The Serra Negra do Norte area belongs to the geographic domain of Seridó, located in the Northeastern folding region, consisting of orthogneisses, probably from the Lower Proterozoic. These rocks have a granitic and quartz-monzonitic composition and comprise an association predominantly of augen gneisses, housed in the gneisses of the Caicó Group, belonging to the Archean basement, and in the supracrustal metasediments, represented in the area by the Jucurutu Unit, which is the base of the Seridó Group. Cutting through the orthogneisses and metasediments, an Intrusive Suite occurs, related to the tectonic events of the Brasiliano cycle, composed of three distinct temporal placement units and represented by granites, granodiorites, quartz-monzonites, quartz-monzodiorites and quartz-diorites. Three deformational events are recorded in the Serra Negra do Norte area. The oldest, dating back to the Trans-Amazonian cycle, affected both the cover sediments and the intrusion that metamorphosed into the heights of the gneisses. In the rocks of the Intrusive Suite, whose geological evolution culminated with the end of the Brasiliano cycle, the last two deformational events are recorded, while in the peak gneisses only the effects corresponding to the last of these events were observed. The petrographic evidences and the geochemical behavior of the major elements and, mainly, of the traces support the idea that the metamorphism, related to the first deformational event, was of the allochemical type, and may have been responsible for the k-feldspatization of the pre-augen gneisses, whose intensity, although not fully known, was not enough, however, to completely eliminate some primary textural and chemical characteristics. ”. However, the behavior of some major elements and traces is not consistent with the generation of the several units of this suite through continuous processes of magmatic differentiation, although they have acted in each unit individually. On the other hand, based on comparisons made with rocks from similar geological provinces, a petrogenetic evolution is suggested for the rocks of Units 1 and 2 and those of the Southern Body of Unit 3, via partial melting processes, either from sources or from a single source, probably located in the lower crust and undergoing different degrees of partial melting. As for the North Body of Unit 3, an origin is also suggested by partial melting, from a material where the peak gneisses made an important contribution. Significantly, the rocks of the Serra Negra do Norte area reveal striking structural, stratigraphic and chemical similarities, with rocks from Proterozoic magmatic provinces of Nigeria, indicating that these areas underwent analogous evolutionary processes provided by the physical continuity that existed between them in pre- Mesozoic drift.
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