Zagros fold and thrust belt in the Fars province (Iran) I. Control of thickness/rheology of sediments and pre-thrusting tectonics on structural style and shortening

The 300 km long arc of the Fars province is located to the south east of the NW-SE trending and SW vergent orogen of the Zagros Mountains. This region is one of the largest hydrocarbon reserves worldwide, and also as a territory of high quality outcrops. Geological cross-sections of the Zagros belt are usually based on very large scale geological maps (1:1.000.000 or 1:250.000), and on few subsurface data and aim at describing the decoupling relationship between cover and basement rocks and the subduction/collision history of the Arabian – Eurasia plates. In this paper, we present a 253 km long cross-section across the Fars province on the basis of detailed geological maps (1:100.000 scale), field and subsurface data. Our purposes are to: 1) investigate the link between shortening inferred from our original cross-section (from a maximum of 9,1% to a minimum of 4,4%. for different sectors of the belt) and rift-related and flexure-related extensional faults, which in turn, control thickness and lateral facies variations; 2) describe the geometries of folds and thrusts and their relationship with prethrusting normal faults, that were inverted during shortening as transpressional or strike slip faults. Moreover, we present for the first time new field data showing evidences of syn-collisional normal faults likely related to the bending of the Arabian plate in the Fars area.