Abstract
ABSTRACT In Large Igneous Provinces (LIPs), sills are a key component of the plumbing system responsible for magma transport through the crust where magma fractionation takes place. In this work, we investigate four dolerite sills related to the Paraná-Etendeka LIP from Cerro do Coronel region, southern Brazil. They are basaltic andesites composed of plagioclase, augite+pigenonite, Ti-magnetite, and rare olivine, divided into a high- and a low-MgO group. The former is more depleted in SiO2, alkalis, and trace elements, with lower FeOt/MgO ratios, higher Eu/Eu*(N), less radiogenic 87Sr/86Sr and more radiogenic 143Nd/144Nd. The composition of Cerro do Coronel dolerites resemble those of evolved rocks from Morungava Intrusions, the silica saturated tholeiite dykes in southern Brazil, and the Cuaró Dyke Swarm dolerites from Uruguay. They evolved by fractional crystallization from primitive Gramado-type basalts under FMQ-2 fO2 conditions at low pressures (<3 kbar) and underwent assimilation of variable upper and lower crust, representing shallow-depth equilibration of magmas sourced from deeper crustal levels. The studied sills share some geochemical features with the Vale do Sol Fm. lavas, although we cannot assume they have the same age, and are part of a major plumbing system related to the low-Ti magmas of the Paraná-Etendeka LIP.
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