Tectonic History and Present-Day Deformation in the Zagros Fold-Thrust Belt

University dissertation from Uppsala : Acta Universitatis Upsaliensis

Abstract: This thesis uses various approaches such as observation of satellite images, field investigations, analogue modeling and GPS measurements to constrain deformation of the basement and sedimentary cover of the Zagros fold-thrust belt in time and space.Focal mechanism solutions of most earthquakes indicate that deformation in the Zagros basement is due to shortening and thickening through numerous thrust faults. However, observations of strike-slip faulting recognized on satellite images imply that N-S trending faults in the Zagros, inherited from Pan-African basement, rotated about vertical axes to accommodate the convergence between Arabia and central Iran.Field studies suggest that southwestward advance of the Zagros front has been recorded by syn-sedimentary structures. These structures indicate that deformation started as early as end Eocene in the northeast of the Simply Folded Zone and propagated progressively to the southwest. The deformation front drove the foreland basin to its present position along the Persian Gulf and Mesopotamia. Scaled analogue models suggest that the seismicity due to orogenic shortening depends largely on the friction between the cover and its basement. Models show that fold-thrust belts with low tapers shortened above low friction ductile decollements involve several long-lived thrust faults generating low to moderate earthquakes over wide areas at the same time. By contrast, earthquakes with larger magnitudes are expected to occur along a few short-lived thrust ramps in fold-thrust belts with larger tapers shortened above high-friction decollments.GPS-derived velocities across and along the Zagros suggest that only about one third (10 ± 3 mm/yr) of the current convergence between Arabia and Eurasia is accommodated within the Zagros by thickening to the east of the Kazerun Fault and thickening and lateral movement to the west. The remaining (21 ± 3 mm/yr) is transferred beyond the Zagros suture to central Iran and the northern Iranian mountains.

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