Introduction: A few basic intrusive bodies are located in the northeastern part of Iran within the Gorgan Rashat and the Eastern Alborz Moutain range zones. This plutonism has a relative of the Upper Jurassic to Early Cretaceous ages, and is being introduced for the first time in this paper.Aim: The study and investigation of the intrusive bodies with respect to their origin and state.Materials and Methods: In order to achieve this purpose, the following methods are used: preparation of the necessary number of microscopic thin sections (to study the structure, mineralogy, petrographic characteristics), XRF analysis (in order to obtain the chemical compositions of these rocks), and K-Ar geochronologic method (in order to find the age of the minerals and the entire rock). Firstly, all of the thin sections are studied using a polarized microscope, then selected samples are sent to the lab in order to find and study their chemical compositions. After that, a few samples are analyzed by mass spectrometry to measure their chronologic age.Results: This intrusive body has penetrated the Shemshak formation and from a petrographic point of view, it is a basic type that includes gabbro, gabbro-norite, gabbrodiorite and gabbro-monzonite rocks (listed in order of their importance and abundance). The major minerals present in these rocks are olivine, ortho-clino pyroxenes, and calcic plagioclase. The minor minerals, according to their percentage content, are K-feldspar; which is more abundant in monzo-gabbros than plagioclase, and also apatite, magnetite and amphibole, respectively. Amphibole is more abundant in monzo-gabbroic rocks which have a pegmatitic texture. Quartz, and zircon are also present as minor minerals. The textures are cumulate, and adcumulatic types in gabbro-norites. Also, in other types of rocks, the textures are granular, ophitic, sub-ophitic, intergranular intersertal, and in some cases, are of a pegmatitic type which lack any type of zonation or alteration, as observed. The mechanism and shape of the intrusive studied body is of the laccolith type. The mineralogical composition and crystallization sequence of minerals and the succession of mineralogical fractionation series is comparable to calco-alkaline plutonism. According to the K-Ar method, the chronological age of these intrusive bodies are found to be from 126.4 to 145.6 Ma., Upper Jurassic and Early Cretaceous. These are also related to early Alpian tectonic movements.Conclusion: These intrusive rocks are of the Upper Jurassic and Early Cretaceous, that have Calco-Alkaline magmatism (plutonism), formed along the orogenic belt from Turkey- Ghafghaz (at the west side) to the Band-e-Bayan region in Afghanistan (at the east side). At some regions of this orogenic belt, most geological activities involve plutonism, while volcanic eruptions comprise the minor portion of these activities. According to the location of these plutones and extrusive rocks along this belt, they are formed at volcanoplutonism movements between the Upper Jurassic and Early Cretaceous.