Abstarct: In the east and southeast of Shahrood, there are a numerous basaltic and olivine basalatic lava flows erupted between Oligo-Miocene marl and gypsiferous red marl. During of Oligocene-Miocene periodic time range, these basalts erupted in the sedimentary basin such as lake or shallow depth evaporation environments from feeder dike conduits. In the contact of the basaltic lava flows and marls, especially on the baxse of each lava flow, ouccred extensive peprytization. Peprites are products of reaction between water, lava and sediments. With attention to intensity of the peperitization process, basaltic fragment size varies from a few millimeters to several decimeter. Peprites contain angular basaltic fragments which are vesicular and amygdaloidal texture and structure. They are clear evidence of eruption of basaltic lava flows in the Oligo- Miocene shallow depth sedimentry enviroments and reject previous age (Quaternary) which attributed to these basalts and help us to determine the real stratigraphic position of them.These rocks are microlitic porphyry, glomeroporphyry and hyaloporphyry in textures. Olivine, plagioclase and pyroxene (in olivine basalts) and plagioclase and pyroxene (in basalts) are their major minerals. Evidences of distribution and magma mixing, disequilibrium and child margins have been seen in the studied basalts. Typical evidences of the carried out evolutions are: spherical basaltic globoules, child margins and polystge growthing and sieve texture of plagioclases. Skeletal rounded olivine with corrosion rim along with rounded and pyroxenes ،sieve texture in plagioclases with sieve texture have bin observed. Theire most aboundant minerals are plagioclase and augite and have granular, intergranular, ophitic and subophitic textures.With attention to geochemical data, magma forming of the mentioned basalts has sodic alkaline nature. The alkaline nature and intra-continental plate (Back-arc) environment have been proved for these rocks baxsed on both magmatic series and tectonic setting discerimination diagram They are rich in large ion lithophile elements (LILE) and also indicate enrichment in light rare earth elements (LREEs) and relative depletion in heavy rare earth elements (HREEs). The studied basalts originated from enriched mantle origin (petrogenesis) and show geochemical characteristics of basaltic magma originated from garnet-lherzolitic mantle beneath the back arc extensional crustal environments.