Petrogenesis of Southern Amlash Alkaline Rocks in the South Caspian Sea, North of Iran

South Amlash alkaline rocks, located in south of Caspian Sea, occur like small and discrete bodies within the Cretaceous igneous rock association which is a small part of Gorgan-Rasht tectonic zone. These rocks crop out as large-volume pillow lavas and homogeneous fine- to coarse- grained gabbros and are essentially composed of Clinopyroxene (augite), plagioclase and relatively abundant small apatite needles. Geochemical data clearly identifies an enrichment of LREE and positive anomalies of Nb and Ti suggesting an intra-plate ocean island (OIB) tectonic setting. Considering the LREE/HREE ratio and some of other incompatible element contents, it seems that the alkaline rocks are probably derived from a garnet lehrzolitic mantle.