Novo Hamburgo Complex formed by hydrothermal, explosive injection of Botucatu erg sand into extensive tracts of Paraná Volcanic Province (S Brazil)

Abstract

The Parana Volcanic Province follows Siberia as the second largest in the continents and offers a unique opportunity to study the hydrothermal relationship between basalt-rhyodacite lavas and buried erg-turned aquifer in an intraplate setting. Injected sand fluidized after basalt sealing and was succeeded by amethyst and agate geode opening and filling. Excellent exposures in the Herveiras cuesta, southern Brazil, allow the comparison of processes over long distances (1500 km) in the volcanic group. Fieldwork and basalt chemistry led to the identification of three hydrothermal processes-amygdales filling (H1), sand injection (H2) and amethyst geodes formation (H3). Sand injection was triggered by high temperature (150 ℃) and seismicity. These low-temperature processes identified in the Herveiras cuesta demonstrate the homogeneity of relationships between the paleoerg, giant aquifer and intraplate volcanic rocks across the volcanic province.