Reworked old crust-derived shoshonitic magma: The Guarany pluton, Northeastern Brazil

Abstract The 572 Ma Guarany stock consists of magmatic epidote-bearing hornblende monzodiorite to biotite granite that intruded Paleoproterozoic orthogneisses about 10 km inland from the coast in northeastern Brazil. Co-magmatic diorite enclaves and dikes are abundant throughout the pluton. The monzodiorite–granite pluton and diorite enclaves are shoshonitic and display continuous trends in variation diagrams. They display chemical and isotopic characteristics of crustal melts, such as enrichment in incompatible elements, high back-calculated initial 87 Sr/ 86 Sr ratios (avg. 0.71253), negative eNd (0.57Ga) values (avg. − 14.58), as well as high and variable (+ 9.1 to + 11.1‰ VSMOW ) δ 18 O (zircon) values. Correlations between O-isotope and whole-rock silica contents, as well as initial 87 Sr/ 86 Sr ratios with 1/Sr concentrations, suggest hybridization of a lower continental crustal melt with more felsic crustal rocks, concomitant with fractional crystallization. Amphibole chemistry and whole rock Zr, TiO 2 and P 2 O 5 contents suggest magma solidification at a pressure ~ 7 kbar and near liquidus temperature ~ 900 °C. The parental magma was likely formed by partial melting of old (tDM = 2.0 Ga) amphibolitic lower continental crustal rocks, in a post-collisional setting, probably triggered by underplating of mantle-derived mafic magma during the period of relaxation after collision.