The genetic link between kamafugite magmatism and alkaline–carbonatite complexes in the Late Cretaceous Alto Paranaíba Igneous Province, Central Brazil

Abstract

ABSTRACT The Late Cretaceous Mata da Corda Formation, located in the eastern part of the Alto Paranaíba Igneous Province (APIP), Central Brazil, is one of the few places on Earth where kamafugite melts reached the surface generating large volumes of lava, pyroclastic rocks and shallow intrusions over an area of 4,500 km2. The western part of the APIP, however, is dominated by hundreds of diatreme-like kamafugites and shallow kimberlite intrusions and by the occurrence of multi-stage alkaline-carbonatite complexes. These complexes feature silica-undersaturated K-rich alkaline rocks, such as aillikite, that closely resemble the mineralogy and geochemistry of kamafugite, albeit lacking feldspathoids. The spatial and temporal distribution of kamafugite and aillikite within the APIP suggests a connection between them. In addition, on a regional scale, airborne magnetic data show three highly magnetic dipole-like structures to the south of the Mata da Corda Formation of an undisclosed nature, which bear geophysical similar responses to the neighbouring alkaline-carbonatite complexes. Links between kamafugite and aillikite are evaluated by the following chemical and isotopic evidence: (1) kamafugite and aillikite compositions plot in the kamafugite field of Foley’s ultrapotassic rock classification; (2) similar CI chondrite-normalized REE distribution, with aillikite enriched up to 2 times in REE compared to kamafugite; (3) both lithologies share almost the same rock-forming minerals; and (4) similar 143Nd/144Nd(i) and 87Sr/86Sr(i) ratios for all the APIP alkaline-carbonatite rocks, indicating a common source from an enriched lithospheric mantle. Therefore, silica-undersaturated rocks from alkaline-carbonatite complexes display an evolved ultrapotassic affinity indicative of a genetic link.