Resumo

RISSO, Corina  e  APARICIO, Alfredo. Segregation structures in basaltic-andesitic lavas of Decepción island (Antarctica). Geoacta [online]. 2014, vol.39, n.2, pp.68-77. ISSN 1852-7744.

Segregation structures in the form of pipe vesicles, normally described in bibliography only in basaltic lava flows occur in basaltic-andesitic pillow lavas on Deception Island, Antarctica. The genesis of pipe vesicles in these basaltic-andesitic lavas involved the amalgamation of many small gas vesicles that escaped towards the pillows. These gases modified the conditions of crystallisation at the rim of the vesicles, slightly altering the chemistry and texture of the adjacent rock. This process was synchronous with or slightly-earlier than a secondary process of general oxidation of the host rock caused by fluids that were retained inside the vesicles before later escaping. Mineralogy and chemistry of the rim of the pipe vesicles and host rock suggest they both derive from a single magma. Physico-chemical processes during crystallisation caused a concentration of fluids that modified the chemistry, texture and crystallinity of the original magma at the edges of the pipe vesicles. We suggest that the formation of pipe vesicles could be better explained from the movement and interaction of fluids, which may be sea water vapor / ice-snow and / or volcanic fluids.

Palavras-chave : Pipe vesicles; Basaltic-andesites; Deception Island; Antarctica.

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