Writers : Nimroozi, A.; Moaf Poorian, Gh. A.; Haghighat, N.
Refference : 28th Symposium on Geosciences and the 14th Symposium on Geological Society of Iran
Publishing Year : 1388

Abstract :

The aim of this research is studying of Ultramafic rocks at the northeast of Iran, as a series of scatter out crops along the northeast margin of Torbat -e- Jam - Fariman. Ultramafic rocks are seen as brecciated and or pillow to massive lava with aphanitic texture, so it is obvious their volcanic origin.Disequilibrium textures which are seen in microscopic studies are due to rapid growth of crystals due to undercooling of melts which were superheated or, at least, were hotter than normal basic magmas. Another important petrography observation in ultramafic rocks is presence of spinel crystals between olivine and clinopyroxene crystals that favor late crystallization of spinel, after olivine and which is characteristic of melts with very low content of water. High content of Ca in olivine crystals demonstrate that they aren’t xenocrysts related to mantle rocks disintegration, indeed they have to be crystallized from an ultramafic melt in volcanic to subvolcanic conditions and their Mg number must be a reliable criteria for approximation of temperature and MgO content melt. Computed temperature of melt, on the basis of maximum Mg number, is too high to coincide with generation of magma in mid oceanic ridge or subduction environments and is more similar to high temperatures observed in hot spot tectonic settings.