The peridotites from Marivan-Kamyaran ophiolite suite (MKO), outer Zagros ophiolite belt, western Iran, are studied for the petrological and geochemical characteristics. Both mantle and crustal peridotites are present in the Marivan-Kamyaran ophiolitic sequence. Extensive compositional variations in MgO, Al2O3, Cr, Ni and Al2O3 / SiO2, combined with the abyssal (MOR) and supra-subduction zone (SSZ) nature of the peridotites, are indicative of variant degrees of depletion of the mantle peridotites. Various degrees of depletion are consistent with a wide range of partial melting percentages (10-15%) obtained from non-modal backward partial melting models. The enrichment in HFSE such as Hf, Ti, Ta and Th indicates melt-rock interaction in the mantle peridotites; while, the enrichment in U and LIL elements such as Cs, Rb, Pb is most probably related to the fluid-rock interaction. It is suggested here that MOR nature of a part of the mantle peridotites in the region has been changed to SSZ characteristics in later stages through processes such as melt-rock interaction. It is likely that, similar to other occurrences of outer Zagros ophiolite belt, mantle peridotites from MKO with MOR and SSZ characteristics had been originated in MOR setting, before their composition were modified in a SSZ environment.

Introduction The Heydarabad ophiolitic melange is hosted by the Nehbandan Ophiolite Complex (NOC), which crops out in the Sistan Suture Zone (SSZ) that marks the boundary between the Lut and Afghan continental blocks. The major rocks of this area include mantle peridotites, listwaenite, gabbronorite, cumulate and layered gabbro, pillow basalt and deep-sea pelagic sediments that were formed in the mid-ocean ridge (MOR). Olivine, orthopyroxene, clinopyroxene and spinel are rock forming minerals of Heydarabad ophiolite mantle peridotite. Materials and methods After field studies, thin and polished sections were prepared for petrological and mineralogical studies. Whole-Rock major and some trace elements were obtained by X-ray fluorescence (XRF) spectrometer for SiO2, TiO2, K2O, Al2O3, FeO, CaO, Na2O, Cr2O3, MnO, MgO and NiO. Trace element and rare earth element (REE) concentrations were determined by using a Thermo Series X-I inductively Coupled Plasma Mass Spectrometer (ICP-MS). Also, 8 thin-polished samples (least fractured and altered) of wall rock were analyzed by electron probe microanalysis (EPMA), using a Cameca SX100 at the Iranian Mines and Mineral Industries Development and Renovation Organization (IMIDRO) with a 1-3 μm spot size, 20 nA beam current and a 15 kV acceleration voltage. Result and Discussion Most of the olivines from mantle peridotites are serpentinized. The detailed electron microprobe study revealed very high Mg# (62. 4 to 67 wt. %), Cr# (18. 1 to 34. 5 wt. %) and very low TiO2 content (averaging 0. 05 wt. %) for chromian spinels in mantle peridotites. The Fe+3 is very low (averaging 0. 02 wt. %) in the chromian spinel of mantle peridotites which reflects crystallization under the low oxygen fugacity. The composition of olivine shows that forsterite type (Fo90. 07-90. 90), orthopyroxene is enstatite, clinopyroxene is diopside and spinels are Al-rich Cr-spinel. Tectonic environment discrimination diagrams for the harzburgite and lherzolite shows abyssal environment. Conclusion Hyderabad ophiolite melange consists of peridotite rock units (serpentine and listonite), lherzolite, gabbro, gabbronorite, plate dykes, and pillow lava, which are faulted. The mantle peridotite of this area is composed mostly of harzburgite and lherzolite. Based on mineral chemistry studies, harzburgite and lherzolite have olivine which is forsterite, orthopyroxene which is enstatite and clinopyroxene that is diopside. The peridotites of the study area contain Mg-rich olivines, Cr-spinels and Al-orthopyroxenes and are in the range of deep peridotites based on spinel and olivine chemistry. Also, high Mg value in mentioned minerals and high percentage of forsterite in olivines indicate the tectonic origin of these rocks. Orthopyroxenes and clinopyroxenes are Cr-rich, indicating limited partial melting of peridotites. Mineralogy studies show the relationship of these rocks with the oceanic environment. The composition of spinels in the peridotites shows that the type of high Al, with Mg and Cr is 62. 4 to 67 wt% and 18. 1 to 34. 5 wt%, respectively. They are considered as spinels formed in Abyssal peridotites. Geochemical studies show that Hyderabad peridotites are mantle peridotites that are formed by melting 11 to 16% of a prepared mantle of lherzolitic spinel. The composition of chromium spinels in these peridotites is in the Alpine type range and their tectonic environment is more compatible with MOR peridotites.

The study area is located in northwest of Birjand, northern part of the Sistan suture zone in eastern Iran. There is well preserved outcrops of an ophiolite melange in this area. This complex is composed of harzburgite, layered gabbro and spilitic basalt with flysch type rocks.Microprobe analyses of olivine, clinopyroxene, orthopyroxene and spinel in harzburgites show that olivine is forsterite (Fo90.15-Fo90.75), clinopyroxene is diopsidic augite (Mg#=95.8), orthopyroxene is enstatite (Mg#=91.58), and spinel (Cr#=41) is Al-Cr bearing type. Based on thermobarometry of clinopyroxene and orthopyroxene minerals, crystallization temperature of peridotites is 1016±100 oC at 25 Kbar pressure.

The Dehsheikh peridotite massif, as a part of the Esfandagheh ophiolitic mé langes, is located in the south of Baft, Kerman province. Structural analysis of the ophiolitic complexes play an important role in understanding geodynamics of the orogenic belts. In this research, structural elements of the eastern part of the Dehsheikh peridotite massif as well as prevailing deformational patterns of the area and its relation to the Zagros orogenic belt was studied. The chromitite folds, dunitic/pyroxenitic dykes and ductile to brittle shear zones (faults and magnesite veins) constitute the principal structures of this area. Structural evidence indicate two successive tentional/transtentional and dextral transpressional deformational phases. The early D1 deformation took place in a back-arc basin during ascending of the Dehsheikh Peridotite massif. This caused emplacement of the lithospheric mantle in the low crust level, and was accompanied by deformation of the chromitites and intrusion of the dunitic/pyroxenitic dykes. The next D2 right-lateral transpressional deformation with development of the brittle-ductile shear zones accommodated emplacement of this massif in the high pressure-low tempretaure Sanandaj-Sirjan metamorphic zone.

The Kuhshah ultramafic complex is located in the south-east of Sanandaj-Sirjan metamorphic zone, near the probable remnants of Neotethys plate in Iran. It consists of highly depleted harzburgites, dunites, chromitite bands and altered gabbros. The ultramafic parts have been intruded by numerous clinopyroxenite dykes and veins. In the harzburgites, there are different generations of olivine, orthopyroxene and spinel. The chemical composition of the first generation minerals indicates that the harzburgites are depleted in incompatible elements, but the other generations show melt/rock interaction features which can be found in a suprasubduction zone setting. During subduction of the Neotethys plate beneath the Sanandaj-Sirjan zone, a back arc basin developed between the Sanandaj-Sirjan arc and the central Iranian microcontinent. Whole rock and mineral chemistry, specially, cromespinels, show that the harzburgites formed underneath this basin. After depletion, ascending melts with boninitic compositions reacted with these peridotites to form dunites and chromitite bands. The updoming and decompression of the mantle in the next stage, led to remelting at deeper levels and development of clinopyroxenite parental melts which intruded into the uppermost mantle. Then, the new basin closed and the Kuhshah peridotites were emplaced in present position.

Part of the Ultramafic Sorkh-Band complex along the Kahnuj, Roudan, Minab Ophiolite belts Hormozgan Province at Nazdasht area, contain harzburgaite, dunite, and serpentinit (with dominance harzburgaite). The major mineral in these rocks included olivine, orthopyroxenes and minor mineral such as Spinel. Mesh and granoblastic texture is dominance in these rocks and tectonic pressure effect can be seen as kink band and undulose extinction within the minerals. Results from Electron Microprobe analysis of minerals show olivine with (Fa 90. 18-93. 6) forsterite composition and rich of magnesium that belong to Alpine type. Also orthopyroxenes show (En 32. 8-95. 2) enstatite composition and spinel Cr# (53. 9-71. 02) have chrome. The harzburgites have high Mg# (97. 78-84. 65) but are poor of Al2O3 (0. 71-0. 34) and Ca (0. 69-0. 45), which can be said these rocks are refractory waste that have been remain after the partial melting of more than 25% percent. Low amount of Al and Ti (0. 01-0. 04) in spinel existence at the Nazdasht harzburgites consider to be characteristic of supra-subduction zone peridotites.

By intrusion of gabbros in mantle peridotites of the Central Iran ophiolites, a chemical potential gradient established and new metasomatic rocks are formed in contact zone. These rocks produced by this special type of contact metamorphism, are clinopyroxenite, olivine clinopyroxenite wehrlite, lherzolite plagioclase peridotite and troctolite, from mantle peridotite side to the gabbro side. The studied rocks are formed at the expense of peridotitic part of the contact zone. The occurrence of these types of reactions in ophiolitic associations are required a careful sampling and attention should be focused on the interpretation of gabbroic, peridotitic and pyroxenitic rocks data.

Shesat Pich region hosts an ophiolitic complex located in the south of Kerman, southeast of Iran. This ophiolitic complex is composed of lherzolite, harzburgite and dunite. Olivine is one of the important minerals found in these rocks, which is observed along with pyroxene (orthopyroxene and clinopyroxene) and spinel in the rocks of the region. The combined range of olivines in the region is in the forsterite range of 84 to 92% and ranges from forsterite to chrysolite. NiO with an average amount of about 0.38% by weight and MnO with an average of 0.14% by weight in olivines show the range related to abyssal peridotites. In addition to serpentinization as a general change in the ultramifics of the region, petrographic studies show evidence of metamorphism in the olivines of some harzburgites along with recrystallized antigorite crystals, which indicate a phase of thermal metamorphism in this harzburgite. These results have been confirmed in mineral chemistry studies too. Metamorphic olivines have an abnormality compared to magmatic olivines with a decrease in calcium. In chemical mineralogical studies, the amounts of forsterite and olivines show a regular increase from lherzolite to harzburgite and dunite. Raman spectroscopy studies on the studied olivines show the relationship between the peak shift of 854 waves/cm and forsterite values of olivine minerals in the region.

The Loghar ophiolite is located in ophiolitic belt of Kabul block (southeast of Afghanistan) and it is a part of Neotethyan ophiolites in Alpine - Himalayan orogenic system with Eocene age. Olivine, orthopyroxene, clinopyroxene and spinel are rock forming minerals of Loghar ophiolite mantle peridotite. Most of the olivines from different rock types are serpentinized but some fresh are present with forsterite composition. Orthopyroxene and clinopyroxene are enstatite (Mg# 0.961-0.972) and diopside (Mg# 0.976-0.999) in composition. The Cr# of vermicular and unhedral spinels of lherzolite and subhedral reddish brown spinels of harzburgite are 0.547 and 0.625 respectively. The Cr# of subhedral to euhedral spinels of dunite is 0.477, induced by high content of Al2O3 and low level of Cr2O3. The Cr# of dark red and euhedral spinel of chromitite is 0.633. The peridotites of the studied area belong to sub-oceanic crust mantle. The low content of Al2O3 in pyroxenes (opx and cpx) and the low amount of Na2O in clinopyroxene indicate high degree of partial melting of mantle peridotites. The chemical compositions of minerals in dunites are different from that of lherzolite and harzburgite but present considerable similarity with that of the pillow lavas. The dunites of Loghar mantle peridotite (LMP) do not share features with those derived by partial meltiny, but represent sub lithospheric melt channels.

The Lerdgarm peridotite complex is one of the ultramafic complexes in south-east Iran. This complex is composed mainly of harzburgite dunite, lherzolite, and secondary listvenite and magnesite. The detailed electron microprobe study revealed very high Cr # (39.9-64.0), Mg # (51.2-65.63) and very low Ti02 content (averaging 0.05 wt %) for chromian spinels in peridotites. The Fe3+# is very low (<0.05 wt'l/o) in the chromian spinel of peridotites which reflects crystallization under the low oxygen fugacity. The composition of olivineshows forsterite type (Fo90.97-92.63), orthopyroxene is enstatite, clinopyroxene is diopside and spinels areAl rich Cr-spinel. Thermo-barometric study of Cpx-Opx suggested that the re-equilibrium temperature of peridotites was 1100oC± 60 at a pressure of 26 Kbar. Tectonic environment discrimination diagrams for dunites show a suprasubduction environment of the arc setting and for the harzburgite and lherzolites show abyssal environment.