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

Authors : Mohammadali NAZEMEI, Mohsen ARVIN, Sara DARGAHI

Pages : 249-268

View : 18 | Download : 9

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :  The Late Jurassic-Early Cretaceous Dehsard mafic volcanic rocks crop out in the southeastern Sanandaj-Sirjan Zone insert ignore into journalissuearticles values(SSZ);, composed primarily of basalts and basaltic andesite with subordinate dolerite. They are influenced to some degree by hydrothermal alteration under zeolite-greenschist facies. Using fairly immobile trace elements, the mafic volcanic rocks show subalkaline insert ignore into journalissuearticles values(tholeiitic); affinities. They commonly have similar designs with somewhat strong enrichment in light rare earth elements insert ignore into journalissuearticles values(LREEs); and large ion lithophile elements insert ignore into journalissuearticles values(LILEs); and depletion in high field strength elements insert ignore into journalissuearticles values(HFSEs; e.g., Nb, Ta, Ti); and nearly flat heavy rare earth element insert ignore into journalissuearticles values(HREE); patterns. The negligible or absence of negative Eu anomalies indicate that plagioclase played an insignificant role during magma evolution. The low La/Nb insert ignore into journalissuearticles values(1.03-2.31); and Nb/Y insert ignore into journalissuearticles values(0.12-0.46); ratios, relatively high Zr/Y insert ignore into journalissuearticles values(4.03-8.18); and Th/Ta insert ignore into journalissuearticles values(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 basin environment for the formation of Dehsard mafic volcanic rocks. The arc magma resulted from partial melting of depleted mantle source that experienced assimilation and fractional crystallization and was enhanced by melts of subducted sediments or contribution of slabderived fluids in an intraoceanic subduction environment in the Neo-Tethyan Ocean. Therefore, the presence of an island arc setting insert ignore into journalissuearticles values(Dehsard island arc); must be investigated in the south of the SSZ prior to the Late Jurassic-Early Cretaceous as the Neo-Tethys oceanic crust was subducting north beneath the southern margin of the Central Iranian Microcontinents. The later collision of the arc with SSZ led to tectonic proximity of the Dehsard mafic volcanic rocks to SSZ components.
Keywords : Volcanic rocks, subduction, SanandajSirjan zone, back arc basin, Neo Tethys, petrogenesis