Metamorphism of peridotites from Posht-e-Badam Paleozoic ophiolite Yazd Province, Central Iran

Abstract

The Posht-e-Badam ophiolite is situated in the Central-East Iranian Microcontinent CEIM and central domain of the Posht-e-Badam Block. This ophiolite of Paleozoic age is a remnant of the Paleo-Tethys ocean. The rock suite comprises metamorphosed peridotites, metagabbro, ampbibolite and listwaenite. Peridotites form the most important rock types of the Posht-e-Badam ophiolite and metalherzolites are the least altered metaperidotite. They are closely associated with amphibolites and cover Paleozoic metasedimentary rocks schist and marble. Rock-forming minerals of metalherzolites are olivine chrysolite; Mg# = 0.80, tremolite average MgO and CaO content 23.31 and 12.88 wt%, respectively, chlorite penninite; Mg#~0.92, serpentine, chromian magnetite, magnetite and calcite. The main textures of these metamorphosed lherzolites are porphyroblastic, granoblastic, nematoblastic, poikiloblastic, jack-straw and mesh texture. Metamorphic mineral assemblages in the metaperidotites, mineral chemistry of amphibolites, together with regional geologic constraints, led to the conclusion that the Posht-e-Badam partially serpentinized peridotites M1 were metamorphosed under lower amphibolite-facies conditions M2, which was followed by a retrograde stage of metamorphism under greenschist-facies conditions M3. The maximum temperature of regional metamorphism M2 was not sufficient to replace calcic amphibole tremolite by calcic pyroxene. The presence of magnetite inclusions in the olivine neoblasts reveals that the studied metalherzolites were partly altered M1 before being progressively metamorphosed under lower amphibolite-facies conditions M2. Latestage retrograde metamorphism M3 led to partial serpentinization of metamorphic olivine and partial replacement of tremolite by chlorite. These three metamorphic episodes can be attributed to, respectively, the Early, Middle and Late Cimmerian orogenies of Central Iran. © 2016 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany.