Geochemistry of chromite deposits in the Sistan suture zone as an indicator for tectonic setting in East of Iran

چکیده مقاله

Sistan suture zone, eastern Iran, which marks the closure of an enigmatic branch of the Neotethys Ocean associated with the collision between the Lut and Afghan continental blocks and represents the the Early to Middle Cretaceous oceanic lithosphere of the Sistan ocean. Several chromite pods have occurred in this zone which display nodular, massive, disseminated, banded and brecciated textures and have serpentinized dunitic envelopes that grade into the surrounding harzburgite and clinopyroxene-bearing harzburgites. Chromian spinels compositions in chromitites, harzburgites and dunites in these areas form a continuum from Cr# = 0.460 to 0.680, and a wide range of Fe3+/ΣFe ratios from 0.022 to 0.680. These chromitites show that they have Cr2O3 contents from 36 to 52 wt. %, and a range of Al2O3 contents (16–31wt. %) and are Al rich as similar as those of MOR magmas but with higher Cr2O3 and lower Al2O3 from east to west in Sistan suture zone.