Mineral chemistry and whole rock geochemistry evidences of the differentiation in the Karaj Dam basement igneous rocks

Igneous rocks of the Karaj Dam basement are mainly composed of gabbro, diorite and monzodiorite-monzonite which are locally penetrated by the quartz-monzonitic dikes. The upper and lower margins of the pluton, which has gabbroic composition, show porphyritic texture (chilled margin). The porphyritic texture in chilled margin gradually changes to the equigranular gabbro, diorite and monzodiorite-monzonite. The mineral chemistry (electron microprobe analysis) of the plagioclase and pyroxene in various rock samples from lower contact chilled towards the upper parts suggesting differentiation processes. The Mg of the pyroxene and An% of plagioclase of the contact chilled samples can be used as an indication of the original magma and plotted between the gabbro and monzonitic samples. In addition, increasing of the Mg within the whole rock samples from the upper of contact chilled, in comparison to the lower one, suggests elements differentiation by the gravity diffusion. Moreover, Na2O, K2O and incompatible elements increase and MgO, Fe2O3 (tot), CaO and compatible elements decrease with the progress of the magma differentiation. The samples in the Log Ni-Log La and Log Ni-Log Zr diagram plot almost as straight horizontal line, which confirms occurrence of the magma differentiation.