ژيـوشيمي و محيط زمين‌ساختي سنگ‌هاي آتشفشاني در كوه تـاوشانا (جنوب‌غرب آستارا)

Geochemistry and Tectonic Setting of Volcanic Rocks in Tavshana Mountain (SW Astara)

The volcanic rocks in Tavshana mountain with Eocene age have exposed in Talesh mountains in west of Guilan province. From petrographical point of view, these rocks mainly include trachyandesites with megaporphiric texture. From geochemical point of view, they are potassic alkaline series and negative anomaly of Nb, Ta, Ti and positive anomaly of K and Pb are evidence of crustal contamination. In tectonic setting diagrams, trachyandesites plot in intra-continental rift basalt, meaning intra-continental extensional belt basalts and or primordial stages of continental rift and shows trend of tholeiite basalts direction to transitional basalt direction, and follow of mantle enrichment and crustal component. The trend of incompatible elements pattern as compared with continental tholeiites and upper Continental crust, show that the primary magma are comparable with continental tholeiits which are contaminated with upper continental crust, and potassic characteristic of the region is not characteristics of the source region. A continental contamination is the main cause for the rise of the amount of the magma potassium and making false potassic and shoshonitic series in region rocks