Author(s)

Zahra Shafeie¹, Mohammad Ali Arian^1*, Shahrouz Haghnazar², Mansour Vossoughi Abedini³

¹Department of Geology, Faculty of Science, North Tehran Branch, Islamic Azad University, Tehran, Iran.
²Department of Geology, Faculty of Science, Lahijan Branch, Islamic Azad University, Lahijan, Iran.
³Department of Geology, Faculty of Science, Science and Research Branch, Islamic Azad University, Tehran, Iran.

In the Alborz Mountains of the eastern Roodbar (north of Iran), Tertiary volcanic rocks have a variety of composition between olivine basalt, basaltic andesite, pyroxene andesite and andesite. The presence of different xenoliths and xenocrysts is among the evidence of crustal contamination of these rocks. The positive correlations of CaO/Al₂O₃ vs to MgO and Al₂O₃ vs. SiO₂ are of signs of the olivine and clinopyroxene fractionation in the variation trend of the area rocks. Positive correlations K₂O/P₂O₅ vs with SiO₂ and La/Sm vs. K₂O/P₂O₅ demonstrate contamination of magma with the continental crust. The incompatible trace element patterns and their comparison with crustal contents indicate contamination of the rocks of the area with the lower and upper continental crust. Linear trends in the variation diagram of Nb/Y vs. Zr/Y, introduce two different source regions: a MORB source and the other continental crust for the rocks which are the genesis. The variations of Y/Nb vs. Zr/Nb and Rb/Y vs. Nb/Y reveal a crustal contamination of the magma originated from the MORB source. Geochemical studies represent that the area’s rocks were derived from the 15% melting of a mantle source of MORB type with spinel facies within a continental environment, which was contaminated by varying degrees of continental crustal rocks.

Volcanic Rocks, Tertiary, MORB Source Mantle, Crustal Contamination

Shafeie, Z. , Ali Arian, M. , Haghnazar, S. and Abedini, M. (2016) Geochemistry and Petrogenesis of Tertiary Volcanic Rocks of the Eastern Roodbar, Alborz Mountain, North of Iran. Open Journal of Geology, 6, 1296-1311. doi: 10.4236/ojg.2016.610095.