PETROGRAPHY AND MINERALOGY STUDY OF PYROXENITE AND WHERLITIC DIKES IN NAIN OPHIOLITE,CENTRAL IRAN

Various petrological facies of the northern Nain Ophiolite include serpentinized peridotite, mantle peridotites type harzburgite, dunite pods, peridotites type cumulate (plagioclase bearing harzburgitic dikes), wherlite and pyroxenite dikes, isotrophic gabbros, pegmatite gabbro dikes, diabasic sheeted dike complex, isolated diabasic dikes swarm dikes, pillow basalts and sheet flows. The relationship of these rocks is related to Tertiary tectonic sedimentary units which are directed on Akhoreh Formation flysch sediments aged Eocene as well as conglomerate sediments, marn and Miocene sandstone in the North East part of Nain. Red cherts which are located in an allogenic manner on the serpentinized peridotite as well as on microgabbroic dikes and sometimes between pillow basalts have also radiolarian facies and belong to the late cretaceous. Schistose limestones of the late cretaceous are also located in an allogenic manner on the ophiolite units.

Peridotite dikes ( wherlite )and pyroxenite dikes with webstrite to olivine webstrite compound have sometimes cut off the isotrophic gabbros and sometimes sheeted dikes of northern Nain ophiolite. wherlitic dikes are often changed into serpentinite with cross-linked texture. Olivine webstrite texture is granular and there is clinopyroxene, orthopyrxenite and a little chloritized and serpentinized olivine in their mineralogy compound. webstrite have also a granular texture and their mineralogy compound constitutes clinopyroxene and orthopyroxene. In these rocks first orthopyroxene has been formed and then subhedral clinopyroxene crystals were formed in the remaining space. Orthopyroxenes have sometimes changed into talc and chlorite, and sometimes to amphibole and talc in the directions of the fractures.

The average chemical compound of clinopyroxene type augite in the pyroxenites cutting isotrophic gabbros is En_50.617 Fs_7.26 Wo_42.123, and in pyroxenites cutting sheeted dikes is En_52.271 Fs_6.24 Wo_41.489.

The average chemical compound of orthopyroxene type enstatite in the pyroxenites cutting isotrophic gabbros is En86.388 Fs_10.661 Wo_2.951, and in pyroxenites cutting the sheeted dikes is En_89.052 Fs_7.989 Wo_2.96.