Ediacaran post-collisional K-rich granitic magmatism within the Major Gercino Shear Zone, Southern Brazil: An example of prolonged magmatism and differentiation under active transcurrent tectonism

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The post-collisional period of the Brasiliano/Pan-African Orogenic Cycle along the Dom Feliciano Belt in southern Brazil (650–580 Ma) is marked by intense magmatism, comprised of substantial volumes of coeval granitic and mafic rocks emplaced along transcurrent shear zones that constitute the Southern Brazilian Shear Belt. Some representatives of this magmatism are the Estaleiro Granodiorite (EG) and associated fine-grained granites that compose the Estaleiro Granitic Complex (EGC), together with minor volumes of mafic material as enclaves and tabular bodies. The EGC is a syntectonic rock association that registers the main transcurrent phase of the Major Gercino Shear Zone (MGSZ). The Estaleiro Granodiorite and fine-grained granites share the same MGSZ dextral transcurrent kinematics and evolution from magmatic to solid-state conditions under deformational temperatures consistent with upper-greenschist to mid-amphibolite facies. New zircon UPb LA-MC-ICP-MS crystallisation ages, 612 ± 3.5 and 611 ± 5.3 Ma, for the Estaleiro Granodiorite undeformed and deformed portions constrain the timing of transcurrent tectonic activity of the Major Gercino Shear Zone. Geochemical features as SiO2 contents above 63%, the alkaline and potassic predominant character [K2O > (Na2O – 2)], enrichment in Na2O + K2O (6.9–9.2 wt%), high K2O/Na2O ratios (0.8–1.4), high Al2O3 (14.1–16.4 wt%), low TiO2 (0.1–0.8 wt%) and high Fe2O3/FeO (~1.11), Ba (488–1701 ppm),Sr (260–1006 ppm), strong enrichment in LILE relative to HFSE, REE with moderate fractionation [(La/Yb)N = 10.6–51.1] and absence of strong Eu negative anomalies [(Eu/Eu*)N = 0.54–1.23] of the Estaleiro Granitic Complex granitoids are compatible with rocks of shoshonitic affinity. New 87Sr/86Sri ratios and ƐNdt values obtained for fine-grained granites point to increasing crustal contamination along the differentiation of the complex. Whole-rock chemical and SrNd isotope data point to mantle sources modified by previous, subduction-related metasomatism. The primary magmas have evolved through AFC processes, more prominent in the most differentiated and/or deformed rocks. We suggest that the transcurrent tectonism of the Major Gercino Shear Zone played an important role in the activation of mantle sources capable of originating shoshonitic magmas and facilitated their interaction with crustal melts to generate the Estaleiro Granitic Complex granitoids.