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.