MAGMATIC FRACTIONATION MODELLING IN KARAJ DAM SILL IGNEOUS ROCKS

At the NE of Baraghan, Karaj Dam Sill, intruded between the pyroclastic rocks of Karaj formation. The composition of the Sill changes from gabbro and monzogabbro to monzodiorite. Based on field observations and microscopic studies, the sill was differentiated from margin to center. For geochemical modeling in study area, incompatible elements diagrams such as Zr vs. Rb and Ba vs.Ce have used that sample^, s trends are consistent with Fractional Crystallization (FC) process vector and maximum fractionation percentage for samples with high SiO2(65%) are 80%. For determining differentiated mineral and differentiation percentage have used mineral vector diagrams such as Logarithmic bivariant diagram Ba,Sr. results show that samples was formed by Plagioclase, Clinopyroxene and olivine fractionation. Also based on fractionation vectors and numerical modeling, fractionation ratio for this minerls are approximately (pl/cpx/Ol,55:35:10).

Modeling results shows that Magmatic crystallization based on Rayleigh fractiontion Equation can explained chimecal variations of trace elements. Although not following some elements from fractionation process trend in some samples (like unusual enrichment Ba) show that other process like crust contamination and secondary process like hydrothermal alteration can play important role in chemical variance of elements in study area.