شواهد پتروگرافي، ژيوشيميايي و ايزوتوپي آلايش پوسته اي دربازالت هاي منطقهٔ جواهردشت (شرق گيلان)

The Petrographical, Geochemical and Isotopical Evidences of Crustal Contamination in the Javaherdasht Basalts (East of Guilan)

The Javaherdasht basalts have considerable outcrops in the north part of Alborz mountains in the east of Guilan province.The petrographical, geochemical and isotopical evidence is indicative of the contamination of the basalts with continental crust. The petrographical evidence such as corosion gulf and crenated margins in pyroxene phenocrysts and chemical composition difference between clinopyroxene phenocrysts margins with matrix clinopyroxenes suggest of crustal contamination and nonequilibrium due to the change of matrix composition as compared with pre-existed phenocrysts in rock .The depletion in elements such as Zr, Nb,Ti02 ,P205 and enrichment of LIL elements,high ratios of Pb/Nd and Ba/Nd,low content of Zr/Nb,Y/Nb,Ce/Pb, positive correlation between Si02 and 87 Sr/86Sr and positive correlatian between MgO and eNd are geochemical and isotopical evidences of crustal contamination of these basalts. Our studies show that these basalts have a clear elemental equilibrium with lower and middle crust rocks and that they have been contaminated with them.