Overview of the geochemistry and Rb/Sr, Sm/Nd isotopes of Middle Jurassic and Tertiary granitoid intrusions: a new insight on tectono-magmatism and mineralization of this period in Iran

One of the most intensive occurrences of magmatism in Iran was in the middle Jurassic period. Among the granitoid intrusions in this period as discrete bodies or complexes can be pointed to Aligoodarz, Alvand, Astaneh, Boroujerd, Malayer, and Chah-Dozdan in the Sanandaj-Sirjan zone; Shir-kuh and Ayrakan in the Central Iran zone; Shah-kuh, Sorkh-kuh and Kalateh-Ahani in the Lut Block. These granitoids are mostly peraluminous and belong to high-K calc-alkaline series. CaO/Na2O ratios (0.12 to 8.37) mostly suggest a clay-free source for formation of the intrusive rocks magma. Chondrite-normalized Rare Earth Elements (REEs) diagram do not display high enrichment of Light Rare Earth Elements (LREEs) than Heavy Rare Earth Elements (HREEs) and general pattern is relatively flat. In addition, diagram shows Eu negative anomaly, which can be attributed to indicate reducing conditions in formation of magma and/or magma derived from plagioclase depth as source. The lower continental crust-normalized spider diagram indicates enrichment in LILE (Rb, Cs, and K) and LREE (La and Ce) and depletion in Ba, Nb, Ta, Sr, and Ti. Initial 87Sr/86Sr ratios are 0.70609 to 0.71938 and initial εNd values are negative (from -6.51 to -1.1) indicating that magma derived from continental crust. Geochemical and isotopic evidence of the intrusive rocks shows continental crust origin (S-type granitoid) and due to continental collision. Geological findings such as stop in sedimentation, regional metamorphism, ophiolite displacement, and continental collision-related mineralization confirm continental collision between Iranian and Arabian plates in the Middle Jurassic period.