Geometries and Kinematics of Thrust Faults in the Zagros Fold and Thrust Belt and Implications for Hydrocarbon Prospectivity

Blanc, Eric J-P.¹, Mark B. Allen², James Jackson³, Richard Walker⁴, Christopher Wibberley⁵, Morteza Talebian⁶, Hossein Hassani⁷, James P. Howard⁸ (1) CASP, Department of Earth Sciences, University of Cambridge, Cambridge, United Kingdom (2) University of Durham, Durham, United Kingdom (3) Bullard Laboratories, Universityof Cambridge, Cambridge, England (4) Department of Earth Sciences, University of Oxford, Oxford, United Kingdom (5) Université Nice-Sophia Antipolis, Valbonne, France .(6) Geological Survey of Iran, Tehran, Iran (7) Amirkabir University of Technology, Tehran, Iran (8) CASP, University of Cambridge, Cambridge, United Kingdom

The Zagros Fold and Thrust Belt (FTB) is a world-class hydrocarbon province and an active part of the Eurasia-Arabia collision zone. There are still many uncertainties concern­ing the hydrocarbon potential of unexplored deeper structures beneath the Zagros surface folds. Field observations point to a highly heterogeneous mechanical stratigraphy with sev­eral well-defined detachment levels and structures typical of thin-skinned deformation. Although seismically active thrust faults are restricted to parts of the Zagros with elevations of less than 1 km, the occurrence of large earthquakes at depths greater than 12 km and up to ~20 km implies that the Zagros FTB is, at least in part, undergoing thick-skinned defor­mation. There are still major uncertainties about the exact shape and kinematics of the faults underlying the Zagros folds. On one hand, seismology, indicates that seismically active thrusts are steep (30-55°) and, by analogy with other case studies, probably fairly constant­ly dipping through the upper and middle crust down to a depth of ~20 km. On the other hand, geological observations and serial cross-section balancing suggest that dips and dis­placements have to change along faults to accommodate the shortening at various levels of the crust. This is a problem not only for the deeper part of the crust but also for its shallow­er part, making it directly relevant to the oil industry. Several possible models and their respective bearings on potential deep hydrocarbon plays geometries are reviewed here.