PETROGENESIS MODEL FOR THE ORIGIN AND EVOLUTION OF CHENAR GRANITOID STOCK, NW OF KERMAN, IRAN: EVIDENCE FOR SUBDUCTION RELATED MAGMATISM

The lower to middle Miocene Chenar granitoid stock-a part of the Central Iranian volcanic belt- is intruded into the Eocene volcano-sedimentary complex in the northwestern part of Kerman in south-central Iran. The contact between these two rock units is marked by hornblende hornfels facies. The granitoid rocks are found in the epizone at subsolvous condition (i.e., under 3.8-4% water content, water pressure of 5.5 kbars at 780-800 C° and estimated water activity of 0.4 to 0.45)

The granitoid rocks show enrichment in LIL elements such as Rb, Ba, K and Ce and depletion in HFS elements such as Y, Nb and Zr. Geochemical data and various trace element discrimination diagrams indicate that the Chenar granitoid rocks have characteristics of meta-aluminous to slightly per-aluminous, high K, calc-alkaline, I-Cordolarian type granites of volcanic arc settings and are formed in an active continental margin environment and probably represent a part of Andean-type magmatic arc which formed in response to the subduction of Neotethys oceanic crust beneath Central Iran and are unrelated to rift settings. These rocks are probably formed as a result of partial melting of the subducted oceanic lithosphere and its overlying mantle in a subduction zone at a depth with 16-20 kbars pressure, where the melting of the protolith occurred either in the solid state or in a relatively low water environment.