---

Diabases, pillow lavas and basaltic flows in the Nain-Dehshir ophiolites are marked with flat to slightly depleted pattern in REE chondrite-normalized diagram and are characterized by depletion in HFSE and enrichment in LILE. This geochemical behavior can be considered for lavas erupted in arc-related environments. Clinopyroxene in these rocks shows low content of TiO₂ and resemble those found in island-arc tholeiites. These characteristics are consistent with back-arc formation during middle to upper Cretaceous, due to the oblique subduction of Neotethyan Ocean along the active continental margin of the central Iranian block.

---

The Kamyaran ophiolite complex as a part of the Kermanshah ophiolite is located in western Iran, along the Zagros orogeny and Neotethys suture zone. The Kamyaran ophiolite complex includes serpentinized harzburgites, isotropic and layered gabbros, diabasic dykes and pillow basalts. The diabasic dykes have experienced upper green schist facies metamorphism. Based on mineral chemistry of the diabasic dykes, plagioclases are oligoclase to andesine and clinopyroxenes are diopside in these rocks. Tetrahedral site is occupied completely by Si and partially by Al (AlIV) in the clinopyroxenes. Oxygen fugacity during crystallization of the diabasic dykes magma, calculated using crystallization composition, points to effects of subduction process on diabasic dykes of the Kamyaran ophiolite complex. Clinopyroxene crystallized at less than 5 Kbar pressure in the presence of almost 2.5 percent H2O. Chemistry of clinopyroxenes indicates IAT characteristics for the original magmas, showing a supra-subduction environment for generation of the Kamyaran ophiolites.

---

In Reza-Abad area (E- Shahrood city), diabasic dikes swarm (gabbro / diorite) with trends east-west intruded into Pre-Cambrian igneous - metamorphic complex of Central Iran Zone. These rocks display intergranular, ophitic and subophitic textures. Clinopyroxen (augite to diopside), plagioclase (oligoclase-andesine and labradorite- bitonite) and amphibole (magnesia hornblende) are the main minerals. Apatite, sphene and magnetite are accessory minerals. Based on the combination of clinopyroxene, primary magma of basalts has alkaline nature and were formed within-plate setting. The Clinopyroxene thermobarometry determines a temperature of 1100-1200 °C and pressures 1 – 10 Kbar with a density in 4-8 Kbar. Based on these results, crystallization of clinopyroxenes begins in the magma chamber at depth of 25km, this depth is at equilibrium with middle crust.

---

The studied diabase rocks of the Hormuz Formation have undergone a variety of secondary processes and greenschist facies to amphibolite facies metamorphism. These rocks are metasomatized due to the effect of infiltrating metasomatism and hydrothermal alteration and are metamorphed due to CO₂-rich aqueous fluids and rock-fluid interaction. Feldespat, pyroxene, olivine, apatite, rutile, magnetite and pyrite are the primary magmatic minerals present in these rocks and other minerals, are products of the transformation of the primary minerals due to metasomatism and thermal metamorphism. Feldspars are labrador, albite and orthoclase. Labrador and albite were crystalized at tempretures of <700 and pressures of <6 kbar which is their recrystallization tempreture. Orthoclase was crystalized at tempretures and pressures of 700, 6 kbar and >1000, >7 kbar and is a magmatic mineral. Clinopyroxens are augite and diopside and were crystalized at 1100 to 1300 and are magmatic minerals. Pyroxenes are subalkaline to alkaline and were formed within plate tholleitic basalt or oceanic floor basalt environment. Plagioclase and pyroxene minerals show oxidation conditions. According to the analyzed zircons from Band-e Moullem (539/4 ± 6/4 Ma) and Champeh (543/5 ± 6/1 Ma) salt dome diabase, these rocks have been crystalized and formed during Early Cambrian time. In addition, most of these zircons have a magmatic origin. This estimated age suggests that the intrusion of these diabase, occurred during and/or after the Neoproterozoic to Early Cambrian rifting of the northern part of the Arabian plate and the sedimentation of the Hormuz Formation in the Persian Gulf Basin.

---

The Hormuz Formation is a sequence of lithologically various evaporitic–volcanic rocks in salt domes where the volcanic rocks are dominantly acidic, generally with less than one third basic volcanics. It was formed in the Late Proterozoic (640–620 Ma)/Neoproterozoic–Early Cambrian, as a result of sub-basin rifting in the northern part of the Arabian plate, throughout most of the Persian Gulf Basin and the equivalent Ara salt in Oman. Diabase is the most common basic rock of the Hormuz Formation. In the field, the studied diabases are seen as stock-like outcrops and dykes which are extremely altered. These rocks contain plagioclase, pyroxene and less olivine as primary minerals which are transformed to various secondary minerals and the diabases primary textures are ophitic, porphyritic and microlitic flow. 22 samples of these diabases from 7 salt domes of southern Iran were analyzed by XRF and ICP-MS methods and then studied. On geochemical diagrams, these rocks plot in the field of tholeiitic basalts and mid-oceanic ridge basalts (MORB). According to values of major and rare elements, these diabases have undergone fractional crystallization within a magma chamber or en route to the surface. Due to REE pattern and values of these samples, the parental rock of the magma which produced them has experienced intermediate degrees of partial melting and these diabases have undergone low degrees of crustal contamination during magmatic evolution. According to values of rare elements ratios, they were probably generated from a depleted to transitional mantle source derived from a garnet-free, spinel peridotite source region. Therefore, the Hormuz Formation diabases are products of the Neoproterozoic to Early Cambrian rifting of the northern part of the Arabian plate. They have similar chemical compositions as Archean tholeiitic basalts and show all the features of a greenstone but whether or not they are on a Phanerozoic greenstone belt, needs further tectonic studies.