Zircon U–Pb ages and Sr-Nd isotope ratios for the mafic microgranular enclaves in the sirstan cretaceous granitoids, NE Iraq: Evidence of cogenetic magmatic origin

Mafic microgranular enclaves (MMEs) are observed in the Sirstan granitoid (SG) body in the Shalair Valley area, northeastern Iraq, within the Zagros Orogenic Belt. Zircon U–Pb ages for the MMEs are 110 Ma with an I-type affinity closely resembling the enclosing rocks. The MMEs are gabbroic-diorite to diorite in composition, and the main mineral assemblage are plagioclase, hornblende, and K-feldspar. The MMEs are intermediate in composition and have low SiO₂ (52.0–60.2 wt%) and high Fe₂O₃, Al₂O₃, TiO₂ and CaO contents (Fe₂O₃ = 8.7–13.3 wt%; Al₂O₃ = 14.8–17.2 wt%; TiO₂ = 0.71–1.02 wt%; CaO = 3.4–11.4 wt%). The enclaves have analogous Sr and Nd isotope compositions with positive εNd_(t) values (⁸⁷Sr/⁸⁶Sr(i) = 0.7047 to 0.7058; εNd_(t) = +2.0 to +2.5) as their host granitoids (⁸⁷Sr/⁸⁶Sr(i) = 0.7044 to 0.7057; εNd_(t) = +0.1 to +2.7). The uniform REE patterns and the fractionation trends of major and trace elements of the MMEs with their host rocks indicate simultaneous crystallization by fractionation from the same magma source. According to the geochemical aspects of the MMEs and their host SG rocks with young T_DM ages (676–720 Ma), the low ratios of the Rb/Sr and Nb/Y ratios, in addition to the same ages and Sr-Nd isotope ratios, infer that the same source magma was derived from a young depleted mantle without the contribution of ancient crustal components.