Age, Geochemistry, and Emplacement of the ~40-Ma Baneh Granite-Appinite Complex in a Transpressional Tectonic Regime, Zagros Suture Zone, Northwest Iran

The Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U-Pb dating shows that granites crystallized 41-38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO₂ (62.4-77.0 wt%), low contents of TiO₂ (0.25 wt%), MgO (0.05-1.57 wt%), and Fe₂O₃ (0.40-4.06 wt%) and high contents of Na₂O + K₂O (approximate to 10 wt%). In contrast, appinites have low contents of SiO₂ (51.0-57.0 wt%) and K₂O (<2.1 wt%) and high Fe₂O₃ (6.4-9.35 wt%), MgO (2.0-9.9 wt%), and Mg number (Mg# = 35-76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (⁸⁷Sr/⁸⁶Sr)ᵢ and ε_{Nd(40 Ma)} in both groups are similar, from 0.7045 to 0.7061 and -1.2 to +2.6, except for a primitive gabbroic dike with ε_{Nd(40 Ma)}) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates.