Structural evolution of the western part of Dehsheikh Ultramafic-Mafic complex, Esfandagheh-Faryab ophiolitic mélange belt

The Dehsheikh Ultramafic-Mafic Complex (DUMC), as a portion of the Esfandagheh-Faryab ophiolitic melange belt, accommodates several chromitite ore deposits, but their emplacement and relation to the regional structures remain ambiguous due to structural complexities. The Dehsheikh Ultramafic Massif is composed of harzburgites, dunites, chromitites, pyroxenites, and lherzolites. The chromitite ores, embedded in a dunitic host rock, are concentrated in the central part of the massif in the active Bozorg mine and also abandoned Ajdari and Konar mines. According to the results, the DUMC has experienced three deformational phases of D1-D3. The high-T transtenssional D1 deformation is recognized by injection of the pyroxenitic dykes (Di1), development of the dextral ductile shear zones (Dsz1) and rootless folds (F1) in the dunite-chromitites sequences. These evidences could demonstrate ascending of the Dehsheikh mantle diapir in the upper mantle during the D1 deformation. The D2 dextral transpressional deformation is characterized by formation of the conjugate F1b right-lateral strike slip faults (with reverse component) and F1a thrusts and associated V1 magnesite veins. The D2 structures developed along with emplacement of the DUMC under the prevalent Zagros oblique reverse faulting in the ophiolitic mélange belt. Finally, the D3 was accompanied by conjugate F2a right-lateral strike slip faults (with normal component) and F2b normal faults, associated with development of the V2 magnesite veins under the local transtenssional regime along the Zagros fault. The F1 folds and F1-F2a,b faults structurally controlled deformation and emplacement of the chromitite ore deposits