Influence of a transverse basement fault on along-strike variations in the geometry of an inverted normal fault: Case study of the Mosha Fault, Central Alborz Range, Iran

Inverted normal faults show variations in structural geometry from footwall shortcut thrusts to hanging-wall break-back thrusts. In the present study, we evaluated along-strike variations in the geometry of the Mosha Fault, Central Alborz Range, Iran. Detailed structural mapping within the Taleqan Mountains revealed that the Mosha Fault in the eastern part of the study area is associated with a large, basement-cored hanging-wall anticline thrust over Tertiary rocks that occur as a syncline or cut by footwall shortcut thrusts. In the western part of the study area, however, the hanging wall consists of break-back thrust sheets of Paleozoic–Mesozoic rocks. These thrust sheets occur as a duplex system and have allochthonous masses gravitationally emplaced in the foothills of the Taleqan Mountains. Curved fold axial traces and scattered intrusive bodies are observed in the Valian Valley area, where the Mosha Fault is displaced across a transverse basement fault. This basement fault controlled along-strike variations in the geometry of the Mosha Fault during its evolution from a basin-bounding fault to an inverted normal fault. Inversion of the fault in the eastern part of the study area, where the fault is relatively steep, involved basement rocks; in the western part of the study area, where the fault is relatively shallowly dipping, deformation in the hanging wall is accommodated by thin-skinned break-back thrust sheets.