PETROLOGY AND GEOCHEMISTRY OF THE GRANITOID COMPLEX OF BOROUJERD, SANANDAJ-SIRJAN ZONE, WESTERN IRAN

Abstract

The Middle Jurassic Boroujerd Granitoid Complex of the Sanandaj-Sirjan Zone (with a U–Pb zircon age of 169–172 Ma) was emplaced in an active continental margin setting. This complex consists of three main units: an elongate NW–SE extending granodioritic unit (SiO2 = 58–71 wt%), which is widespread throughout the area, a quartz-dioritic unit (SiO2 = 52–63 wt%), exposed as small stocks within the granodioritic body, and a monzogranitic unit (SiO2 = 70–75 wt%), widely scattered as separate small outcrops through the southern part of the area. A series of NW trending aplites and pegmatites are present in the granodioritic unit and its aureole.Geochemically this complex is metaluminous to slightly peraluminous, typical of I-type granites. It belongs to high-K calc-alkaline series and displays the geochemical characteristics typical of volcanic arc granites related to an active continental margin (e.g. significant Nb, Ti, P and Sr depletion). Isotopic data (Sri = 0.7062–0.7074 and εNdt = −3.02 to −3.62) are consistent with a crustal protolith. In addition, fractional crystallization may have played an important role in the formation of the whole spectrum of the granitoid types that occur in the Boroujerd area.