Garnet composition from felsic pegmatitic rocks in North of Golpayegan (Ochestan), Iran

The felsic pegmatitic rocks are exposed in the north of Golpayegan. The dominate mineral assemblage is quartz, K-feldspar, plagioclase, muscovite, tourmaline and garnet. The elevated spessartine content of the garnets in the studied rocks along with their idiomorphic shape, the absence of resorption feature and garnet-free country rocks may point to their magmatic origin and crystallization at a fairly low pressure (less than 3 Kbar). A significant geochemical criteria is the absence of chemical zoning which suggest their crystallization at temperatures above ∼ 700 °C. Apparently at these temperatures, the Mn diffusion becomes sufficiently rapid to eliminate compositional zoning. The overall petrographical and geochemical data indicate that these phases generated from peraluminous S-type melts.