Petrogenesis and geodynamics of clinopyroxenites in faryab metaultramafic sequence (south of Kerman province); Evidences for mantle heterogeneity in southern Iran

The Faryab ultramafic complex with Paleozoic age, located in the south east of Kerman province, Iran. Field evidences show that it has emplaced in the Bajgan metamorphic complex after metamorphosing the Bajgan units, and includes harzburgite, lherzolite, dunite, clinopyroxenite, and chromitite. Clinopyroxenite has intruded into the peridotites in the form of dykes and veins and their cumulate texture, indicate that these rocks have crystallized from silicate melts. Mineral chemistry reveals a mantle origin for them (Mg# of Cpx = 91–94) and their whole rock composition is not similar to MORBs and mantle-depleted peridotites (Ni up to 720 ppm and MgO = 32.4 wt%); however, they are depleted in LILE and LREE compared to HREE similar to well-known clinopyroxen asite cumulates. The whole rock chemical composition of Faryab clinopyroxenits (SiO2 = 50.67 and Cr = 6180 ppm) suggests that the parent magmas were probably Low-Ca boninitic melts. These boninites derived from the reaction between primary calcium rich picritic melts and the host peridotites and as they ascend through fractured lithospheric peridotites, leaving behind the Faryab clinopyroxenites. The parallel alternating of clinopyroxenites suggest that the upper mantle in this region likely rose diapirically, causing pressure reduction and partial melting of the upper mantle and resulted in the formation of parallel fractures in the lithosphere. The Faryab clinopyroxenites can be considered as channels through which the supra-subduction zone melts of the Neotethys lithosphere ascended and formed them as relatively high pressure cumulates. The presence of clinopyroxenites and their petrogenetic evolution provide undeniable evidence of upper mantle heterogeneity in south of Iran.