Paleoproterozoic accretionary and collisional processes and the build-up of the Borborema Province (NE Brazil): Geochronological and geochemical evidence from the Central Domain

Abstract

Several Brasiliano-Pan-African belts consist of large areas of reworked Paleoproterozoic rocks. Characterization of these rocks is needed to place better controls on Precambrian paleogeographic reconstructions. The Borborema Province, northeastern Brazil, occupies a central position in West Gondwana configuration, and knowledge of its geological evolution is crucial to infer relationships between Paleoproterozoic units in South America and Africa. Here, we report U–Pb ages, major- and trace-elements analyses and Sm–Nd isotopic data for orthogneisses in the eastern portion of Central Domain. The dominant basement units in the study area are banded gneisses of intermediate composition and relatively juvenile character, and migmatitic gneisses of granitic composition with Archean Nd TDM model ages. One sample of the banded gneiss yielded a weighted 207Pb/206Pb age of 2096 ± 23 Ma and an upper intercept age of 2044 ± 27 Ma, which we interpret, respectively, as ages of crystallization and metamorphism. Two large units of migmatitic gneiss in the southern and central parts of the area gave ages of, respectively, 2057 ± 20 Ma and 2055 ± 23 Ma; an orthoamphibolite associated with the latter yielded crystallization age of 2042 ± 11 Ma and metamorphic age of 1996 ± 13 Ma. All these rocks have geochemical signatures typical of subduction zone-related magmas. Combined with evidence provided by previous studies, we suggest that the evolution of the study area starts with island arc construction around 2.2 Ga, leading to an expressive volcanic arc edifice by 2.13–2.10 Ga. By 2.06 Ga, the crust had evolved enough to become intruded by magmas formed at the mantle wedge of the now largely continental magmatic arc, which continued to be intruded by mantle melts until at least 2.04 Ga. An augen gneiss in the northern part of the area, with an age of 2109 ± 15 Ma, and a migmatitic gneiss with a much older age (2183 ± 9 Ma), both of which have geochemical characteristics akin to intraplate magmas, suggest that crustal reworking also took place. The 1981 ± 23 Ma age of a small body of peraluminous felsic gneiss may be related to regional metamorphism and syncollisional magmatism at c. 2.0–1.98 Ga.