Petrology, Geochemistry and Tectonomagmatic Setting of the Silijerd Intrusion, Northwest Saveh

Silijerd intrusion with an age of Late Eocene - Oligocene (39.2 3.2 Ma) is located in Uromeyeh-Dokhtar magmatic arc, central Iran structural zone, northwest Saveh. This intrusion is composed of a continuous compositional range including: diorite/gabbro, granodiorite, syeno-monzogranite and alkali granite intruded into the Eocene volcanic and pyroclastic rocks. Variation diagrams showing trends of major and trace elements indicate a continuous compositional range and a comagmatic origin for these rocks. Trends of compatible- incompatible elements indicate the important role of fractional crystallization in the genesis of these rocks. All samples are metaluminous with medium-high K with calc-alkaline nature. High values of Rb, Sr, K, U, Th, Zr and Ba and high ratios of K2O/Rb and FeO/MgO indicate the similarity of the rocks of this intrusion with the rocks of continental margin magmatic arc intrusions. Depletion in Nb,P,Ta and Ti and enrichment in K,Sr,Rb,Cs and Ba are obvious in the spider diagrams of these samples. The enrichment in LILE and depletion in HFSE reveal the I-type metaluminous magmatism of volcanic arcs (VGA). Whole rock 87Sr/86Sr ratios of this intrusion range from 0.704759 to 0.705166 and it can be correlated with the values of these ratios in the mantle and lower crust sources and low contamination of their magmas with upper crust. Existence of K-feldspar megacrysts and mafic microgranitoid inclusions in this intrusion, high abundances of La and Ce, V enrichement in mafic terms and low whole rock 87Sr/86Sr ratios of this body, suggested a partial melting of mantle wedge, subducted oceanic crust (metabasaltic sources) or lower continental crust (metatonalitic sources) origins for it. The discrimination tectonic setting diagrams also indicate an I-type continental volcanic arc magmatism for this intrusion.