Tipos de Derrame e Reconhecimento de Estruturas nos Basaltos da Formação Serra Geral: Terminologia e Aspectos de Campo

Studies focusing the flow morphology and structures of the basalts of Serra Geral Formation (west of Paraná State, Brazil) make possible the identification of pahoehoe and 'a'a flows, with predominance of simple and compound pahoehoe. This terminology was created in the Hawaiian Archipelago and was previously applied to the Columbia River Basalts and Deccan Plateau, and can also be used in the investigation of the Serra Geral Formation. The compound pahoehoe flows are formed by Ptype (pipe) and S-type (spongy) lobes. Surface features related with the pahoehoe and aa flows are well preserved in Serra Geral Formation. The flows have lateral extension of up to 50 km and can be divided in three portions in relation to the conduit: proximal, medium and distal. In the proximal portion the flows are thick (40-70 m) and the contact between the superior crust and the massive core is sharp. In the medium portion predominate simple pahoehoe flows with thickness between 20 and 30 m; locally occur compound pahoehoe. The distal portion is formed by compound flows (up to 5 m thick) with a few lobes. The emplacement of the pahoehoe inflated flows in the studied area suggests low eruption rates.