Mineralogical features of amphibole in the Mashhad amphibole-peridotites

The Mashhad ultramafic complex with a Permo-Triassic stratigraphic age is exposed at the NE of Binaloud Mountain and the SW to NW of Mashhad city. This area is mainly composed of mafic and ultramafic rocks, metamorphosed carbonate and pelitic rocks and granitoids in a NW- SE trend. Serpentinized amphibole-peridotites are the main types of ultramafic rocks in this area. Minerals in these rocks include olivine, orthopyroxene, clinopyroxene, brown amphibole and opaque minerals as the original minerals and serpentinite group minerals, tremolite, actinolite, chlorite, talc and carbonate minerals are the secondary minerals. The amphiboles are commonly of two types. One comprises brown to red-brown subhedral pargasites. The second type is seen as colorless or pale green unhedral tremolite-actinolite. Variations in the cation proportions of Al, Fe, Cr and Ti in structure of amphiboles are strongly influenced by adjacent minerals (e.g. olivine and pyroxene, especially iron-bearing phases such as chromite). Petrographic (textural relationships between minerals) and mineral chemistry data indicate that the pargasites in amphibole-peridotite in the study area compatible with metasomatized mantle peridotites in a subduction zone.