Petrography and petrogenesis of intrusive rocks in the northeast of Nayband, East of Iran

The study area is located 50 km northeast of Nayband in the easternmost part of Yazd province. The area is a portion of the Tertiary volcanic-plutonic rocks in the west of the Lut block. The geology of the region includes latitic to trachyandesitic lavas، which are intruded by subvolcanic rocks with monzonitic، syenitic and granitic compositions. The texture of all the intrusive rocks is porphyric to glomeroporphic. Plagioclase، K-feldspar، biotite and quartz are the main minerals of biotite quartz monzonite porphyry، biotite syenite porphyry and biotite granite porphyry. Clinopyroxene، besides these minerals is present in biotite-pyroxene monzonite porphyry. Based on geochemical studies، the biotite-pyroxene monzonite porphyry shows metaluminous and shoshonitic nature. This rock belongs to the magnetite series (oxidized) granitoid and is allocated to I-type. The relative enrichment of LREE versus HREE and enrichment of LILE and HFSE impoverishment indicate magma formed in subduction zone. The magma exhibits low degree of partial melting (>0. 1 to <3) from a garnet-spinel lherzolite source، which is contaminated by continental crust. The biotite granite porphyry is peraluminous and ultrapotassic. The rock belongs to ilmenite series (reduced) granitoid and is related to S-type. Based on Nb، Yb، Rb، Y and Ta contents، the magma formed in syn-collisional tectonic setting. The granitic magma is generated by partial melting of continental crust and clay-poor sediments source. The relative enrichment of LREE and depletion of HREE، highly negative Eu anomaly and low ratios of (La/Yb) N and)Ce/Yb)N can be attributed to the presence of residual plagioclase in the source area. The intrusion of this rock into the monzonitic unit indicates a collision occurred after the Eocene in the west of Lut block in which access to accurate geochronological and radiogenic isotopes data is required.