Petrology, geochemistry and geotectonic environment of the Alvand Intrusive Complex, Hamedan, Iran

Abstract

The Alvand Intrusive Complex is located near Hamedan (Iran) and crops out over an area 400km2 intruding the Sanandaj-Sirjan plutono-metamorphic belt. The emplacement age of the AIC is constrained to Upper to Middle Jurassic, based on U–Pb zircon geochronogic data. This complex consists of granites (monzogranite and syenogranite), leucocratic granitoids (leucocratic tonalite, leucocratic granodiorite, and leucocratic quartz monzodiorite), mesocratic granitoids (tonalite, granodiorite, and quartz diorites), and abundant aplitic and pegmatitic dikes. The sequence of intrusion is as follows gabbro-diorites→mesocratic granitoids→granites and aplites and pegmatites associated with granites →leucocratic granitoids, based on emplacement relationships. Geochemically, this complex is metaluminous (ACNK=0.87) to peraluminous (ACNK=1.15). The mineralogical, lithological, and geochemical studies along with field observations indicate that the Alvand granites have S-type characteristics, leucocratic granitoids are arc-related I-type intrusions, mesocratic granitoids (tonalite and quartz diorites) possess transitional H-type features and granodiorites have S-type attributes. This complex has petrochemical characteristics that span the high K calc-alkaline and calc-alkaline series and displays the geochemical characteristics typical of magmatic arc intrusions related to an active continental margin. Depletion in Ti, Nb, Ta, Zr, Hf, Y, and HREE and enrichment in K, Rb, Cs, Th, and LREE are consistent with an arc setting associated with the subduction of Neo-Tethyan oceanic crust beneath the Sanandaj-Sirjan zone.