Late Cryogenian–Ediacaran magmatism in southern Borborema Province, NE Brazil: Ages, sources, petrogenesis, and tectonic setting

The Sergipano Orogenic System (SOS) in southern Borborema Province (NE Brazil) hosts voluminous Neoproterozoic plutonism related to the Brasiliano/Pan-African Orogeny. This paper presents comprehensive whole-rock geochemical data, titanite U-Pb ages, and the first combined zircon U-Pb and Lu-Hf isotope results for plutonic rocks from the Macururé Domain to constrain their sources, petrogenesis, and tectonic setting. Three magmatic episodes are recognized and record the evolutionary stages of the orogen. (ⅰ) Early-collisional magmatism (643–628 Ma) comprises gabbros and diorites with minor tonalites characterized by well-developed tectonic foliation and evidence of solid-state deformation. These rocks are magnesian, high-K calc-alkaline, LILE- and LREE-enriched and provide subchondritic ε_Hf(t) values (−6.5 to −4.7) and Orosirian Hf-T_DM^C model ages (1.83–1.94 Ga). Such features indicate derivation from a lithospheric mantle source metasomatized by incorporating crustal components through subduction processes prior to magma generation, possibly related to the Rhyacian Orogeny (2.20–1.96 Ga). Extensive mixing/mingling between basaltic and crust-derived magmas took place at lower crustal depths, producing coeval hybrid diorites and quartz-diorites. (ⅱ) Syn-collisional magmatism (630–624 Ma) encompasses biotite- and muscovite-bearing granodiorites and monzogranites, preserving their structures parallel to the schistosity of the country rocks. These rocks are leucocratic, weakly metaluminous to peraluminous, and contain abundant surmicaceous enclaves. Petrographic features and geochemical composition suggest an origin related to the partial melting of graywacke protoliths with a subordinate igneous component. (ⅲ) Late-collisional magmatism (625–600 Ma) includes undeformed and isotropic monzonites and granodiorites, which truncate the regional foliation. These rocks are consistently metaluminous and magnesian, showing affinities with the high-K calc-alkaline to shoshonite series. Trace element modeling with subchondritic ε_Hf(t) values (−8.3 to −4.1) and Paleoproterozoic Hf-T_DM^C model ages (1.77–2.03 Ga) demonstrate that reworking of ancient lower mafic crust played an important role at this time. The integration of our data with previously published results leads us to conclude that the geodynamic evolution of the SOS along the western Gondwana margin is better explained by large-scale lithospheric extension followed by basin inversion and continental collision.