Abstarct: The most thickness of Silurian magmatism outcrop in Iran, named Soltan maydan basaltic assemblage, extended in north and northeast of Shahrood, from Nekarman to Khoshyeilagh valley. The study areas are located in Abarsej and Nekarman and in term of structural and geological division, are as part of Eastern Alborz zone. The studied basalts with sharp contact have been erupted on the shale and sandstones of Abarsej Formation (belongs to Late Ordovician) and in the upper contact, covered by the thick polygenetic conglomerates of Padeha Formation (Devonian) composed of particles of Abarsej Formation and mentioned basalts. These basalts observe as numerous lava flows that some of them have prismatic structure, as well as dyke in Abarsej Formation. In the field and petrographical studies, these rocks have homogeneous mineralogy and all of them lie in the realm of basalt. Plagioclase and clinopyroxen are the major minerals of these rocks. The most important minor minerals include olivine, opaque and apatite. Also, effect of alteration on these rocks led to formation of alteration minerals such as epidote, chlorite, calcite, quartz, sericite, sphene and biotite in this rocks. The presence of apatite, titan augite and secondary sphene suggest alkaline nature of these rocks. Porphyry, glomeroporphyry, flow, intergranular, ophitic and subophitic textures are observed important textures of these basalts. Geochemical, petrographical and field studies indicate that these basalts have alkaline nature and formed in an intercontinental setting in Silurian time. Spider diagrams indicate enrichment in LREE, MREE, LILE and depletion in HREE in these rocks, that indicating low degree partial melting and presence of garnet in the source of magma. Also, lack of negative anomaly of HFSE is the indicator of intercontinental alkaline magmatism and uncontamination magma with continental lithosphere. Enrichment close to 1 in OIB normalized spider diagram and high HFSE/LREE ratio in these basalts indicates an asthenospheric source for their magma. baxsed on, petrogenetic and geochemical studies, the alkaline magma of these basalts has been formed from 14-16% partial melting of a garnet peridotitic rising enriched mantle plume in 100-110 km depth and erupted in a continental-shallow sea environment. This environment, corresponds to rifting of northern side of Gondowana in Ordovician-Silurian that led to formation of Palaeotethys ocean in the recent place of Alborz mountains.