Post-collisional Plio-Pleistocene Anar-Dehaj adakitic subvolcanic domes in the central volcanic belt of Iran: geochemical characteristics and tectonic implications

In the area betweenAnar and Dehaj, located in the Urumieh-Dolchtar magmatic assemblage (UDMA), there are some Plio-Pleistocenic subvolcanic porphyritic andesitic-dacitic domes. The subvolcanic domes, as a part of Dehaj-Sarduieh belt in Kerman province, show tafoni erosion and magma mingling evidences. Petrographically, the domes are andesite and trachyandesite in composition and are characterized by microliticporphyritic, glomeroporphyritic, trachytic and aphanitic textures. Mineralogically, the domes consist of plagioclase, amphibole, clinopyroxene and opaque minerals. Geochemical studies reveal that Anar-Dehaj subvolcanic domes can be divided two groups, named group 1 and group 2, on the basis of the silica content. Group 1 shows high-K calc-alkaline andesite-trachyandesite composition; whereas group 2 is medium-K calc-alkaline dacite. The absence of a distinct Eu anomaly in all samples suggests contemporaneous crystallization of plagioclase and amphibole, and/or oxidation state of magma. Trace element discrimination diagrams along with chondrite-normalized rare earth element patterns show that the Anar-Dehaj subvolcanic rocks formed in a subduction related environment. Moreover, high Sr/Y and La/Yb ratios along with low Y and HREE contents are consistent with adakitic natures. It is suggested that the AnarDehaj subvolcanic domes formed in a post-collisional setting due to slab melting or underplating of basaltic magmas under thick Plio-Pleistocene continental crust.