Chemical, mineralogical and Sr, Nd, C and O isotopes constraints on the origin of the rocks of the Araxá alkaline-carbonatite complex (Brazil), and proposal of an evolution model

This work aims to understand the genesis of the Araxá carbonatite complex (Brazil). The complex core contains Nb-rich magnetite phlogopitite and metamorphosed phoscorites intersected by veins of Sr-rich norsethite carbonatites. It is surrounded by an internal ring of Ba- and Sr-rich carbonatites mineralized with phosphate, and an edge ring of barren calcite carbonatites. The 87 Sr/ 86 Sr ratios vary between 0.704683 of the calcite-carbonatites ring and 0.705401 in carbonatites of the core, and the 144 Nd/ 143 Nd ratios vary between 0.512194 ( Є Nd (0) = -8.66) and 0.512389 ( Є Nd (0) = -4.84) respectively. The correlation between δ 18 O SMOW (ranging from 8.21 to 15.88‰) and δ 13 C PDB (ranging from -8.03 to -4.74‰) values, as well as between δ 18 O SMOW and 143 Nd/ 144 Nd (t) values, indicate that the core phlogopitites and the core’s phoscorites together with the carbonatites of the ring were formed following distinct lines of evolution. Multielement diagrams along with rare earth element patterns, 87 Sr/ 86 Sr and 144 Nd/ 143 Nd ratios, and C and O isotope data, indicate that all Araxá rocks were derived simultaneously from the same place in the mantle. Magmas that formed Araxá are not genetically related to continental basalt flows of the Paraná Basin, located next to the complex. A multi-stage magmatic system consistent with the assimilation–fractional crystallization–liquid immiscibility acting on multiple batches of variously contaminated carbonated-silicate parental melt may produce the variation in the values of the Sr and Nd isotopic ratios. Phlogopitic magma is in equilibrium and could have resulted from the melting of metassome mica – amphibole – rutile – ilmenite - diopside (MARID) lithospheric mantle.