Petrography, geochemistry and genesis of Alut plutonic complex, NW Saqez

The Alut granitoid complex is located in the northwestern part of the Sanandaj–Sirjan zone. This complex comprises three main units i. e. monzogranite to granodiorite bodies (SiO2 = 65–77 wt %) which is widespread throughout the area، a quartz-diorite to tonalite unit (SiO2 = 52–63 wt %) exposed as two stocks and mylonitic granitoid scattered as separate outcrops through the area. NE-SW trending microquartz-diorite and NW-SE trending aplite dykes are also present in this complex. The quartz-diorite to tonalite unit has relatively high CaO،FeO، MgO، Al2O3 and low Rb/Sr، Sr/Y، and (La/Yb) N، which preclude an origin of variably fractionated mantle melts and favour a mafic lower crustal source. Dehydration melting of biotite-bearing metasedimentary sources at relatively low pressures is proposed for the origin of monzogranite to granodiorite unit. Geochemically this complex is metaluminous to slightly peraluminous، typical of I-type granites. It belongs to low K (and high K for some monzogranite samples) calc-alkaline series and displays the geochemical characteristics typical of volcanic arc plutons related to an active continental margin area (e. g. significant Nb، Ti، P and Sr depletion). Based on collected geochemical data، the Alut granitoids originated by partial melting of crustal protoliths having different compositions in a deformed active margin.