Geologic occurrence shape of pyroclastic rock dykes in the Dona Eugênia River Valley, Municpal Parl of Nova Iguaçu, Rio de Janeiro
Authors
Akihisa Motoki
Departamento de Mineralogia e Petrologia Ígnea, Universidade do Estado do Rio de Janeiro (DMPI/UERJ)
Rodrigo Soares
Departamento de Mineralogia e Petrologia Ígnea, Universidade do Estado do Rio de Janeiro (DMPI/UERJ)
Ana Maria Netto
Departamento de Geologia Regional e Geotectônica, Universidade do Estado do Rio
Susanna Eleonora Sichel
Laboratório de Geologia Marinha (LAGEMAR), Universidade Federal Fluminense
José Ribeiro Aires
Marcela Lobato
Departamento de Mineralogia e Petrologia Ígnea, Universidade do Estado do Rio de Janeiro (DMPI/UERJ).
Keywords:
dique piroclástico, solda, traquito, vulcão, fissura subvulcânica, Nova Iguaçu.
Abstract
This article presents field descriptions and the volcanological interpretation of the pyroclastic rocks that outcrop along the Dona Eugênia River Valley, Nova Iguaçu Municipal Park, State of Rio de Janeiro, Brazil. These rocks form dyke-like bodies of metric width, intrusive into alkaline syenite and trachyte. The contact planes are sharp, flat, and sub-vertical, without intercalation of palaeosoil and organic materials. The clasts are made up of the syenite and second-generation trachyte. The matrix is highly consolidated due probably to welding and characterised by intense sericitisation and calcite dissemination. These observations indicate that these pyroclastic rocks are not constitutes pyroclastic flow deposit, nor fault breccia, but subvolcanic fissure vents that fed the pyroclastic materials of kilometric depth.
Keywords: Pyroclastic dyke, welding, trachyte, volcano, subvolcanic fissure, Nova Iguaçu.
