The Takab meta-ultramafic rocks of northwestern Iran crop out in association with a variety of metamorphic rocks and they can be divided into three types on the basis of dominant mineral assemblage and degree of serpentinization: metaperidotites, talc-serpentine rocks and serpentinites. The peridotite protoliths were mainly spinel-harzburgites and -dunites. The talc-serpentine rocks formed under low-grade conditions and their dominant mineral assemblage is lizardite/chrysotile + talc + calcite/dolomite. Pseudomorphic textures after olivine and pyroxene are typical. Later, lower amphibolite-facies metamorphism produced antigorite, clinochlore and tremolite. Late alteration, assisted by local shearing, produced more antigorite and late lizardite in the metaperidotites. The mineral chemistry of the serpentine polymorphs is variable. Compositions of coexisting spinel and olivine point to an ophiolitic origin. Thermometric estimates from co-existing relict olivine, pyroxenes and spinel are in the range 1000–1200ºC; clinopyroxene barometry yields a pressure of 24± 2.7 kbar for the mantle conditions. Exhumation and hydration followed, and the stability of lizardite/chrysotile constrains the T and XCO2 to <280ºC and <0.002, respectively. Subsequent prograde regional metamorphism took place in an orogenic setting, reaching peak temperatures in the range 410–540ºC at XCO2 >0.1. A Neoproterozoic–Early Cambrian age for the Takab protoliths is suggested on the basis of correlations with the Central Iran Zone. The strips of ultramafic rock in the Takab complex can be attributed to lithospheric remnants of the Proto-Tethyan ocean which closed during the Pan-African orogeny.

The Poshtuk metapelitic rocks in northwestern Iran underwent two main phases of regional and contact metamorphism. Microstructures, textural features and field relations indicate that these rocks underwent a polymetamorphic history. The dominant metamorphic assemblage of the metapelites is garnet, staurolite, chloritoid, chlorite, muscovite and quartz, which grew mainly syntectonically during the later contact metamorphic event. Peak metamorphic conditions of this event took place at 580 °C and ~3–4 kbar, indicating that this event occurred under high-temperature and low-pressure conditions (HT/LP metamorphism), which reflects the high heat flow in this part of the crust. This event is mainly controlled by advective heat input through magmatic intrusions into all levels of the crust. These extensive Eocene metamorphic and magmatic activities can be associated with the early Alpine Orogeny, which resulted in this area from the convergence between the Arabian and Eurasian plates, and the Cenozoic closure of the Tethys oceanic tract(s).