Petrology and Geochemistry of Qareaghaj Mafic - Ultramafic Intrusion, NW of Urmia

Qareaghaj mafic-ultramafic intrusion (QMUI) is located in northwest Iran, 36 km NW from Urmia city. The QUMI is composed mainly of non-mineralized mafic and Fe-Ti-P-rich ultramafic rocks (FTP). The mafic rocks, mainly coarse-grained gabbro, microgabbro, metagabbro and ortho-amphibolite, have simple mineral assemblage (plg + cpx + ilm). Based on field observations, petrography and geochemistry, they are directly related to each other (comagmatic). The FTP forms numerous layers and sill-like bodies, ranging in thickness from ~5cm to several meters. These rocks with high proportions of olivine, apatite, ilmenite and magnetite, show unusual bulk composition (e.g., SiO2~21-30 wt%, Fe2O3t ~ 26-42 wt%, TiO2~5-11 wt%, MgO~9-20 wt%, P2O5 up to 5.1 wt%, Cr~40-160 ppm, Ni~7-73ppm, ∑REE~10-340ppm). The FTP totally included by mafic rocks with sharp and concordant contact shows magmatic lamination and follows general NW-SE trend of the QMUI. Field relationship, petrography and geochemical data suggest that the FTP is not related to mafic host rocks and indeed intruded later into gabbros during plastic, high temperature deformation in local shear zone.