Geochemical systematics and U–Pb zircon age of the Vulvara anorthosite massif, Lapland granulite belt, Baltic shield: magmatic sources and metamorphic alteration of the rocks

ABSTRACT The Vulvara anorthosites occur among the rocks of intermediate composition, in contrast to most Lapland granulite belt (LGB) anorthosites, associated with mafic granulites. The U-Pb, Sm-Nd and REE geochemical data were used to compare Vulvara with other LGB anorthosites. The intrusion of the Vulvara massif occurred in the interval of 2100–1965 Ma. The first metamorphic processing took place 1947 ± 11 Ma ago under granulite facies. Postgranulite transformations occurred 1900–1850 Ma ago under amphibolite facies; earlier (1896 ± 15 Ma) and later (1852 ± 17 Ma, 1846 ± 16 Ma) thermal events were established. The Vulvara anorthosites, in comparison with other LGB anorthosites, are distinguished by a more acidic composition of plagioclase, a higher F number of rocks and mafic minerals, a higher content of SiO2, Na2O, K2O, Ba, Sr, Zr, Nb, Rb, and a lower content of CaO. The Sm-Nd and REE geochemistry suggest that there are three groups of LGB anorthosites, distinguished both by age and magma source.