Gabbro from the Kalaybar, Hasht-Sar; subduction-related metasomatism effect

In the Kalaybar Hasht-Sar area، in the western part of secondary Palaeo-Tethys suture zone (NW Iran)، gabbro intrusion، which is older than Paleocene in age، has cropped out. This gabbro is shoshonitic in composition with has arc type geochemical composition. The rocks show high K2O concentration and enrichment of Rb، Ba، U، Th and Pb and depletion of Ta، Nb، Ti also Hf، Zr on primitive mantle-normalized spider diagrams. The parental magma of gabbro is formed by low partial melting rate (less than 10%) of spinel-garnet lherzolite. According to trace elemental ratios، the gabbro was derived from a source strongly modied by subducted slab uids. Then crustal contamination caused the LILE enrichment in the magma. Considering accompany of the rocks with Palaeo-Tethys suture zone suit، it seems that gabbro was formed due to subduction of this oceanic crust. Metasomatism above subduction zone is an important process that produced heterogeneous mantle and thus changes in geochemical ratios of the magma.