Petrology and Geochemistry of seyenitic and gabbroic intrusive rocks in the north of Esphordi Phosphate mine (NE Bafq)

The studied area is located at the 30 km northeast of the Bafq city and near the Esphordi phosphate mine. This area composed of Rizu Series rock sequence with Upper Precambrian- Lower Cambrian age. The mentioned sequence has been intruded by some seyenitic and gabbroic intrusions. Petrographical studies indicate that syenites contain hetero- granular, perthite and checkerboard textures and composed of alkali- feldspar (orthoclase), plagioclase, amphibole, pyroxene and biotite. Gabbros contain hetero- granular, and inter- granular textures, and composed of plagioclase, clinopyroxene, amphibole and biotite. Geochemical studies demonstrate that syenites and gabbros have high- K to shoshonitic alkaline nature. Based on the spider diagrams, the two mentioned intrusion have similar trend which can be indicative for their genetic relation. These diagrams indicate enriched LILEs along with negative anomalies of HFSEs. The chondrite normalized REE patterns demonstrate LREEs rich pattern with high ratio of LREE/HREE. The mentioned trends along with positive and negative anomalies of those elements probably are related to lower partial melting degrees of metasomatized mantle along with crustal contamination of this magma. Based on geochemical studies and using the discrimination tectonic setting diagrams, it seems that the studied intrusions were formed at the active continental margins toward post- collisional setting.