Geochemistry and source characteristics of Dehsard mafic volcanic rocks in the southeast of the Sanandaj–Sirjan zone, Iran: implications for the evolution of the Neo-Tethys Ocean

The Late Jurassic-Early Cretaceous Dehsard mafic volcanic rocks crop out in the southeastern Sanandaj-Sirjan Zone (SSZ),composed primarily of basalts and basaltic andesite with subordinate dolerite. They are influenced to some degree by hydrothermalalteration under zeolite-greenschist facies. Using fairly immobile trace elements, the mafic volcanic rocks show subalkaline (tholeiitic)affinities. They commonly have similar designs with somewhat strong enrichment in light rare earth elements (LREEs) and large ionlithophile elements (LILEs) and depletion in high field strength elements (HFSEs; e.g., Nb, Ta, Ti) and nearly flat heavy rare earthelement (HREE) patterns. The negligible or absence of negative Eu anomalies indicate that plagioclase played an insignificant roleduring magma evolution. The low La/Nb (1.03-2.31) and Nb/Y (0.12-0.46) ratios, relatively high Zr/Y (4.03-8.18) and Th/Ta (2.25-9.64) ratios, steady enhanced normalized patterns, and moderate La/Nb ratios hint at an island arc and most likely a back-arc basinenvironment for the formation of Dehsard mafic volcanic rocks. The arc magma resulted from partial melting of depleted mantle sourcethat experienced assimilation and fractional crystallization and was enhanced by melts of subducted sediments or contribution of slabderivedfluids in an intraoceanic subduction environment in the Neo-Tethyan Ocean. Therefore, the presence of an island arc setting(Dehsard island arc) must be investigated in the south of the SSZ prior to the Late Jurassic-Early Cretaceous as the Neo-Tethys oceaniccrust was subducting north beneath the southern margin of the Central Iranian Microcontinents. The later collision of the arc with SSZled to tectonic proximity of the Dehsard mafic volcanic rocks to SSZ components.