Mineral chemistry and Ti in zircon thermometry: Insights into magmatic evolution of the Sangan igneous rocks, NE Iran

The Sangan Magmatic complex (SMC) is, a large I-type magmatic complex, located in the northeastern Iran. Zircons extracted from the intrusive and volcanic rocks within the SMC record a similar Hf compositions and REE patterns, indicating that these chemical signatures have likely been inherited from the same source and simple history of magmatic crystallization during the evolution of the orogeny. The zircon from volcanic rocks yield Ti-in-zircon crystallization temperatures of 667-1145 °C with average temperatures of 934 °C while those from granitoids indicate crystallization temperatures of 614-898 °C with an average of 812 °C. Ti-in-zircon, Ti in biotite thermometries also indicates that the crystallization temperatures of volcanic rocks are relatively higher than those of granitoids. The biotite chemistry studies reveal that this mineral crystallized at approximately 725°-800 °C and 758° to 816 °C for granitoid and volcanic rocks, respectively, which is similar to obtained temperatures by Zir-saturation of Eq. (1). Tzicsat and Tmagma trend lines on the T-SiO2 diagram cross at high silica contents of ∼68 wt.%, at which temperature the magma becomes zircon-saturated and new zircons are crystallized. The zircon REE data including Ce/Ce*, Eu/Eu*, and Th/U ratios suggest that SMC igneous rocks are formed from oxidized magma. However, the zircon Th/U and Hf data suggest that the SMC became progressively more oxidized and also indicate lower temperatures from volcanic and plutonic rock with decreasing time.