Document Type : Original Research Paper

Authors

• A. Saki ¹
• M. Moazzen ²
• M. Modjtahedi ²
• R. Oberhänsli ³

¹ Depatrmant of Geology, Shahid Chamran University, Ahvaz, Iran Depatrmant of Geology, University of Tabriz, Tabriz, Iran

² Depatrmant of Geology, University of Tabriz, Tabriz, Iran

³ Institut fur Geowissenschaften, Universität of Potsdam, Germany.

Abstract

    Mahneshan Complex in the northwest of Iran was affected by regional and contact metamorphism. Microstructural and petrographical features as well as field relations show that Mahneshan Metamorphic Complex has been affected by four episodes of metamorphism (M₁ to M₄) and at least two deformational phases (D₁ and D₂). The M₂ metamorphic stage is characterized by a strong preferential orientation of minerals (S₂) and development of a peak metamorphic assemblage. This metamorphismis temporally associated with D₂ deformational phase. The M₃ metamorphism was contact metamorphism and M₄ metamorphism is retrograde. The mineral assemblages of peak metamorphism M₂ are muscovite, biotite, garnet, staurolite, andalusite and sillimanite.  Pressure and temperature of metamorphism in the Mahneshan Complex were estimated by multiple equilibria calculations, cation exchange reaction thermometry and net transfer reaction in order to determine the geothermal gradients and type of metamorphism. The temperature of M₁ metamorphism is estimated 420-450ºC and pressure of 3-4 kbar. M₂ (peak metamorphism) temperature is 600-620ºC and pressure of 5-7 kbar. The temperature of M₃ metamorphism is 520-560 ºC and pressure of 2.-3.5 kbar. The Geothermal gradients for the peak of metamorphism show high value for the upper crust (33° C/ km) indicating a Barrovian type of metamorphism for the study area. Tectonic setting of metamorphism is related to continental crust and magmatic arc.

Keywords

• Geothermobarometer
• Mahneshan Complex
• Geothermal gradient
• Cation exchange reactions
• Metapelites

20.1001.1.10237429.1387.17.68.8.1