generated by the interaction between lava flows and wet lacustrine sediments (silt and clay). Evidence that the sediments were unconsolidated or poorly consolidated and wet when the lava flowed over them includes vesiculated sediment, sediment in vesicles and fractures in lava flow and in juvenile clasts in the peperite and soft sediment deformation. Hydrodynamic mingling of lava and wet sediments (coarse mingling) is predominant and volcanic rocks and textures related to explosive phase of Molten Fuel Coolant Interaction (MFCI) are not observed in study area. Locally centimeter-sized areas display direct contact between ash-sized juvenile clasts and sediments formed by the collapse of a vapor film. The textures of fluidal peperites in the central PCFB indicate that the relevant factors that led to a coarse mingling between lava/sediment are (1) lava properties (low viscosity); (2) fine grained, unconsolidated or poorly consolidated wet sediment; and (3) a single episode of interaction between lava flows and sediment. |
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| Keywords: | peperite lava flow&ndash sediment interaction coarse mingling subaerial volcanism Paraná CFB |
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