Early post-collisional Brasiliano magmatism in Botuverل region, Santa Catarina, southern Brazil: Evidence from petrology, geochemistry, isotope geology and geochronology of the diabase and lamprophyre dikes

The post-collisional magmatism related to Brasiliano orogeny represented the final stage of the Dom Feliciano Belt in Rio Grande do Sul and Santa Catarina states, southern Brazil, presenting high-K calc-alkaline to shoshonitic and alkaline chemical signatures. Magmatic episodes related to this early period were found in Botuverá region, Santa Catarina state, represented by diabase and lamprophyre (spessartite-type) dikes intrusive in metavolcano–sedimentary rocks of the Brusque Metamorphic Complex (CMB). These dikes have massive structure and igneous textures ranging from very fine equigranular to porphyritic, and the latter is characterized by the presence of phenocrysts of plagioclase and hornblende. The dikes have northeast direction and sharp contacts with the metamorphic rocks, indicating that its position was after the main orogenic regional metamorphism that affected the CMB, interpreted as of collisional nature. The diabase has a basic composition, whereas spessartite lamprophyres are intermediate, with geochemical affinities to the tholeiitic series, with a significant enrichment in light rare-earth elements (LREE) and large ion lithophile elements (LILE) such as Cs, Rb, Ba, K and Sr, and negative anomalies for high-field-strength elements (HFS) such as Nb, Ta, U and T. The concentration of standard trace elements and the Th/Yb and Ta/Yb ratios indicate that these magmas were derived from an enriched mantle source and were strongly contaminated by crust. Except for higher values of K, these features are similar to those found in basaltic volcanic rocks associated with the post-collisional period in south Brazil. The widely dispersed values of ɛND (618), ranging between −13.74 and +5.52, highlights the heterogeneity of the source and reinforces the importance of a crustal component in the generation of these rocks. The extremely low value of εNd (618), of −21.67 obtained for spessartite lamprophyres supports the importance of the involvement of crust in the genesis of this rock. Using the U–Pb and LA–ICP–MS method, a concordant age of 618 ± 8.7 Ma was obtained in zircon crystals of a diabase dike of the region of Barra do Areia, in Botuverá, SC. The existence of inherited zircon grains older than 1800 Ma in this sample supports the involvement of Paleoproterozoic continental crust. The data analysis characterizes the first magmatic age related to the post-collisional period of the Brasiliano orogeny in this region of the Santa Catarina Shield.