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Geochemistry and geochronology of amphibolites from the Sirjan area, Sanandaj-Sirjan zone of Iran: Jurassic metamorphism prior to Arabia and Eurasia collision

2020; Elsevier BV; Volume: 143; Linguagem: Inglês

10.1016/j.jog.2020.101786

1879-1670

Hadiseh Rahimi Sadegh, Hesam Moeinzadeh, Mohssen Moazzen,

High-pressure geophysics and materials

Mesozoic ortho-amphibolites exposed in the SE Sanandaj-Sirjan metamorphic belt (Bahram-e-Gur area, south-central Iran), record medium to high-grade metamorphism. Based on mineral assemblages, three lithological types of amphibolites have been defined: plagioclase amphibolite, epidote amphibolite, and biotite amphibolite. Metamorphic geothermobarometry reveals temperatures of 548−710 °C at 3–6 kbar, corresponding to a geothermal gradient of ca. ∼28 °C/ km, for the peak metamorphism. 40Ar/39Ar stepwise heating analyses, performed on amphibole separates revealed a well-defined isochron with a cooling age of 169.35 ± 14.77 Ma and a plateau cooling age of 162.54 ± 1.97 Ma (Upper Jurassic). The protoliths of the studied amphibolites were basalts, which were formed in an active continental margin tectonic setting, due to an extensional regime, brought about by a probable steep slab subduction. The magma affected by crustal component, acquired calc-alkalic characteristics. The rocks were metamorphosed in a compressional event due to flat subduction following a steep slab subduction. The age of metamorphism was pre-Middle Jurassic (older than ca. 162 Ma). Similar age metamorphic and magmatic events in the Sanandaj-Sirjan zone indicate that peak metamorphism and magmatic cooling were chronologically close. The studied rocks are related to Jurassic compression at the southwest active continental margin of the Central Iranian microcontinent and early Cimmerian deformation and metamorphism in the southeast Sanandaj-Sirjan zone.