Fluidized sand effusion over successive basalt flows of the northwestern Paraná volcanic province

Abstract

A remarkable sand injectite complex (1 million km2) is hosted in Paraná volcanic province, South America, and is here described. Named Novo Hamburgo Complex, these sand injectites originated by the interaction of several major geological processes, as presently described in Campo Grande and Serra de Maracaju cuesta, Mato Grosso do Sul, Brazil. The geologically unique relationship of a major continental flood basalt province with the underlying large freshwater Guarani aquifer – hosted in paleodune sands of the largest known paleoerg – resulted in a network of sand injectites where each basalt lava flow was injected and then covered by sand extrudite. The basaltic lavas were individualized by chemical characteristics and correlated (with cover extrudite) along the escarpment of the cuesta for 10–30 km. After cooling, each volcanic unit underwent prolonged hydrothermal alteration. Porosity vanished by sealing with chalcedony during continued percolation of hot water. The process culminated in the explosive injection and effusion of fluidized sand, resulting in the covering of each lava flow with a sand extrudite. Lavas were sealed in sequence above the underlying aquifer, resulting in the explosive injection and effusion of fluidized sand. The interplay of three major geological features was required in the Cretaceous Paraná Basin to build the geology of Serra de Maracaju and Novo Hamburgo Complex: (1) a huge continental flood basalt province, (2) a huge underlying paleoerg, and (3) a large, underlying Guarani aquifer. An infinite volume of hot water and its vapor was available for the alteration, injection, and effusion processes of sand extrudites. Injection was triggered by residual volcanic heat and possibly earthquakes.