Zircon U-Pb dating, geochemistry and evolution of the Late Eocene Saveh magmatic complex, central Iran: Partial melts of sub-continental lithospheric mantle and magmatic differentiation

The Saveh magmatic complex is a composite intrusion of diorite to tonalite. It is part of the Urumieh-Dokhtar magmatic arc in central Iran. Zircon U-Pb dating indicates that emplacement and cooling occurred 37-40 Ma ago in late Eocene (Bartonian) time. Saveh igneous rocks define a continuous mafic-felsic continuum in terms of SiO2 (55.4-70.8 wt%), Al2O3 (142-19.8 wt%) and CaO (6.4-17.1 wt%) contents. The initial values of Sr-87/Sr-86 and epsilon(ND)(t) are 0.7048 to 0.7062 and + 2.6 to + 3.4 (Mean = +2.9). Nd model ages (T-DM = 555 to 616 Ma) are consistent with derivation from Iranian continental crust and subcontinental lithospheric mantle of Cadomian age (500-600 Ma). Saveh igneous rocks are enriched in K, Cs and Pb and depleted in P, Nb and Ta, indicating that the magma source was moderately affected by slab-derived fluids, as expected for the Eocene tectonic environment. The continuum of rock types from diorite to graphic eutectic tonalite indicates that magmatic evolution was controlled by the F (FeO + MgO + MnO)-Anorthite (An)-Orthoclase (Or) cotectic with minor contamination by supra-crustal components. Similar initial ratios of Sr-87/Sr-86 and Nd-143/Nd-144 for all of the rocks and the slightly younger age of tonalitic rocks (2-3 Ma younger) further indicate that the crystallization of quartz and plagioclase with graphic texture occurred in the final stage of magmatic differentiation. Saveh magmas reflected partial melting of Iranian subcontinental lithospheric mantle due to extension above the Neo-Tethys subduction zone. (C) 2018 Elsevier B.V. All rights reserved.