Miss Khadijeh Heidari, Dr Mohsen Nasrabadi, Dr R Nozaeem, K Gholizadeh,
Volume 2, Issue 1 (7-2016)
Abstract
There are small plagiogranite intrusions and veins in the ophiolitic complex of Northern Kamrod and Southern Dehshir containing feldspar+quartz+biotite±garnet minerals. The host rock of plagiogranites are granular and foliated metagabbro. Ragged boundary and partial replacement of pyroxene by amphibole in the massive metagabbros indicate a disequilibrium state and metamorphic origin of amphibole. In the foliated metagabbro unlike granular ones the relicts pyroxene is absent. Whole rocks geochemical evidences imply partial melting as the main process in generation of plagiogranites in a slow-spreading center of suprasubduction setting. Probably water infiltration through fractures of a spreading setting of back arc resulting of Neotethys subduction caused hydrothermal metamorphism and hydration of ophiolitic sequence gabbros, partial melting and creation of plagiogranitic melt. Alternatively it is possible that during injection of hot magmatic bodies, amphibole dehydration, partial melting and generation of plagiogranitic melt have been occurred as well. On the basis of chemical composition of clinopyroxene, crystallization temperature of gabbroic cumulate is determined between 959 to 977°C. Pressure and temperature conditions of hydrothermal stage estimated as less than 3 Kb and 750°C, owing to chemical composition of metamorphic amphibole. Based on whole rock geochemical signatures of the plagiogranites and their comparison with experimental results, the partial melting temperature is calculated as less than 850ºC. The latest stage of hydrothermal metamorphism was associated with prehnite formation under shallow conditions.
Fatemeh Nouri Sandiani, Dr Hossein Azizi,
Volume 3, Issue 2 (12-2017)
Abstract
Some Peridotite dismembered parts have outcropped in Southwest of Sahneh, as a part of Zagros ophiolite complex. These bodies contain olivine, pyroxene and spinel with some altered minerals such as serpentine and amphibole. Based on electron microprobe analyses, olivine composition is forsterite with Fo88-94. The composition of pyroxenes is diopside and clinoenstatite with low contents of TiO2 and Al2O3. The spinels are poor in Al2O3 with Cr# number between 0.41-0.51 which indicate the ophiolitic and depleted mantle origin. The serpentines have Al2O3 content in the range of 0.2 to 2.2 wt.% with SiO2 content between 34.15 to 44.07 wt.% and are chrysotile and lizardite. The low temperature of serpentine minerals (lizardite and chrysotile) and primary spinels indicates that the alteration was lower than 500 ºC. In the tectonic setting diagram, based on mineral chemistry, the higher content of Al2O3 and MgO in pyroxenes than to mid oceanic ridge ones and have the same properties with back arc basins. These evidences have been confirmed by spinel mineral chemistry. Accordingly based on the geodynamic situation of Kermanshah area and tendency of some samples to back arcs, it seems these peridotites have derived by high degree partial melting of depleted and sub-oceanic mantle in a supra-subduction zone-back arc and have same properties with residual mantle peridotites
