پترولوژي پريدوتيت هاي گوشته افيوليت ملانژ نايين

Petrology of Mantle Pcridotites in Naein Ophiolitic Melange

The abundance of peridotite rocks in Naein ophiolite is about of 70 percent of melange. The studied rocks are mantle peridotites of an oceanic lithosphere that have been emplaced in north of Naein in Late Cretaceous to Early Tertiary time. The petrographic and field studies, with mineralogical comparison of lherzolite, harzburgite and dunite, show transitional changes of lithology and mineralogy. The applied geothermoeters and barometers show that olivine-spinel equilibrium temperature in lherzolite is 730 and in harzburgite 778°C, but in contrast two pyroxene crystallization temperatures obtain 1092°C for lherzolite and 1219°C for harzburgite. Field and petrographical studies and difference between obtained temperatures by applied geothermometers and increasing trend of olivine-spinel geothermometry from lherzolite to dunite, reveal the melt/mantle reaction. Moreover, chemical analysis of spinels and olivine show that Cr# of spinels increase fromlherzolite to dunite, but the Mg# of coexisting olivines decreases. This negative correlation in mentioned factor has been formed by increasing of the replacive olivines during melt/mantle reaction and incongruent melting of orthopyroxenes. Consequently, studied rocks are tectonites that have been affected by melt/mantle interaction.