Abstract Lateral escape tectonics mediated by strike-slip fault zones are an efficient mechanism of rock deformation in the continental crust of collision zones. The Borborema shear zone system, which shows dimensions comparable to the Cenozoic extrusion of Indochina, defines a lateral escape setting of the Brasilano orogeny in Northeastern Brazil. In this paper, the timing of high-grade metamorphism and compositions of the terranes involved in the shear deformation were investigated. The Patos shear corridor deforms the Siderian to Neoarchean rocks of the Granjeiro Complex that, in turn, form the basement of Seridó-Lavras da Mangabeira metapelites. U-Pb zircon ages and Sm-Nd whole-rock isotopic compositions indicate that the 2.80 – 2.35 Ga basement sequences mainly include juvenile material, whereas zircons from synkinematic migmatites indicate that the partial melting occurred in the Late Ediacaran (ca. 565 Ma). Cooling rates provided by 40Ar/39Ar range from 12 to 17°C/Ma, indicating a differential shear zone exhumation, in agreement with a transpressive setting. The presence of allochthonous Siderian sequences dismembered along the shear zone suggests that the Seridó-Granjeiro corridor defines a major tectonic boundary connected to the collisional front defined by the convergence of São Francisco-Congo and Amazonian cratons.

ABSTRACT: Three series of alkaline dikes are characterized in a restricted area of the Mantiqueira Range: a weakly silica-undersaturated series (normative ne < 7), of potassic character, represented by basanite, tephrites, alkali basalts, basaltic trachyandesites, phonotephrites, tephriphonolites, and trachyandesites, an intermediate series (7 > normative ne > 13), of potassic character, consisting only of basanites and tephrites, and a strongly silica-undersaturated series (normative ne > 13), of sodic character, consisting of basanites, tephrites, phonotephrites, and phonolites. Ar-Ar data for biotite from a tephriphonolite dike yielded an average age of 85.4±0.4 Ma. All three series show similar evolution trends controlled mainly by early-fractionation of olivine, spinel and clinopyroxene and, secondly, fractionation of plagioclase and apatite. Different degrees of crustal assimilation are suggested for each series. Assimilation processes are responsible for the wide 87 Sr/ 86 Sr i (0.70447-0.71172) and 143 Nd/ 144 Nd i (0.51237-0.51244) ranges, for the increased K 2 O/Na 2 O, Ba/Sr and Rb/Sr ratios, and for the reduced Ce/Pb ratios. In general, a significant contribution from partially melted host rocks is associated to the weakly silica-undersaturated potassic series. A phlogopite-bearing carbonate-metasomatized heterogeneous peridotite source accounts for the main chemical variations in the least contaminated samples of each series. Geochemical signatures of the strongly sodic alkaline series indicate a greater contribution from carbonated pyroxene-rich veins in the mantle source.