Petrology and Presentation: A Seven-Stage Model forGeodynamic Evolution of the Northeast Region of Birjand,East of Northern Lut, Eastern Iran

Abstract

The northeast region of Birjand is located in Lut structural and geological province. In this area we can distinguish two separate volcanic rock groups: intermediate to acidic volcanic rocks, including dacite, andesite, rhyolite and trachyandesite; and basic rocks, including basaltic andesite, mugearite and basalt. In this region, intermediate to acidic rocks, which belong to the Eocene-Miocene period according to dating results, are the main formation, and we can see the second, younger (evidently Pliocene) volcanic rock group as outcrops with a northwest-southeast trend in the background of the intermediate to acidic volcanic rocks. Geochemical studies show the differences between these two distinctive groups clearly, and reveal that intermediate to acidic rocks belong to active continental margin calc-alkaline rocks. Studies also show the related mantle magma has been influenced by subducted lithospheric slab and metasomatized by crustal materials. The second volcanic rock group belongs to within-plate alkaline rocks. The linear successions and the arrangement of the basic volcanic rocks' outcrop in a northwest–southeast trend is in relation to the right lateral fault zones that have branched out of the Nehbandan fault system. As a result of the extensional regime development, and the high depth of these faults, alkaline magma could have formed and ascended to the surface. Considering with accepted ideas concerning eastern Iran geodynamic evolution and our new data, we have tried to complete the previous findings and present a seven-stage model for geological evolution of eastern Iran.