Original paper

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

Khalili, Khadijeh; Torabi, Ghodrat; Arai, Shoji


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.


ophiolitepaleo-tethyslherzolitecentral iranposht-e-badamperidotiteamphibolitemetamorphism