Geology, petrography and geochemistry of Eocene lavas from the north of Yusuf-Khan-Kandi, north of Lahrud, Ardabil Province

The study area is located in the north of the Yusef -Kandi village, north of Lahrud, Ardabil Province (northwestern Iran). This area comprises portions of the Alborz-Azarbaijan structural zone, which together with the Little Caucasus and the highlands of southeastern Turkey have evolved due to the convergence of the Arabian and Eurasian plates during the Alpine-Himalayan orogeny. The study area includes outcrops of Eocene volcanic and volcano-sedimentary sequences which were deposited in marine to continental environments. The volcanic portion of these sequences consists of volcanoclastic rocks as well as lava flows. A few acidic volcanic rocks and ignimbrite are locally exposed in this area. The petrographic studies show that the Yusef-Khan-Kandi volcanic rocks include picrobasalt, basalt, tephrite, basanite, trachybasalt, basaltic trachyandesite, phenotephrite, tephrophenolite, trachyandesite and trachyte compositions. Phyric texture is common within the volcanic lavas. The majority of the samples show transitional to potassic trends, with only a few samples exhibiting sodic trends. The transitional trend observed in a significant number of the studied samples probably has resulted from the mingling of the sodic and potassic magmas. The Harker binary variation diagrams indicate trends that are consistent with fractional crystallization. The chondrite-normalized REE patterns and primitive mantle-normalized spider diagrams show high LREE/HREE ratios which could be explained by partial melting of an enriched mantle (including asthenospheric) or a metasomatized mantle in collisional to continental arc environments. Most of the studied volcanic rocks plot in the active continental arc or within plate domains. It seems that following the convergence between the Arabian and Eurasian plates in the Late Cretaceous, the northward subducting Neotethyan slab in the Eocene, triggered partial melting of the metasomatized subcontinental lithospheric mantle. Therefore, we suggest that the Yusef-Khan-Kandi Eocene volcanic rocks were erupted in a post-collision extensional environment.