جستجوی مقالات مرتبط با کلیدواژه « افیولیت » در نشریات گروه « زمین شناسی »

The mantle sequence of the Kuh-Siah ophiolitic suite is located in N Sabzevar, Central Iran structural zone and consists mainly of harzburgite, dunite, lherzolite, pyroxenite, and chromitite lenses.  The Fo% of olivines in peridotites ranges between 91-96%, and plotting them in the Ezubonin-Mariana peridotites. The Al2O3 content of orthopyroxene in harzburgites and lherzolites is relatively low, showing a tendency towards orthopyroxenes of forearc-abyssal peridotites. The clinopyroxene in the pyroxenites also has low Al2O3 and TiO2 content and placing it in the forearc peridotite field. While this mineral in harzburgite and lherzolites have a higher content of Al2O3 and TiO2 and plots in the abyssal peridotites field. The spinel in lherzolites resemble oceanic peridotites, while in harzburgites, it shows a tendency towards forearc and oceanic peridotites. The spinels in dunites exhibit high Cr# and appear to be derived from a boninitic melt in high degrees of partial melting from a depleted mantle source under hydrous conditions. Based on minerals chemistry characteristics (indicating the dual nature of the MORB_IAT_BONINITIC), the evolution of this mantle sequence has been involved in a supra-subduction zone, resulting from the northward subduction of the sub-branch of Neotethys Ocean (Sabzevar suture) beneath the Alborz during the Cretaceous.

The south of Bavanat area is located in the high Zagros zone and it is considered a part of the Neyriz ophiolite. In this area, the ophiolitic complex is small coloured melanges include radiolarite cherts and serpentinites. The serpentinites composed of serpentine, spinel, opaque (as residual minerals from protholith), amphibole, rarely olivine and pyroxene. Olivines have been highly altered to serpentine and pyroxenes to bastite. Low values of Al2O3 and very low TiO2 against high values MgO, Cr, Ni and V in these serpentinites indicate the protholith of harzburgite- dunite tectonites. Also, very low values of CaO in these serpentinites indicate the low amount of clinopyroxene in the protholith and its harzburgite-dunite type. Based on the chemistry of the major, minor and rare elements, the primary peridotites that make up these rocks are formed in the suprasubduction-fore arc zone from a mantle affected by the reaction with the melt (melt-rock reaction) resulting from the subducted plate.

The studied area is located in the high Zagros zone and it is considered a part of the Neyriz ophiolite. In this area, the ophiolitic complex is small coloured melanges include radiolarite cherts and serpentinized ultrabasic rocks. The main lithological unit is serpentinized ultrabasic rocks, which have a variety of colors from dark to light brown and dark to light green. These ultrabasic rocks have composed of olivine, pyroxene, amphibole, opaque, serpentine and spinel. Olivines have been highly altered to serpentine and pyroxenes to bastite. Based on whole rock chemistry, the studied rocks are basic and ultrabasic cumulates type (lherzolite-harzburgite) with a composition close to the average composition of the mid-ocean ridge basalt (MAR). Based on mineral chemistry, pyroxenes are calcic type and in the range of diopside and augite, and amphiboles are calcic and actinolite type. Pyroxenes have crystallized under conditions of low oxygen fugacity, temperature higher than 910 °C (1100 - 1200 °C) and pressure more than 2 kbar (2 to 10 kbar). Amphiboles have crystallized at a temperature below 700 °C and a pressure less than 1 kbar. Based on the geochemical characteristics and mineral chemistry, the ultrabasic rocks in the Koopan area were formed in a subduction zone.

The subduction and closure of the vast Neo-Tethys ocean between the Arabian and Eurasian plates has left numerous ophiolitic traces, the unique position of Iran in its central part is noticeable. The lack of information, right on the border of Iran with Iraq and Turkey, due to security considerations, has so far prevented the overview of this suture zone in the northwestern border of Iran. Adding Gysian ophiolite in southern Urmia as a missing link in this stretch can partially cover this lack of information. A comparative study of whole rock chemistry of serpentinites in the central part of the Neo-Tethys ophiolites, considering several sectors from Iran (Kamyaran, Marivan and Gysian), Iraq (Penjwin and Mawat) and Turkey (Guleman and Osmanie) in this article, indicates that they belong to subducted serpentinites, whether they were originally formed in the fore-arc environment or the at abyssal oceanic environment. Composition of the serpentinites of the central part of the suture zone is similar to the average global serpentinites which have mostly lizardite/chrysotile. All of them show depletion of Mg resulting sea floor alteration during serpentinization. The mentioned point may be caused to data deviation from abyssal peridotites field. Considering that the transition metals contents the confirmed the above setting. Almost all of the studied serpentinites are from subducted type which indicates refertilization of LILE evidences as a result of rock/fluid interaction through serpentinization.

The Mazraeh manganese deposit (southwest of Maku, north of West-Azarbaidjan Province, NW Iran) is developed in the form of scattered lenses at the contact of pillow basalts and pelagic limestones, belonging to the Khoy-Maku ophiolitic complex. Mineralogically, the ores mainly contain pyrolusite, psilomelane, manganite, and braunite which are accompanied by lesser amounts of hematite, goethite, quartz and calcite. The distribution pattern of REE normalized to chondrite along with some geochemical parameters related to lanthanides, such as La/Ce, (La/Nd)n and (Dy/Nd)n, show a hydrothermal origin for this deposit. This idea is supported by some geochemical diagrams (Co/Zn vs. Co+Ni+Cu, Zn-Ni-Co, and Mn-Fe-[(Co+Ni+Cu)]×10) and elemental ratios such as Mn/Fe, SiO2/Al2O3, U/Th, and Co/Zn. The high concentration of lanthanides in ores (on average of 767 ppm), compared to known hydrothermal manganese deposits, reveals the effects of diagenetic processes on this deposit. The occurrence of negative anomalies of Eu and Ce indicates the low-temperature hydrothermal fluids, responsible for the mineralization. The presence of detrital materials in the ores can be inferred by the concentration values of oxides like Al2O3 and TiO2.

Gysian ophiolite is a remnant of the Neotethys, located in the north-west Iran at the intersection of the ophiolite belts of south-eastern Turkey, north-eastern Iraq and north-western Iran. The geochemical comparison of the soils with the average of global rocks and the study area led to determination of the composition group of the region soils. The geochemical evidence of the first group of soil samples with low silica percentage by Harker and triangular diagrams is close to the position of ultramafic rocks of the region (serpentenites) and primary mantle and expresses their compositional similarity. The second group of soils ranges in the area between the earth's crust and basalt, and they show more distribution near basalt. The normalized pattern of REE rare earth elements in this group of soils is similar to the mafic rocks pattern in the region, also in the minor elements chart, they classified in the mafic group. Soils with high percentage of silica in the diagram of major and minor element oxides are located near the positiion of meta-plates rocks in the region, in the range between the earth's crust and global shale. So, this suggests the intermediate composition of their origin. Most likely, the tectonic setting of the three soil groups is based on the oxides of the main elements of the active continental margin.

The studied area is located in the high Zagros zone and it is considered a part of the Neyriz ophiolite. In this area, the ophiolitic complex is a small coloured melange including radiolarite cherts and serpentinized peridotite rocks. The peridotite rocks are mostly serpentinized harzburgite. The peridotite rocks are mostly serpentinized harzburgite. These rocks composed mainly of olivine, pyroxene, serpentine and spinel, where olivines have been strongly altered to serpentine and pyroxenes to bastite. So, serpentine group minerals are seen in abundance in these rocks. Also, spinel is found in amorphous and amoebic shape in these rocks. Based on mineral chemistry, serpentines are in the range of stability of all three mineral phases, i.e. lizardite, chrysotile and antigorite, and the range of pseudomorphic serpentinites, which shows they are the result of the regressive replacement of olivine and pyroxene with serpentines. Also, these minerals are mostly located in Ol-mesh and Cpx bastite ranges, which shows they are the result of regressive metamorphism of harzburgite and dunite rocks. The spinels are Cr- spinel and pleonaste type. These Cr spinels are ophiolitic type and have residual nature. The low TiO2 and the enrichment of these spinels from Cr is similar to spinel in fore-arc harzburgites. Also, these spinels, in addition to having the characteristics of alpine peridotites, are placed in the overlapping range between suprasubduction (SSZ) and abyssal peridotites. So, the studied serpentinized peridotites are formed from high degrees of partial melting (25-30%) of a depleted mantle in a suprasubduction (SSZ) - fore-arc setting.

The nickel-bearing laterites of Noorabad area are seen in the high Zagros zone along with Kermanshah ophiolitic complex. The ophiolitic complex in the studied area includes serpentinized peridotites, isotropic gabbros, plagiogranite, sheeted dykes, basaltic lavas, andesite, and radiolarite. The peridotites of this ophiolitic complex include dunite, harzburgite, and lherzolite. The tectonic activities have caused tectonization in these rocks in such a way that it has facilitated their alteration process and created laterite zones. The alterations of peridotite rocks include serpentine, dolomite, hematite, and silicification. The laterite zone is layered and lens-shaped red horizon on peridotite rocks and is covered by Miocene limestones. Based on XRD analysis, mineralogy of the lateritic zone includes dolomite, quartz, smectite, and serpentine. The ratio of La/Y changes indicates that the studied laterites were formed in alkaline pH. According to the discrimination diagrams of the source rock, the studied laterites are karst bauxites with ultrabasic origin.

Ophiolite is a remnant part of oceanic crust and consist of the upper mantle and lower crust rock units. The transition from mantel to crust coincides with Moho discontinuity. Ophiolite rocks host valuable minerals for this discrimination of different parts of this unit is important. In the Khoy region for discrimination of different parts of ophiolite, rock units used various band ratio and principal component analyses. Structural analysis in both of micro-and-macro scales was applied to document change in deformation style in the Moho transition zone.The results of this research indicated that remote sensing techniques such as band ratio and principal component analysis are effective tools for discriminating mantle harzburgite and dunite rock units from crust gabbro and basalt. The transition from mantel to crust is accompanied by structural style change. The mantle-related rock unit ductile shear zone with NW-SE trending were dominated structure and caused the propagation of amphibolite and mylonite rock unit. In this unit pyroxene minerals elongated and folded. With the transition to the crust brittle structure such as fault zone with NE-SE trending were dominated. The evidence in the study region Moho discontinuity is exposed in the two different distinct areas and may be related to different ophiolite generations.

Some researchers supposed that investigating the formation of serpentineites can have important applications for understanding the large-scale geodynamics of that earth (Hattori and Guillot, 2003; Hilairet et al, 2007). Serpentineization occurs in a wide range of temperatures and pressures, low temperature serpentinite of alpine type ultramafic rocks occurs due to the penetration of atmospheric waters or from the infiltration of saline waters derived from sediments. This often refers to retrograde serpentineization. In contrast, progressive serpentineization occurs in many metamorphic processes during burial and warming of ultramafic rocks, which includes minimum water, during this process from the reaction of chrysotyl, antigorite and brucite, or antigorite reaction with brucite, forsterite + water were formed (Klein et al, 2014; Evans et al, 2013). The formation of anteatgorite may also occur from the reaction of chrysotyl/lyzardite with talc (Murzin et al, 2013; Lacinska et al, 2016).
After sampling and evaluation of microscopic sections, samples performed by X-ray micro-analyzer by Cansaran Binalood Company. With the aim of studying the whole rock geochemistry, 11 representative samples sent to the Zarazma Company of Tehran and ICP-MS analysis made for rare earth elements and transitional elements and XRF to obtain the major oxide elements.
The remaining olivines were ferro-hortonolite, spinels were chromite, clinopyroxenes were hedenbergite and orthopyroxenes left by serpentineization were ferrosilite. The geochemistry of these rocks is similar to the mantle wedge serpentinites studied along the Neo-Tethys. For example, with Voltri Massive serpentineites in the Italian Alps (Cannao, 2016) or with average subducted serpentinites (Deschamps et al, 2013). The serpentineization of these rocks start from the ocean floor, where the penetration of water in the fractures of the young oceanic crust and in hydrothermal veins, and spread with flat subduction in low temperature metamorphic facies. Since the main serpentine phase in them identified by XRD was chrysotyl, which is associated with the main mineral magnetite, so it is clear that their depth of subduction was low.
The various microstructures identified in these rocks are mesh, sieve, augen, strip, hourly glass, etc. and the effects of elastic (microfolds and kinks) and brittle alteration. The growth of lyzardite plates in the margins of low crystallized mass nuclei is irregular and the increase of serpentine veins and strong deformation reduces the resistance of serpentinites to shear and stress. With precision on the contents, ratios and diagrams, Gysian serpentineites evaluated as subducted type. The content of FME in these rocks is very high and is a sign of re-fertility resulting from the interaction of rock/fluid during subduction stages, which distinguishes it well from other types. In the absence of antigorites in these rocks, the depth at which Gysian serpentineites created was less than 50km. According to the above, Gysian serpentineites are subducted type in the northwestern part of Iran. Along the main Neo-Tethys sutur in Iran, other subduction serpentinites have been reported in Iraq and northwestern Anatolia in Turkey and Gysian serpentinites could be assumed a part of it.

The Dumak ophiolitic mélange in the Baluchistan region is one of the ophiolitic mélanges that contains all of the components of a complete ophiolite, located in the middle parts of the western margin of the Eastern Iranian range. Field studies indicate the presence of a large volume of pillow lavas in different parts of the Dumak mélange. The outcrop of sheeted dikes associated with the Dumak mélange is limited to the Shuru region. These dikes present below the pillow lava and Cretaceous pelagic sediments. Compositionaly, most of pillow lavas and sheeted dikes are basalt. Variations in SiO2 to FeOt/MgO in the pillow lavas and sheeted dikes indicates a tholeiitic trend for their productive magma. The pattern of REE elements and amounts of (La/Sm)N in these rocks are similar to E-MORB. The study of pillow lavas and sheeted dykes of Dumak ophiolitic mélange shows that the MORB ophiolitic body in Dumak has been gradually and continuously evolved in a supra-subduction zone environment and beginning of intra-oceanic subduction. Considering structural evidence of the region, after adding the Dumak ophiolite to the Lut block, during the continuation of tectonic movements related to orocline bending, a new mélange has formed with the presence of Eocene carbonate blocks.

Cheshmeh-Bid chromite deposit is located in Nayriz ophiolite, about 200 km northeast of Shiraz. The ophiolite sequences in this area include ultramafic rocks (dunite, harzburgite, and pyroxenite). In this deposit, chromites are present in the mantle-crust transition zone and are enclosed by dunite. Based on chemical studies of major elements, chromite is depleted from Al and Ti elements and enriched by Fe, Cr and Mg. The calculated values of TiO2, Al2O3 and FeO/MgO indicates that the parent magma is the Boninite magma type with composition equilibrium to the podiform chromites. These chromitites are the result of relatively high melting of the mantle and Boninite melt, which are formed as a result of rising and mixing of magma with mantle harzburgites in the upper environment of the subduction zone. Variations in the chromite mineral composition along with the textural changes in host ores indicate the injection of at least two mineralizing melts in the study area.

Mesozoic-Paleogene ophiolitic sequences in Iran are in association with opening and closing of Neo-Tethyan oceanic crust. Temporally and specially, these ophiolitic sequences subdivided into five different groups (or belts) (Shafaii Moghadam and Stern, 2014):Zagros outer belt (late Cretaceous-Paleogene); Zagros inner belt (late Cretaceous); Sabzevar- Torbat e Heydarieh belt (late Cretaceous-early Paleocene); Birjand-Nehbandan belt (early to late Cretaceous);
Makran belt (late Jurassic-Cretaceous). The Zagros outer belt’s ophiolitic sequences cropped out along the NW-SE trending Zagros main thrust and including Maku-Khoy-Salmas, Kermanshah (-Kurdistan), Neyriz and Esfandagheh (or Haji-Abad) ophiolites. The Kermanshah ophiolite (KO) is an ophiolitic tectonic complex, which comprises imbricated dismembered fragments of mantle peridotites, gabbros, sheet dykes and basaltic rocks which generally occur as thrust-bound tectonic slices. The Sahneh-Harsin ophiolitic complex(SHOC) is the southeastern part of KO. Detail petrological study has not been carried out on the basaltic rocks from Ali-Abad Garos area(AGA) as a part of the SHOC. Thus, the present study focuses on the field observations, petrographic study as well as whole-rock geochemical analyses (XRF and ICP-MS) of the basaltic rocks widespread in AGA.

Regional geology:

KO cropped out in the northwest of Zagros main thrust (ZMT) where Zagros sedimentary belt join the Sanandaj-Sirjan magmatic-metamorphic belt. In SHOC as the southeastern part of Kermanshah ophiolites Triassic-Cretaceous limestone and radiolarites as well as Mesozoic metamorphic-sedimentary rocks are the oldest lithological units. In the following, ophiolitic sequence related lithological bodies such as peridotites, meta-peridotites, gabbros, meta-gabbros, diabasic dikes and volcanic rocks including pillow lava-massive basalts cropped out which are in accompanied by Eocene extrusive and intrusive rocks. Pliocene to Quaternary sedimentary rocks are the youngest lithological units in Sahneh-Harsin region. In Sahneh-Harsin region ophiolitic sequence related basaltic rocks cropped out in Ali-Abad Garos, Tamark, Gashor areas.

We collected ~70 samples of both pillow lava and massive basaltic rocks in-AGA. Based on petrographic characteristics 10 of the freshest samples were analyzed for whole-rock major and trace elements by X-ray Fluorescence (XRF) and Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) in ALS Chemex lab.

Field observations:

Ali-Abad Garos ophiolitic sequence related basaltic rocks mostly show pillow lava structure. However, minor massive basaltic rocks are exist. In the northern part of the study area basaltic rocks are set atop of gabbroic units. However, gabbro-basalt boundary covered by Quaternary sediments. In some parts, basaltic bodies are in association with plagiogranites. Via a fault boundary upper Triassic-Cretaceous limestone units (Biston Formation) thrusted over basaltic rocks.

Petrography:

The rocks under study are dominated by plagioclase (up to 20%), clinopyroxene (up to 10%) and opaque minerals (up to 2%) phenocrysts set in a fine-grained to glassy ground mass. Chlorite, calcite, epidote, quartz, zeolite and opaque minerals as secondary minerals formed by altered phenocrysts and groundmass. Massive basaltic rocks mostly show porphyritic texture and to lesser extent glomeroporphyritic, intergranular and amygdaloidal textures are present. The rocks studied are characterized by plagioclase (up to 10%), clinopyroxene (up to 20%) and opaque minerals (up to 5%) phenocrysts set in a fine grain to glassy groundmass. Secondary minerals in massive basaltic rocks are similar to those presented for pillow lava basaltic rocks. Whole-rock geochemistry, tectonic setting and source characteristics The studied basaltic rocks show tholeiitic signature. Major element oxides values against SiO2 values, as fractionation index, indicate fractional crystallization as an effective parameter in generation of these rocks. In chondrite-normalized REEs diagram, the basaltic rocks exhibit slight LREE enrichment relative to HREEs (LaN/YbN values ranging from 2.91 to 3.35 and Eu/Eu* values vary from 0.91 to 1.01). In primitive mantle-normalized multi-elements diagram, the patterns of basaltic rocks are consistent with plume related mid-oceanic ridge basalts (P-MORB), against within plate basalt (WPB or OIB), normal mid-oceanic ridge basalts (N-MORB) and enriched mid-oceanic ridge basalts (E-MORB). This case is in agreement with situation of the study samples in basaltic rocks with different geochemical signatures on discriminative diagrams. Parallel trends of the studying basaltic rocks on spider diagrams indicate that they are co-genetic. Also, different elemental ratios as well as the situation of the rocks under study in different geochemical diagrams reveal that parental magma (or magmas) could be formed by low degree partial melting (<3%) of a spinel peridotite as a source rock. Integration of our new presented geochemical data from the study basaltic rocks with other previously presented geochemical data from other ophiolitic sequence related basaltic outcrops within (SHOC) (Tamark and Gashor basaltic rocks) reveal that in this ophiolitic complex basaltic rocks are heterogeneous. Briefly, three different groups of basaltic rocks with P-MORB, E-MORB and OIB geochemical features exist in (SHOC). Comprehensive understanding of relation of these three different basaltic groups are needed to further elemental-isotopic geochemical data coupled with geochronological data.

This is the first report on the presence of podiform chromititeLenses associated with the Marivan ophiolite. These ore deposits with granular massive fabric are hosted by dunite and harzburgite occurred in south Marivan city. Chemistry of chromian spinel in the chromite Lenses indicated that Cr#  for two ore occurrences is high (0.85) with very low TiO2, but for the other ore occurrence is lower (0.67) with higher TiO2 (0.05). The finding shows that the chromite ore Lenses and consequently their host ophiolite were developed in two different geotectonical settings. Geochemical data indicated that some of the studied ore deposits occurred during the opening of oceanic crust in a Mid Oceanic Ridge setting from a tholeiitic magma while the others were fractionated form a boninitic melt in a Supra Subduction Zone. Formation of these ore Lenses and the host rocks occurred in response to the very fast divergence and then convergence of Neo-Tethys oceanic crust. A wide range of gabbros including coarse-grained gabbro, melagabbro and microgabbro host ilmenite, magnetite and titanite in three regions at the northwest of Kamyaran (Yakhtekhan village), the east of Sarvabad (Mianeh village) and the south of Marivan (Dragashikhan-Vyseh villages). Ilmenite is found in all the three regions, but magnetite and titanite are only found in the east of Sarvabad. Plagioclase (andesine-labradorite) and diopside, the main rock-forming minerals with minor augite, olivine and amphibole are the minerals of the host rocks. The chemical composition of the ilmenites showed that the average concentration of TiO2 increases from Kamyaran (43.19 wt.%) to Sarvabad (46.09 wt.%) and then to Marivan (47.42 wt.%). These minerals occur as interstitial fine to medium grains (up to 1.5 mm) and often in the amoeboid, anhedral and to a lesser extent as subhedral forms. Based on textural and mineral chemistry evidence, mineralization of titanium occurred as the result of magma oxidation. The oxidation of magma resulted in the formation of iron-titanium immiscible liquid droplets, following the plagioclase crystallization.

Podiform chromite deposits are small magmatic chromite bodies formed in the lower section of an ophiolite complex. The Khoy ophiolite covers an extensive area in the northwest of Iran along the Iran-Turkey border.In this research study 1200 magnetometry data and geoelectric studies along 5 profiles were designed for prospecting chromite lenses. Mineralogical and geological studies have shown that pyrite, magnetite and other metallic sulfides are formed during the serpentinization process in the fractures of chromite lenses. The amount of released magnetite in the chromitites is less than the amount released in the harzburgite and dunites. Therefore, the number of magnetic anomalies created are less than those generated by bedrocks (Imamalipour, 2009). These metal sulfides increase the chargeability of positive anomalies in the cross-sections. Resistivity also shows a significant reduction compared to the bedrocks due to the metallic properties of chromite lenses.

In this research study, geological methods were used to interpret geophysical data in the Khoy ophiolite. Geological surveys at a scale of 1:20000 were implemented in an area of about 70 km2. 1200 magnetic points and resistivity and induced polarization along 5 profiles with a geological map and mineralogical studies were used. Magnetometric data at the 5*10m grid and Ip-Rs data with 10 m interval electrode spacing were collected.  For the inversion modeling of Ip-Rs data, Res2d inv software was used and geological and mineralogical data were integrated with magnetometric results.

Exploration of podiform chromite deposits has been a challenge due to their unpredictable occurrence, small size of most orebodies, and intensive tectonic dislocations (Mosier et al., 2012). Moreover, the absence of primary geochemical halos and associated alteration are issues that lead to difficulties in prospecting for podiform chromites. Chromite is an accessory mineral associated with the harzburgite host rock. The results of geophysical studies show that chromite lenses have lower magnetization than gabbro and higher mangnetization than harzburgite (Frasheri et al., 1995). The reason is the mineralogical conditions of chromite lenses and their host rocks. Mineralogical study showed that some chromite lenses have fractures that are filled with silicate secondary minerals (serpentine). Chromite and serpentine are the main minerals, and hematite and magnetite are minor minerals in the chromite orebodies. Although these minerals have been altered and have mostly been converted to serpentine, the earliest composition is likely to be olivine. Dunite and harzburgites are chromite lenses host rock and are mainly serpentinized and contain fine magnetite particles, which can cause positive magnetic anomaly (Imamalipour, 2009, Masoudi and Imamalipour, 2019). These small metallic minerals cause high induced polarization and the embedded rocks show a higher degree of charge. Because of the metallic nature of chromite lenses, the resistivity has a much lower value. Therefore, using resistivity, induced polarization, and magnetic geophysical methods, chromite lenses can be separated from harzburgite host rocks.

In this study, geophysical resistivity and inductive polarization method with magnetometry, which is one of the most important methods for the exploration of subsurface deposits in the Khoy ophiolitic zone, have been used. As a result, it was found that podiform chromite does not show much difference in the magnitude of the magnetic field. Therefore, this method cannot alone be used to explore chromite deposits. However, the IP-Rs method can be used as a practical method for exploration of these reserves. Chromite lenses have low resistivity values of about 400 to 600 ohm-m. The amount of induced polarization is also much lower than its host rock, with values of 3 to 6 mv/v. Therefore, these properties can be used for chromite exploration at a much lower cost than gravimetric and electromagnetic methods. The reason for these values can also be found in the mineralogy of the chromitite lenses. During the serpentinization process of harzburgite and dunite, magnetite minerals, chalcopyrite, and some metallic elements are released. Released magnetite increases the magnetic properties of chromitite. However, this increase is less than the magnetism of the host rock. The released metallic elements such as chalcopyrite with serpentinite also increase the changeability of the host rocks and chromite lenses with low induction polarization and much lower resistivity could be identified.

Anarak ophiolite, belonging to Paleozoic, formed along with the tectonic evolution of the Paleo- Tethys Ocean, consisting of meta- peridotites of mantle and crust, cumulate rocks, massive gabbros, pillow lava, basic and ultrabasic dikes, rodingite and listwanite covered all by schist and marble units. The olistolithic patches of Anarak ophiolite have commonly exposed in Sebarz schist, within the sole of Chah-Gorbeh complex. Olistoliths composed of listwanite, meta- mafic, serpentinite and meta- peridotite olistoliths varying from centimeter to several hundred meters in size. The results of electron microprobe analyses show that the fundamental rock- forming minerals of the listwanitized olistoliths are chromian spinel and pyroxene, secondary minerals including calcite, garnet, tremolite, chlorite, magnetite and opaque minerals. Meta- mafic olistoliths composed of chromian spinel, sphene, epidote, chlorite and opaque minerals. Serpentinized olistoliths consist of chromian spinel, magnetite, tremolite, talc and chlorite. It also shows that the meta- peridotite olistoliths composed of chromian spinel, chrome-bearing magnetite, chlorite, calcite, garnet and antigorite. Based on the geochemical analyses, Cr# in the listwanite patches, meta- mafic, serpentinite and meta- peridotite olistoliths are 87.40- 97.92, 49.38- 51.89, 49.22- 60.05 and 29.76- 55.97 respectively with very low amount of TiO2. The different in chemical composition of minerals in the North Anarak complex shows different petrogenesis for ophiolitic olistoliths suggests characteristic of the MORB and/or supra- subduction zone.

Sahneh, Harsin-Nourabad ophiolits (Kermanshah Provience) located in outer Zagros ophiolitic zone and are parts of the Cretaceous ophiolitic belt, as remnants of southern branch of the Neo-Tethys Ocean obducted over the Arabic–Tauric platform from Oman to northwestern Syria, Cyprus and Antalya. Calculation of Fe/Mg separation coefficient of olivine indicates the mantle origin of this mineral. Textural evidence of ultramafic rocks displays clear evidence of cooling with decompression, partial melting and melt-rock reactions. Tectonomagmatic discrimination diagrams show that peridotite samples are located in olivine- spinel mantle array and SSZ peridotite field. Based on geothermobarometry calibration the temperature and pressure of crystallization of harzburgite and lherzolite rocks were 1100 to 1500 ° C and 12 to 18 Kbar and the wehrlite sample was 1200 to 1500 ° C and 21 to 23 Kbar, which corresponds to the SSZ tectonic environment.

The Abgarm ultramafic complex in south of Kerman Province and also southeast of  Sanandaj – Sirjan zone is a part of Esfandagheh- HajiAbad ophiolitic belt. Most ultramafic rocks are harzburgite, dunite, and lherzolite. Dunites form the largest volume of ultramafic sequence in the study area after harzburgite and they are scattered into the mass form of harzburgites. Due to the present of several faults, it is difficult to detect the initial relationship between the dunites and the harzburgites in the region, and they are sometimes severely serpentinized. Olivine is the most abundant mineral in the dunites of the Abgarm ultramafic complex. The amount of forsterite in these minerals varies from 72.91 to 84.90 and the high amounts of forsterite in the olivines in the dunites, as well as the composition of the chromium spinels in these rocks show that peridotites belong to the mantle and have ophiolitic and depleted nature and probably are formed inn the back-arc basin environment by the reaction of the basaltic melts of the back-arc basin with peridotites. Then they were replaced tectonically as a part of the ophiolite mélange in the crust.

Abgarm ultramafic complex in termination of the southeast of Sanandaj- Sirjan is a part of the Haji Abad- Esfandagheh ophiolitic belt. This body consist of three different types of rocks includes of ultramafic rocks, mafic and metamorphic. Most ultramafic rocks are harzburgite, dunite, and lherzolite that harzburgites are more than 85 volume percent of this complex. Microscopic evidence suggests that there are several generations of minerals in these rocks. In addition, mineral chemistry data indicate that the Abgarm harzburgites have been formed in an environment similar to those considered for MORB peridotites and they passed about 15% partial melting. Pyroxene porphyroblasts and Olivin- Spinel thermometry in these harzburgites shows 816- 992 and 708- to 840 0C. Moreover, fO2 calculation gives a redox state that lies within a range of 1.6 log bar units around the Fayalite–Magnetite- Quartz buffer FMQ (log = -0.8 - 0.9 log-bar units) in the range of pressure of 1.2 and 2 GPa. For them and suggest that they have been equilibrated in spinel peridotite field for Abgarm peridotites. Chemical evidence shows that these rocks are similar to abyssal peridotites and probably formed in a back-arc basin environment.

Kamyaran ophiolitic complex located in the northeast Zagros orogeny along the crush zone between Arabian-Iranian plates. This complex outcropped between the Harsin ophiolites in southeast and Sarwabad ophiolite in northwest. Field observation reveal the fact that the Garmab Ophiolite in the northeast of Kamyaran is a tectonic mélange including peridotites and gabbros cut by microgabbroic dikes. Olivine, clinopyroxene and orthopyroxene with chromian spinel made the peridotites minerals with mesh and porphyroclastic fabrics and Gabbros include plagioclase, clinopyroxene and minor amphibole with intergranular, pegmatoidic and interstitial texture. According to the geochemical results, gabbros have tholeiitic to calk-alkaline nature and show the MORB to island arc characteristics. According to the geochemical and geotectonic results, Garmab peridotites plotted to the abyssal peridotites area that represent from the residual mantle spinel lherzolite after extraction of 15–20% partial melting. The break-off of Neo-Tethyan slab and subduction of this slab branch beneath the oceanic lithosphere during cretaceous led to cessation of the Neo-Tethyan subduction beneath the Sanandaj-Sirjan block, and forming arc-back arc basin (second step of subduction) and related rocks in the Kamyaran ophiolite. Presence of tholeiitic to calc-alkaline magmatism is in response to the slab retreat in the Eurasian continental margin.