نشریه پترولوژی
پیاپی 41 (بهار 1399)

The Noorabad-Harsin ophiolite complex as part of the Kermanshah ophiolite is located in the high Zagros zone. The ophiolitic complex from the lower part to upper part is composed of serpentinized peridotites, layered gabbro, isotropic gabbro, plagiogranite, sheeted dike complex, basaltic lava, andesite and sedimentary rocks, respectively. The structure such as orientation and elongation of crystals in these rocks show that Noorabad-Harsin peridotites have been formed in the upper mantle and then emplaced in the crust. The detailed electron microprobe study olivine composition is forsterite with Fo (91-93). The composition of pyroxenes is diopside and enstatite with low contents of TiO2 and Al2O3. The study of chrome spinels has high Cr # (57-80), Mg # (61-89) and very low TiO2 content which indicate the ophiolitic and depleted mantle origin. The serpentines have Al2O3 content in the range of 0.01 to 10.42 wt. % with SiO2 content between 36.75 to 41.08 wt. percent and are chrysotile and lizardite. Low modal of clinopyroxene, Mg rich olivines and high Cr# content and Cr/Al ratio of chromian spinel from ultramafic cumulates indicate that dunites and harzburgitic rocks have formed by high degrees of partial melting. The chemical compositions of different minerals show different petrogenesis for ultramafic rocks of the Noorabad- Harsin ophiolite complex and show characteristics of the abyssal environment to supra-subduction zone. It seems these peridotites have derived by high degree partial melting of the depleted and sub-oceanic mantle in a supra-subduction zone-Fore arc and have same properties with residual mantle peridotites.

In the Talesh area (western Alborz), a thick sedimentary- volcanic association formed in a littoral- deltaic environment during the Late Cretaceous. The extrusives comprise volcanoclastics (tuffs), lava flows (pillow and massive) and basic dykes. The lava flows are dominated by basalts. Basalts are petrographically diverse including clinopyroxene- and plagioclase- phyric suites. Clinopyroxene is chemically in the ranges of augite to diopside and plagioclase is labradorite to bytownite. Here, using clinopyroxene chemistry, we performed thermobarometry and hygrometry calculations. Thermometric results of different samples are in the ranges of 1000 to 1200 °C. Moreover, barometric calculations show pressure ranges of <2.5 and 2.5 to 6 kbar correlating with crystallization depth of upper to middle continental crust (<10 to 22 km). Regarding parental melt chemistry and the magmatic series, the clinopyroxene and whole rock chemistry suggest two alkaline and subalkaline series. Hygrometric calculations provide H2O contents of 2.7- 2.97 and 2.97- 3.53 wt.% for alkaline and subalkaline basalts, respectively. Tectonically, the alkaline basalts could be related to extensional tectonic regime, asthenosphere upwelling or mantle plume/hot spots, while the subalkaline basalts resulted from subduction- related magmatism probably related to northward subduction of an oceanic basin beneath western Alborz or a Neo-Tethyan branch below southern margin of the  Eurasia.

The Garmichay area in the north of Mianeh, NW Iran, features schists, amphibolites, calc-silicates, marbles and granitoids. Granitoids are of S- and A-type nature. Partial melting is the main generation mechanism, the progenitor is a pelite enriched in muscovite and the major melting reaction is muscovite dehydration. The ASI for the S-type granite varies between 1.12-1.5 indicating peraluminous character and crustal origin. Both granitic types are enriched in LREE in relation to HREE with negative Eu anomalies. Lan/Ybn ranges are 1.49-3.09 and 1.34-1.99 for the S-type and the A-type granites, respectively. Moreover, Lan/Gdn varies between 2.45 and 5 for the S-type granite and 1.53 and 1.75 for the A-type granite. The S-type granite has been generated in a collisional zone during Assyntic Orogeny.The A-type granite, however, is formed in a within-plate environment.The A-type granite belongs to A1 subtype formed in a continental rifting setting. The crystallization temperatures for the S-type and the A-type granites vary from 650 to 750 ºC and 800 to 850 ºC،respectively.

The Lakeh-Siah region is situated in the Central Iran Zone (CIZ), 40 km northeast of Bafq city in the Yazd province. The rocks of the study area belonging to the lower Cambrian; including rhyolite, andesite and pyroclastic surge with porphyry to glomeroporphyric textures. The intrusive igneous rocks occur as stock and dyke and have monzonitic and dioritic composition with intergranular and granular textures. Based on geochemical studies, the rocks under study are calc-alkaline, metaluminous to peraluminous nature. The study apatite shows LREE- enrichment relative to HREE, this is a remarkable feature of the Kiruna- type iron deposits. Also, the enrichment of LILE (such as Rb, Ba, La, U, K and Th) and depletion of HFSE (such as Nb, Ta, Zr and Y) in the host rock, is known as a characteristic of the magmatism in the subduction zones. Based on the concentration of rare and trace elements, the volcanic and to the magmatic arc setting. The overall evidences demonstrate that the primary intrusive rocks belong magma of the rocks have been generated from partial melting of oceanic crust, during the closure of the Proto-Tethys Ocean. Iron oxide- phosphorus magma derived from magmatic differentiation of primary mafic magmas and ascended to higher levels through faults and fractures. Oxygen and hydrogen isotopic study of quartz along with magnetite ore in this deposit and calculation the fluid equilibrium with it shows that the ore- bearing fluid has a magmatic origin.

The Narm iron mine located in the north of Tabas, the South Khorasan province in the north east of Iran. Magnetite is the main mineral, is associated with actinolite as the most abundant silicate mineral as well as apatite as the micro crystalline localized aggregations in the mineralization zone. The iron ore grade ranges from 50 to 55 wt% and 3% sulfur content. On the base of field observation, geochemical investigation, the rare earth elements pattern and their distribution there are many similarities between the mineralization of Narm mine and some magnetite-apatite iron oxide (IOA) deposits. Lithologically, the area mainly includes limestone-dolomite units of the Rizu formation in which gabbroic-dioritic magma is intruded. The dominant texture of these intrusive rocks is hypidiomorphic granular, dominated by plagioclase, amphibole (hornblende), pyroxene (mostly diopside), apatite as an important accessory mineral and opaque minerals mainly magnetite and pyrite. The rocks under study are alkaline in nature formed in within plate zone. These gabbroic-dioritic rocks were produced as a result of low degree partial melting of mantle wedge with garnet lherzolite composition. Any geochemical evidence indicating of crustal contamination is not observed. .

Olivine basalts from east of Nehbandan and Chahchocho regions belong to sodic alkaline and transitional magma series. Compared to alkaline olivine basalts (AOB), the transitional olivine basalts (TOB) have higher MgO, SiO2</sub>, Ni, Cr, Ba, Th, Pb, and U, and lower TiO2</sub>, FeOt</sub>, REE, and HFSE. High MgO, Mg#</sup>, Ni, and Cr (13.8 wt%, 77, 531 and 860 ppm, respectively) of the TOBs indicate that their chemical composition is close to a primary magma in equilibrium with mantle peridotites, whereas, the same values of the AOBs (8.3 wt%, 59, 155 and 176 ppm, respectively) are not quite close to a presumed primary magma. Based on petrographic and geochemical criteria, the TOBs have undergone both crystal fractionation and crustal assimilation, but the AOBs just show evidence of fractional crystallization. The enrichment of all rocks in the LREEs compared to the HREEs, LILEs relative to the HFSEs, together with the REE and multi-element patterns close to those of OIB may be indicative of an enriched asthenospheric-lithospheric mantle source. Non-modal batch melting models show that the AOBs are generated by ~7% partial melting of an asthenospheric mantle source at garnet lherzolite stability field. Furthermore, the TOBs are formed either by 7-15% partial melting of a metasomatized lithospheric mantle, or they are products of partial melting of an asthenospheric-lithospheric mantle source at 50% garnet-50% spinel lherzolite stability field.