Abstarct: The studied area is located in the

 Km of the N-NE of Semnan in the end of central Alborz structural zone. Sedimentary, Igneous and mextamorphic rocks are the main rocks us this area. Igneous outcrops include gabbros and granitoids. Nokeh granitoides contain mainly granodiorite and alkali feldspar granite. Igneous plutons of Attari area have granites and monzogabbroic compositions.Quatrz, plagioclase and k-feldspar are essential rock forming minerals of the granites. Biotites, green hornblende, sphen and opaque minerals are the other rock forming minerals of the gabbros. Granitic rocks show the granular, graphic, myrmekitic and perthite textures. Plagioclase, augite and olivine are the essential minerals of gabbros. Chlorite, epidote and calcite are the secondary minerals of gabbroic rocks. Gabbros show granular, intergranular and ophitic textures. Plotted geochemical diagrams on the baxse of major and trace elements of the studied rocks indicate that there is no a magmatic and genetic relation between gabbros and granites and also they originated from the same magma source regions. With attention to field, petrography and geochemistry investigation, gabbros originated from melting of an enriched mantle and the granitic rocks originated from melting of lower crustal igneous rocks. Granites rocks have mextaluminous to weak peraluminous nature and belong to I type granitioids of continental volcanic arcs. mextasomatism process along the contact of granitoids rocks with host rocks is resulted to form iron skarn. Skarnization(ingeneral concept) and producing garnet-megnetite-diposide paragenesis and scapolitizating in the alkali-feldspar granites and their tuffaceous host rocks. Contact mextamorphism progressed to pyroxene hornfels facies and maximum P-T condition is :  º C temperatures and about 2 Kbar.