Shoshonitic magmatism in the Deh-Zahir area, southeast Iran: Evidence for post collisional magmatism and mantle metasomatism in the southeastern Urumieh-Dokhtar magmatic arc

Abstract

In the northern part of the Dehaj-Sarduieh volcano-plutonic belt (Deh-Zahir area, Kerman province, Iran), a series of subvolcanic rocks occur as dykes. These dykes show variable porphyritic textures and contain large plagioclase, clinopyroxene, K-feldspar and occasionally altered olivine phenocrysts set in an intergranular and trachytic textured groundmass. The groundmass consists of olivine, clinopyroxene, plagioclase, K-feldspar, analcime and opaque crystals. Electron microprobe analyses reveal that the plagioclases are mainly bytownite, K-feldspars are sanidine and pyroxenes are diopside and salite. Based on geochemical data, these rocks are classified as trachy-basalts with shoshonitic affinity, with primitive mantle-normalized spider diagrams showing clear depletions in Nb, Ti, and heavy rare earth elements (HREE) + Y and a strong enrichment in large-ion lithophile elements (LILE). Chondrite-normalized REE diagrams for these rocks show light REE enrichment, but heavy REE + Y are less, without any remarkable Eu anomaly. Primitive 87Sr/86Sr ratios and positive εNd values for the studied dykes change from 0.70438 to 0.70550 and 2.09 to 5.76, respectively, of which these were derived from parental magma extracted from partial melting of metasomatized mantle, namely spinel peridotite. However minor contamination with upper crust was also involved in the composition of the studied dykes. Tectonomagmatic discrimination diagrams and zircon U-Pb age data show that the Deh-Zahir dykes formed after collision of the Arabian and Eurasian plates in the Miocene.