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vol.48 issue2Geochemistry of the Northern Paraná Continental Flood Basalt (PCFB) Province: implications for regional chemostratigraphyGeology, geochemistry and petrology of basalts from Paraná Continental Magmatic Province in the Araguari, Uberlândia, Uberaba and Sacramento regions, Minas Gerais state, Brazil author indexsubject indexarticles search
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Brazilian Journal of Geology

Print version ISSN 2317-4889On-line version ISSN 2317-4692

Abstract

BESSER, Marcell Leonard; VASCONCELLOS, Eleonora Maria Gouvea  and  NARDY, Antonio José Ranalli. Morphology and stratigraphy of Serra Geral silicic lava flows in the northern segment of the Torres Trough, Paraná Igneous Province. Braz. J. Geol. [online]. 2018, vol.48, n.2, pp.201-219. ISSN 2317-4889.  http://dx.doi.org/10.1590/2317-4889201820180087.

The impetus for this research was the enigma regarding the origin of the extensive silicic volcanic units in the Paraná-Etendeka Igneous Province. Are they rheoignimbrites, lava flows, or a combination of both? The São Joaquim silicic eruptive sequence is comprised of Palmas-Type aphyric dacites and is located in the northern segment of Torres Trough, a dissected mountainous region in southern Brazil. These dacite outcrops form plateaus and remnant hills that are scattered above a basaltic andesitic landscape. The original morphology of the silicic volcanic flows was constrained based on the internal architecture, geometry, and cyclicity of the lithofacies, in conjunction with petrographic and geochemical information. The data suggests the presence of ancient large tabular and lobate silicic lava flows (~100 m thick and ~10-40 km extents). No pyroclastic features were found. Eight interdigitating units were mapped. These large aspect ratios are similar to ones for basaltic flows and those of Snake River-type rhyolites, and they suggest high effusion rates and high temperatures as well as the presence of well-insulated cooled crusts. Lavas would have overflowed from long fissure vents that had created an extensive volcanic silicic surface body composed of conjugated and interdigitated flows above the north segment of the Torres Trough region.

Keywords : Extensive silicic lavas; Paraná-Etendeka Large Igneous Province; Serra Geral volcanism; stratigraphy of Torres Trough; São Joaquim Plateau.

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