PETROGENESIS AND ORIGIN OF THE CHENAR GRANITOID STOCK, NW OF KERMAN, IRAN: EVIDENCE OF NEOTETHYS SUBDUCTION RELATED ARC MAGMATISM

The lower to middle Miocene Chenar granitoid stock, a part of Central Iranian volcanic belt, is intruded into Eocene volcano-sedimentary complex in northwestern Kerman in south Central Iran. The Chenar granitoid stock consists mainly of coarse to medium grain granodiorite and monzogranite with subordinate tonalite and syenogranite. Alkali granites as aplitic veins and quartz dioritic dykes frequently cut through the granitoid stock. Enclaves of various types and sizes (andesitic and microgranular mafic, few meters to several centimeters wide) also occur near the margin. The granitoid rocks represent convergent margin magmas enriched in large ionic lithophile elements (LILE) such as Rb, Ba, K, Ce and depleted in high field strength elements (HFSE) such as Y, Nb and Zr. The REE patterns have relatively smooth LREE enriched chondrite normalized REE profiles with (La/Yb)n between 4.28 to 14.66. A lack of Eu anomalies along with a continuous increase in the slope of LREE profile from tonalite to syenogranite exhibit a relatively low fractionated chondrite normalized pattern [(La/Yb)n] and also involvement of plagioclase in the melting processes. Small negative Eu anomaly in alkali granite is an indication of more differentiated rock type [(La/Yb)n=42.78] in Chenar granitoid stock. Geochemical data, various trace element discriminant diagrams, common igneous microgranitoid enclaves, and ocean ridge granite normalized multi-element diagrams indicate that the Chenar granitoid stock has characteristics of metaluminous to slightly peraluminous, calc-alkaline, I-type granite of a volcanic arc settings and is formed in an active continental margin environment. In this model, a NE-dipping subduction zone of Neotethys could have accounted for the arc volcanism of the Central Iran where felsic, Andean-type magmatic arc volcanics and plutonics were formed. As a result of subduction mafic arc magmas with significant fluids were produced following the dehydration of oceanic crust and partial melting of mantle wedge which in turn provoke partial melting of considerably metasomatised and enriched subcontinental lithosphere, leading to generation of siliceous magma. Its low-pressure crystal fractionation gave rise to generation of hydrous calc-alkaline magmas, represented in part by Chenar granitoid stock.