File:Bebedourite (Serra Negra-Salitre Complex, Late Cretaceous, 83-84 Ma; NNE of Araxa, Minas Gerais State, Brazil) 1 (14817797608).jpg

Bebedourite from the Cretaceous of Brazil. (6.3 centimeters across at its widest)

Bebedourite is a scarce, ultramafic intrusive igneous rock. It’s actually a pyroxenite (>90% pyroxene) that is overwhelmingly dominated by diopside clinopyroxene (CaMgSi2O6), plus a significant alkaline content. So, an alternate rock name would be alkaline clinopyroxenite. Other minerals reported from this bebedourite are phlogopite mica, magnetite, perovskite, apatite, calcite, and ilmenite.

The sample comes from the type locality of bebedourite: a ring of pyroxenites surrounding the carbonatite core of the Serra Negra-Salitre Complex in southeastern Brazil. Published isotopic dates show that the Serra Negra-Salitre Complex is 83 to 84 million years old (mid-Late Cretaceous). The complex is part of the Alto Paranaíba Igneous Province, which consists of about two-dozen igneous intrusions between Brazil’s São Francisco Craton and the Paraná Basin. These igneous bodies have unusually alkaline-rich chemistries, resulting in the presence of rare rocks. They date to between 80 and 90 million years (Late Cretaceous). The intrusions appear to have been generated by hotspot (mantle plume) activity underneath the South American continental lithosphere (see Gibson et al., 1995). The Trinidade-Martin Vaz Hotspot has been identified as the culprit - it is now located in the western parts of the South Atlantic Ocean.

Geologic unit and age: Serra Negra-Salitre Complex (also known as the Serra Negra-Salitre Carbonatite Complex; Serra Negra-Salitre Alkaline Igneous Complex; Serra Negra-Salitre Massif), Alto Paranaíba Igneous Province, mid-Late Cretaceous, 83-84 Ma

Locality: north-northeast of Araxá, western Minas Gerais State, southeastern Brazil.

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