Using noble metal and mineral chemistry of peridotites in petrogenesis and tectonic setting of Rudan ultramafic complex, Kerman, Southern Iran

The Rudan ultramafic complex with Paleozoic age is located in Southern Kerman province and is composed mainly of massive harzburgite, small to medium sized lenticular dunite and subordinate very thin olivine websterite dykes. Granular and protogranular are the main textures in dunites and harzburgites, and orthopyroxene, olivine and to a lesser extent clinopyroxene and chromian spinel were found in the harzburgites and dunites. The forsterite content of olivine is slightly higher in dunites (Fo92.5) than those in harzburgites (Fo91). Detailed electron microprobe study reveals intermediate Cr# (0.33-0.56), relatively high Mg# (0.59-0.75) and very low TiO2 content (averaging 0.01 wt %) for chromian spinels in Rudan peridotites. The Fe3# is very low, (s in the peridotites are very low (average 25 ppb) and are highly depleted in PGE contents relative to chondrites. The PGE spidergrams in dunites are unfractionated, and the PdN/IrN ratios averages 1.02, whereas the harzburgites show slightly positive slopes PGE spidergrams, together with a small positive Ru, Pd and Au anomalies, and their PdN/IrN ratio averages 2.75. Moreover, the PGE chondrite and primitive mantle normalized patterns of the harzburgites are relatively flat which are comparable to the depleted mantle peridotites indicating relatively high degree of partial melting (about 17-22%) of the mantle source. The mineral chemistry data and the noble metal geochemistry indicates that the harzburgites of the Rudan ultramafic complex are residual and dunites are replaced and tectonically have been generated in a fore-arc mantle region above a supra-subduction zone setting.