The Achani interfering folded structure and related linear dyke swarm: a new method to test the Oroclinal buckled arcs; north Qayen, East Iran

Adjacent to the northern border of the Sistan suture zone and the Lut block, north of the Qayen, the Paleocene-Eocene volcano-sedimentary sequence represents an interference pattern of folding. Crescent structures indicate the type 2 of superimposed folding. The axial plan of the first generation of the large-scale folds is generally east-west trended, but along their strike, they are obviously curved to the north and south. A linear dioritic-andesitic dyke swarm, is intruded on this sequence with a radial pattern, and cut the axial plane of the first generation and is affected by the second generation of folding. In order to date this tectono-magmatic event, U-Pb dating is performed on the zircon crystals of these dykes, and an age of ~40 Ma is yielded as the cooling age. The consistency between the dykes’ strikes and the curvature of the first-generation folding axial plane (in response to the second folding event) gave a redial pattern with 30o declination to this dyke swarm. This may indicate the intruding and cooling of the dykes coincide with the second folding generation. Acceptable adaptation of the declination of these dykes to that of the curved axial plane of the first folding episode on the linear regression diagram can be a new method for testing the bends that originally have been linear. Our structural analyses on the Qayen area indicate that Achani structure is a clear example of a larger oroclinal buckling in the region, during the Eocene, coinciding with the formation of the Eastern Iranian Orocline.