Petrology and geochemistry of the basic rocks at the Shemshak Formation in the Zinabad area, NW of Tabriz

The study area is located near the Zeinabad village, NW Tabriz. Precambrian to Cretaceous sedimentary units form the dominant outcropping rocks in this area. The investigated basic rocks including lava and diabasic dikes are intruded within the Late Triassic-Early Jurassic sandstone, conglomerate and shales of the Shemshak Formation. The basic rocks are extremely alterated and have abundant vesicles filled by secondary minerals of chlorite, calcite, Zeolite and opaque phases. Petrographic studies of the basic rocks reveal that the plagioclase forms the main constituent mineral and Fe-Mg bearing minerals (most probably hornblende) are completely altered to the calcite, chlorite, epidote and opaqe phases. The most significant textures are porphyry, glomeroporphyry, amygdaloid, sieve and sub-ophitic. Geochemically, the basic rocks are basalts with alkaline signitures. On the basis of variation diagrams, the compositions of analysed rocks are rich of U, Th and LILE (such as Ba, Rb). Positive anaomaly of Pb in these diagrams can be interpreted by the continental crust distribution and/or mantle wedge metasomatism related to the released fluids from subducted oceanic crust. Considering the REE diagrams, the rocks are rich in the LREE but poor in the HREE. High La can be related to Yb contents and can be interpreted to reveal their formations from the garnet bearing mantle sources. Tectonic setting of Zinabad basic rocks is determined as within plate setting. They form in relation with the extensional phases after continental collision during Cimmerian Orogeny in the Azarbaijan continental crust, NW Iran.