Petrography & Petrology of Metamorphic RocksSouth of Soltanabad (Sabzevar)

Abstract:
      Besides ophiolitic naps, spilitice lavas and oceanic sedimentary (limestone ? radiolarite) outcropped as belt almost eastern-western between Sabzevar and Soltanabad(north of Khorasan) at Upper Cretaceous(87Ma). This complex is thrusted upon Quaternary-Upper Tertiary sedimentary and mostly covered by these rocks in the north. A metamorphic sole with 23 km length and 2 to 4 km width is outcropped almost eastern- western trend in the northern marginal of ophiolitic nap and it's sedimentary and several granitoidic, tonalitic, gabbroic bodies and basaltic dykes is seen within it. The part of metamorphic consists of slate, micaschist, calcschist, blueschist, greenschist and amphibolit. The chemical composition of amphibolits are mostly transitional basalt, tholeitic and seldom calc-alkaline. Metamorphic rocks (except intrusion bodies) have metamorphosed at least two phases: primary is dynamothermal (plus intense deformation) and secondary is static (without changing in structures) while intrusion bodies have just suffered second stage of metamorphism. Metamorphic conditions have been quite high pressure ? low temperature (lower blue-schist facies) in the first stage and isotrope pressure and quite high temperature but accompanied by metasomatism in the second. Albite+ epidot+ actinot + muscovite paragenesis belongs to second metamorphic stage and observed in the whole rocks (schist, amphibolite, gabbro and granitoid). Radiometric age of last stage has gained 52 to 54 Ma years. According to composition of metabasits protolith, it looks that these rocks have belonged to a series of island arcs and have undergone dynamothermal metamorphism, time of central Iran?s collision with Turan block (probably at the Upper Cretaceous) and then have been suffered isotrope pressure- quite high temperature metamorphism as the result of oceanic crust abduction of a back-arc basin (north to south) in the Middle Eocene.