سنگ‌شناسی و ژئوشیمی گرانیتوئیدهای هولولوکوکرات توده‌ی گرانیتوئیدی الوند (همدان)

Hololeucocratic granitoids of Alvand main granitoids crops out as veins with low thickness. They are scattered in the south and west of Hamadan with latitudes of 34° 30´- 35°00´ N and longitudes of 48°00´- 48° 45´ E. This granitoids, based on petrological studies, are in the ranges of leucotonalite, leucogranodiorite and leucoquartz- monzodiorite. The investigation, based on the grain size, show that hololeucocratic granitoids can be divided into two groups: 1) coarse- graind and 2) fine- graind. Sharp contact between hololeucocratic granitoids and Alvand main granitoids indicate that hololeucocratic granitoids are younger than main granitoids (Paleocene to Late- Paleocene). Mineralogical and geological studies show that they are I- type, alkaline-calc and based on saturation degree of aluminum (ASI), they are metaluminous to slightly peraluminous. These granitoids enriched in Sr and depleted in Ba, Rb, Nb and Ti which are obvious in the spider diagrams. They are also poor in K2O, FeO, MgO and enriched in CaO, Na2O with respect to Alvand main granitoids. These rocks show enrichment from LILE and LREE elements and are depleted from HFSE elements. These properties are an indication of   subduction zones and active continental margins.The Rb vs. Ta + Nb, Nb vs. Y, Rb vs. SiO2 geotectonic affinity discrimination diagrams support an I- type, volcanic arc environment for the hololeucocratic granitoids of Alvand Complex. With regard to geological history of this area, it can be attributed to subduction of oceanic crust of Neotethys under the Central Iran.