Alkaline magmatism in the Ponta Grossa Arch, SE Brazil: A review

The southern side of the Ponta Grossa Arch (PGA), a prominent NW-SE-trending tectonic feature extending over 600 km, was the site of important alkaline and alkaline-carbonatitic magmatic activity in Early and Late Cretaceous times. Occurrences associated with two of their lineaments (Guapiara and Sao Jeronimo-Curiuva) are quite variable in composition and include the following rock associations: ultramafic-mafic, syenitic, carbonatitic, fine-grained rocks (dikes), and fenites. Except for Tunas complex and some more evolved dikes outcropping in the area of Cerro Azul, which show sodic composition, the remaining rocks are clearly of potassic affinity. Crystal fractionation and accumulation processes played a major role in the formation and evolution of the PGA rocks, whereas crustal contamination or AFC seems to be restricted to the Cananeia lithotypes and a few dikes associated with the Juquia and Tunas complexes. Furthermore, liquid immiscibility from silicate magmas is believed to be responsible for the formation of carbonatites in mostly alkaline and alkaline-carbonatitic complexes. The silicate rocks generally have higher Sri and lower Nd(i), lying mainly in the enriched quadrant. Similar isotopic signatures are displayed by the associated carbonatites. Tom model ages indicate that the PGA alkaline magmatism appears to be related to a lithospheric mantle source that suffered important metasomatic events, leading to its enrichment by incompatible elements and H-C-F-rich fluids. (C) 2011 Elsevier Ltd. All rights reserved.