Petrological Journal

Study of mineral chemistry, thermobarometry and petrogenesis of migmatitic rocks of Hamedan area

Ali Asghar Sepahi Gerow; Seyedeh Razieh Jafari; Mohssen Moazzen; Hossein Shahbazi

Volume 9, Issue 1 , June 2018, , Pages 165-190

https://doi.org/10.22108/ijp.2017.103130.1026

Abstract

In the Hamedan region, migmatitic rocks occur with various structures. In the Simin area (South Hamedan) stromatic and in the Darreh-Omar (Toyserkan) area ophtalmitic structures are ... Read More In the Hamedan region, migmatitic rocks occur with various structures. In the Simin area (South Hamedan) stromatic and in the Darreh-Omar (Toyserkan) area ophtalmitic structures are abundant. Migmatites have been developed in a poly-metamorphic region. At least one regional metamorphism and two contact metamorphism by mafic and felsic intrusions occurred in the area. It seems that in the Darreh-Omar area contact metamorphism of mafic body leading to migmatization, But in the Simin area previous regional metamorphism and development of shear zones followed by contact metamorphism by felsic body. Therefore, in some areas, such as the Simin area, the migmatization may have occurred in more than one stage. These are consistent with recent geochronological studies of the Alvand plutonic body and surrounding metamorphic rocks. Index minerals of metapelites such as garnet (almandine), biotite (siderophyllite), staurolite, andalusite, sillimanite, kyanite, fibrolite, cordierite, plagioclase (andesine) and spinel (hercynite) are existing in these rocks. Field geology, petrographic and geochemical evidences suggest that different generations of staurolite, biotite and cordierite exist in metamorphic rocks of different grades in the Hamadan area. These minerals sometimes have been formed by progressive reactions and some other times from retrogressive reactions. A number of these phases have been formed at the peak of metamorphism and some others in later time. Based on thermometric cation-exchange method of garnet-biotite pair, using different calibrations, the obtained temperature using first-generation of biotites is 655 °C and temperature range of 529 °C for second-generation biotites. Cordierite-garnet thermometry indicates a temperature of 637 °C for related migmatitic rocks. In barometry with GPBQ system, calculated pressure for first-generation biotite is estimated to be about 3.9 kbar and for the second-generation biotite around 3.6 kbar.

Serpentinization of the Piranshahr peridotites: investigations on serpentine polymorphs and metamorphic evolutions of the metaperidotites

Mohsen Moazzen; Farzaneh Valinasab Zarnagh; Robab Hajialioghli

Volume 5, Issue 20 , January 2015, , Pages 71-90

Abstract

The study area is located in NW of Piranshahr town, Western Azerbaijan province. Based on the petrography, mineralogy and textural relations, the peridotites studied are classified ... Read More The study area is located in NW of Piranshahr town, Western Azerbaijan province. Based on the petrography, mineralogy and textural relations, the peridotites studied are classified into two groups: serpentinized peridotites and serpentinites. The second type, on the base of serpentine polymorphs and texture can be classified into three subgroups in turn: a) hydrated serpentinites which are characterized by low temperature serpentine polymorphs (chrysotile and lizardite), b) antigorite (high temperature serpentine polymorph) bearing serpentinites which formed at relatively high T and P conditions having interpenetrative texture and c) listwanitic serpentinites with brecciated texture containing of minerals as serpentine, chlorite and high amounts of carbonates. Distinguishing of serpentine polymorphs in the investigated rocks has been done using Raman spectroscopy and microprobe analysis. Formation of low-T serpentine polymorphs in the hydrated serpentinites are most likely related to the in-situ alteration of oceanic crust whereas antigorite in the metamorphic serpentinites is formed due to regional metamorphism during subduction and/or subsequent closure of ocean. Tremolite, clinochlore/picnochlore and Fe-rich spinel are coexisting minerals with antigorite. Temperature and pressure of the antigorite bearing serpentinites are obtained on the basis of equilibria reactions using THERMOCALC, as 550ÂºC and 7 kbar, respectively. On the base of olivine and pyroxene norm, the protolith composition of the Piranshahr metaperidotites is determined as harzburgite and less lherzolite. The high MgO and relatively low CaO and Al2O3 contents of the investigated rocks indicate ophiolitic characteristics of the Piranshahr metaperidotites. Considering the location of the Piranshahr ophiolites at the end of the northwestern part of the Zagros ophiolitic belt, it can be concluded that hydrated serpentinites and antigorite-bearing serpentinites are formed in relation with static oceanic floor alteration and subsequent dynamic metamorphism during subduction and/or closure of the Neotethys ocean, respectively.

Whole rock chemistry of Shahindezh metapelites, provenance and mineral parageneses

Monir Modjarrad; Mohsen Moazzen; Mohsen Moayyed

Volume 1, Issue 4 , March 2011, , Pages 73-88

Abstract

In order to identify the provenance of metasediments of the Shahindezh Metamorphic Complex (SMC), NW Iran, we have studied the bulk chemistry of the metapelites in the mentioned area. ... Read More

Introducing the Ghorveh fibrolites and their formation condition

Hadi Omrani; Mohsen Moayyed; Ahmad Jahangiri; Mohsen Moazzen

Volume 1, Issue 1 , June 2010, , Pages 1-10

Abstract

The metamorphic rocks of the Ghorveh area, southeast of Sanandaj, are classified as a part of the Sanandaj-Sirjan metamorphic zone. South of Ghorveh includes an assemblage of regional ... Read More

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Author = Moazzen, Mohsen

Study of mineral chemistry, thermobarometry and petrogenesis of migmatitic rocks of Hamedan area

Abstract

Serpentinization of the Piranshahr peridotites: investigations on serpentine polymorphs and metamorphic evolutions of the metaperidotites

Abstract

Whole rock chemistry of Shahindezh metapelites, provenance and mineral parageneses

Abstract

Introducing the Ghorveh fibrolites and their formation condition

Abstract