بررسی سنگ‌شناسی و ژئوشیمی دایک‌های مافیک و فلسیک مجموعه پلوتونیک الوند- همدان و بررسی شیمی کانی‌های موجود در آنها

The Alvand plutonic complex is composed of various plutonic rocks, mafic and felsic dikes (pegmatites and aplites). Pegmatites and aplites consist of quartz, feldspar, mica, tourmaline, garnet and allanite. Based on the mineralogycal compound, pegmatites can be divided into tourmaline-garnet-muscovite-bearing, aluminosilicate-bearing and tourmaline-bearing pegmatites and aplites are composed of tourmalime – bearing, garnet – bearing, and tourmaline – garnet – muscovite-bearing pegmatites. Based on the geochemical properties, pegmatites and aplites can be divided into sodic and potassic groups. Harker and spider diagrams show that the pegmatitic and aplitic dikes are co-genetic and the mafic dikes and other mafic to intermediate rocks in this area are co-magmatic. The studied felsic dikes are peraluminius and calcalkaline. Mafic dikes are calc-alkaline to tholeiitic and meta-aluminous. Type of garnets in pegmatites are pyralspite )Sps61.5- Alm34.6-Grs3.1-Prp0.8( and plagioclase in pegmatites and aplites are (An2-5) and (An7-13), respectively. K-feldespars in pegmatites have intergrowth of albite up to about 50%. White mica in pegmatites and aplites plots between muscovite and celadonite. Biotites in aplites are of siderophyllite type and allanite in pegmatite is Ce-rich type. Based on geochemical studies, in spider diagrams felsic and mafic dikes and mafic host rocks show depletion of HREE and Zr, Hf, Y, Ti, Ta and Nb elements and enrichment of LIL (K, Rb, Cs) and LREE elementswhich indicate their formation in a subduction environment.