Petrology and Mineral Chemistry of the Oligocene–Miocene Qazan Granitoids from Central Urumieh-Dokhtar Magmatic Arc, Iran: Implications for the Neo-Tethyan Subduction

AbstractThe Urumieh-Dokhtar Magmatic Arc (UDMA) appears as a nearly linear suite of magmatic rocks that extends from NW to SE Iran parallel with the orogenic suture of the Zagros Fold-Thrust belt. The Qazan granitoids formed along the central part of UDMA and span a wide range of felsic rocks, including granodiorite, quartz diorite, diorite, and monzogranite. Their common rock-forming minerals are mainly quartz, feldspar, amphibole, biotite and clinopyroxene. These granitoids contain abundant mafic microgranular enclaves (MME). Bulk-rock major and trace element compositions returned a relatively low SiO2 content (ca. 51–55 wt %) and high Mg# (ca. 40–50) for MME samples, potentially reflecting a mantle-derived origin. The granitoid host rocks are metaluminous (A/CNK = ca. 0.7–1) I-type rocks with arc-related calc-alkaline affinity. They yield higher SiO2 contents with a comparatively larger variation (ca. 57–66 wt %) and lower Mg# (ca. 35–48), consistent with derivation from partial melting of lower continental crust. Mixing of two contrasting mafic (sourced from an enriched subcontinental lithospheric mantle wedge) and felsic (derived from lower continental crust) melts in the Neo-Tethyan subduction-related oxidizing system has resulted in generation of Qazan granitoid melts. Thermometry of Qazan intrusive rocks indicates that the ascending melt was crystallized at 1200–1100°C in lithospheric mantle to lower continental crust.