Evidence of mingling between contrasting magmas in the Ribeirão do Óleo Pluton, Coastal Terrane and the tectonic implications on the Ribeira Belt, Brazil

Gneiss–migmatitic rocks and granites between the Cubatao and Itariri shear zones characterize the Mongagua Complex-Coastal Terrane. Three major units are defined: (1) the Itariri Suite (IS) composed of monzogranites, granodiorites, tonalites, and locally gneiss–migmatitic rocks; (2) the Areado pluton composed of monzogranite and locally tonalite; and (3) the Ribeirao do Oleo Pluton mainly composed of monzogranites, which is the subject of this article. Combined field observations, petrography, Sr–Nd–Hf isotopes, U–Pb zircon data, and preliminary geochemical studies are presented for the Ribeirao do Oleo Pluton (ROP), intrusive in granite-gneisses of the IS. It is a plutonic association of weakly peraluminous, medium-to-high-K biotite monzogranites that surround microgranular intermediate enclaves, which are products of magma mingling. Different from the most examples of magma mingling described in the literature, the ROP mingling did not result from the intrusion of hot mafic magma into colder host felsic magma. Conversely, the emplacement of the monzogranite started most likely during the medium-to-final stage of crystallization of the quartz microdiorite. A detailed study of LA-ICP-MS U–Pb zircon ages, including zircon morphology and internal structure, was useful to determine more precisely the emplacement sequence and the relation between the units of the ROP. Intermediate and acid facies have Paleoproterozoic and Neoproterozoic inheritances, moreover a mixture of xenocrysts, antecrysts, and autocrysts, indicative of a complex evolution of the ROP. Several magma crystallization pulses are recorded at 655–624 Ma, 627–601 Ma, and 613–586 Ma. The negative eHf(t) ranging from − 17.26 to − 12.51 in monzogranites, eNd(t) values of − 10.66 to − 7.83 at t = 600 Ma in both facies, 87Sr/86Sr of ca. 0.708 for the monzogranite and 0.706 for the quartz microdiorite indicate a strong crustal contribution in the genesis of intermediate and acid magmas of this pluton.