Geology, petrography, geochemistry and petrogenesis of intermediate subvolcanic units in the south of Zahedan, Sistan and Baluchestan province, Iran

The study area is located 12 km south of Zahedan city, Sistan and Baluchistan province. Rock units in this area include a series of slightly altered flysch facies units with Eocene age, subvolcanic rocks and basic to intermediate dikes with probably Oligocene-Miocene age. Subvolcanic rocks in the form of stocks and domes intruded into the flysch unit and were cut by intermediate dykes in the later stages. The subvolcanic units of the region have two main compositions diorite-monzodiorite and quartzdiorite-quartzmonzodiorite with porphyry texture. The subvolcanic units of this area are in the range of metalalumin to slightly peralumin and I-type. This is consistent with the evidence such as the widespread presence of hornblende, apatite and sphene in the studied subvolcanic units, which indicates the oxidic conditions and high oxygen fugacity for these rocks at the time of formation. Spider diagrams drawn for trace and rare earth elements show the single origin and the role of fractional crystallization in the formation of these rocks. Based on the spider diagram of rare earth elements, the studied subvolcanic units of LREE elements show a enrichment toward to HREE elements, which is one of the prominent characteristics of calc-alkaline rocks in the subduction zones of the continental margin. These rocks are placed in the tectonomagmic environment diagrams in the adakitic range and in the category of shoshonite and high potassium calc-alkaline rocks, related to subduction environments.