Investigating the volcanic rocks petrology in Farmahin area of Arak

Category Petrology
Group GSI.IR
Location 20th symposium on geosciences
Holding Date 16 April 2008

     Farmahin area is a small part of theUromyieh-dokhtar structural zone .This area is located in the north west of Qom sheet (scale
1:250000). These studied rocks are belonging to the middle and
upper Eocene.
The lavas composition of this period includes andsybasalt,andesite ,trachyandesite,ignimbrite and rhyolite.The most texture of these rocks include porphiritic ,mega porphiritic ,and porphiroclastic. The plagioclase ,pyroxene and biotite are the mainly minerals and accessory mineral are zircon,apatite and opac minels.Microscopic studied of these lavas demonstrated evidences of magmatic contamination in osciliatary zoning in plagioclases shapes ,and also traces of corrosion in plagioclases and formation of basic micro pillow.
The geochemical diagrams of the said rocks are presented with a nature to caic-alkaline and a tendency to potassic.The position of the samples on the elements of the major diagrams on comparision to differentiation coefficoent demonstrated positive and logical linear trend of differentiation magmatic (MgO-DI,CaOD1)although on digrams of(Na2O-DI,K2O-Dl)there is seen a little scattered ,that it may probably be related to the unhoogene source of magmatic ,alteration variety degrees of partial melting, crustal contamination and metasomatism.On the diagrams of the REE(La,Sm)elements and HFS(1 If,Ta)LFS(Sr,Ba)elements on comparision to differentiation coefficoent there is seen some scatte and anomaly that can be subjected to the results of the area by amphibolite-geniss facies(upper crust) which presents the source magmatic contamination.
It appears that two processes of partial crystalization and par