Structures of the Zagros fold-thrust belt in Iran

The Zagros fold-thrust belt in Iran forms the external part of the Zagros active orogenic wedge. It includes a sequence of heterogeneous latest Neoproterozoic–Phanerozoic sedimentary cover strata, ∼7 to 12 km thick and composed of alternating incompetent and competent layers, overlying Precambrian crystalline basement with a complex pre-Zagros structural fabric. Balancing structures of the cover statigraphic units in the Zagros fold-thrust belt requires in-sequence and out-of-sequence involvement of the Precambrian basement in the deformation. Six detailed balanced and retrodeformable cross-sections, which are constructed based on geological and geophysical data across various sectors of the belt, show fault-bend and fault-propagation folds interpreted to have formed by slip on their subjacent thrusts. Out-of-sequence, basement-rooted thrusts, as the interpretations in the constructed cross-sections suggest, have breached the cover/basement interface and, using incompetent cover strata for propagation, cut across the cover structures and have created associated new folds superimposed upon the pre-existing structures. This style of deformation, which has resulted in structural complexity of the belt, characterizes a ∼200 to 300 km-wide zone of distributed, partly synchronous, deformation with along-strike and across-strike variations. It also implies that the Zagros fold-thrust belt, as the external part of the orogenic wedge, is still in its subcritical condition with internal deformation to achieve a critical taper. In creating structural complexity, in addition to out-of-sequence thrusting, mechanically weak layers (evaporites and mudstones) of the cover strata have played a significant role by providing several detachment horizons. Shortening estimates across the belt are variable; based on the constructed cross-sections and their restorations, minimum shortening estimates range from 16 percent to 30 percent in different sectors of the belt.

[1]  A. Ravaglia,et al.  Mechanical stratigraphy as a factor controlling the development of a sandbox transfer zone: a three-dimensional analysis , 2004 .

[2]  H. Mcquillan.  The role of basement tectonics in the control of sedimentary facies, structural patterns and salt plug emplacements in the Zagros fold belt of southwest Iran , 1991 .

[3]  J. V. Harrison.  The Geology of some Salt-Plugs in Laristan, Southern Persia , 1930, Quarterly Journal of the Geological Society of London.

[4]  J. Dixon,et al.  Centrifuge modelling of the propagation of thrust faults , 1992 .

[5]  J. Epard,et al.  Excess Area and Depth to Detachment , 1993 .

[6]  H. Koyi,et al.  Experimental and field study of the effects of lithological contrasts on thrust‐related deformation , 2003 .

[7]  Andrea Walpersdorf,et al.  The present‐day deformation of the central Zagros from GPS measurements , 2002 .

[8]  The crustal and upper‐mantle structure of the interior Arabian platform , 1999 .

[9]  J. Cosgrove,et al.  Structural framework of the Zagros Fold-Thrust Belt, Iran , 2004 .

[10]  J. Makris,et al.  The Gravity Field and Crustal Structure of Iran , 1984 .

[11]  M. Tatar,et al.  Tectonics of the Central Zagros (Iran) deduced from microearthquake seismicity , 2004 .

[12]  W. Ryan,et al.  Plate Tectonics and the Evolution of the Alpine System , 1973 .

[13]  I. F. Stewart,et al.  Magnetically inferred basement structure in central Saudi Arabia , 1995 .

[14]  A. Nowroozi,et al.  A reply to discussion on “Focal mechanism of earthquakes in Persia, Turkey, West Pakistan, and Afghanistan and plate tectonics of the Middle East” , 1973, Bulletin of the Seismological Society of America.

[15]  M. N. Bushara.  Subsurface Structure of the Eastern Edge of the Zagros Basin as Inferred from Gravity and Satellite Data , 1995 .

[16]  P. Fermor.  Aspects of the three-dimensional structure of the Alberta Foothills and Front Ranges , 1999 .

[17]  Daniel M. Davis,et al.  GREAT THRUST EARTHQUAKES AND ASEISMIC SLIP ALONG THE PLATE BOUNDARY OF THE MAKRAN SUBDUCTION ZONE , 1992 .

[18]  J. Jackson,et al.  A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran , 2004 .

[19]  F. A. Dahlen,et al.  Noncohesive critical Coulomb wedges: An exact solution , 1984 .

[20]  J. Pamić,et al.  Alpine magmatic and metamorphic processes and plate tectonics in the Zagros Range, Iran , 1979 .

[21]  S. E. Boyer.  Geometric evidence for synchronous thrusting in the southern Alberta and northwest Montana thrust belts , 1992 .

[22]  J. Suppe,et al.  Geometry and kinematics of fault-propagation folding , 1990 .

[23]  K. Priestley,et al.  A re‐assessment of focal depth distributions in southern Iran, the Tien Shan and northern India: do earthquakes really occur in the continental mantle? , 2000 .

[24]  A. Şengör,et al.  A new model for the late Palaeozoic—Mesozoic tectonic evolution of Iran and implications for Oman , 1990, Geological Society, London, Special Publications.

[25]  J. Suppe,et al.  Mechanics of fold-and-thrust belts and accretionary wedges , 1983 .

[26]  M. Alavi.  Tectonostratigraphic evolution of the Zagrosides of Iran , 1980 .

[27]  R. Stoneley,et al.  Petroleum in the Zagros Basin: A Late Tertiary Foreland Basin Overprinted onto the Outer Edge of a Vast Hydrocarbon-Rich Paleozoic-Mesozoic Passive-Margin Shelf: Chapter 11 , 1992 .

[28]  H. S. Edgell.  Proterozoic salt basins of the Persian Gulf area and their role in hydrocarbon generation , 1991 .

[29]  R. J. Murris.  Middle East: Stratigraphic Evolution and Oil Habitat , 1980 .

[30]  C. Talbot,et al.  The past of a future syntaxis across the Zagros , 1996, Geological Society, London, Special Publications.

[31]  J. Suppe,et al.  Balanced Geological Cross-Sections: An Essential Technique in Geological Research and Exploration , 1991 .

[32]  Sean D. Willett,et al.  Orogeny and orography: The effects of erosion on the structure of mountain belts , 1999 .

[33]  G. Stockmal.  Modeling of large-scale accretionary wedge deformation , 1983 .

[34]  J. Suppe,et al.  Mechanics of fold‐and‐thrust belts and accretionary wedges: Cohesive Coulomb Theory , 1984 .

[35]  Richard G. Gordon,et al.  Current plate motions , 1990 .

[36]  H. Koyi,et al.  Tectono-Sedimentary framework of the Gachsaran Formation in the Zagros foreland basin , 2004 .

[37]  J. Stocklin.  Structural History and Tectonics of Iran: A Review , 1968 .

[38]  R. Stoneley,et al.  Subsidence history of the Middle East Zagros Basin, Permian to Recent , 1982, Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences.

[39]  D. Snyder,et al.  Deep crustal structure and flexure of the Arabian Plate Beneath the Zagros collisional mountain belt as inferred from gravity observations , 1986 .

[40]  M. Alavi,et al.  The Triassic and associated rocks of the Nakhlak and Aghdarband areas in central and northeastern Iran as remnants of the southern Turanian active continental margin , 1997 .

[41]  F. A. Dahlen,et al.  CRITICAL TAPER MODEL OF FOLD-AND-THRUST BELTS AND ACCRETIONARY WEDGES , 1990 .

[42]  A. Alsharhan,et al.  Sedimentary basins and petroleum geology of the Middle East , 1997 .

[43]  Compressional structures in a multilayered mechanical stratigraphy: Insights from sandbox modeling with three-dimensional variations in basal geometry and friction , 2001 .

[44]  Mohsen Ghafory-Ashtiany,et al.  Seismological constraints on the crustal structure beneath the Zagros Mountain belt (Iran) , 2003 .

[45]  S. J. Haynes,et al.  Evolution of the Zagros Suture Zone, Southern Iran , 1974 .

[46]  J. Suppe,et al.  Geometry and kinematics of fault-bend folding , 1983 .

[47]  A. Gansser.  The enigma of the Persian salt dome inclusions , 1992 .

[48]  P. Cobbold,et al.  Some experiments on interacting sedimentation and deformation above salt horizons , 1989 .

[49]  G. Mitra.  Evolution of salients in a fold- and-thrust belt: the effects of sedimentary basin geometry, strain distribution and critical taper , 1997 .

[50]  Robert D. Tucker,et al.  The Saghand Region, Central Iran: U-Pb geochronology, petrogenesis and implications for Gondwana Tectonics , 2003 .

[51]  M. Berberian,et al.  Late Cretaceous and early Miocene Andean-type plutonic activity in northern Makran and Central Iran , 1982, Journal of the Geological Society.

[52]  W. Walter,et al.  Lithospheric structure of the Arabian Shield and Platform from complete regional waveform modelling and surface wave group velocities , 1999 .

[53]  D. Karig,et al.  Makran of Iran and Pakistan as an active arc system , 1977 .

[54]  D. McKenzie,et al.  Active thrusting and the evolution of the Zagros fold belt , 1981, Geological Society, London, Special Publications.

[55]  N. McQuarrie,et al.  Crustal scale geometry of the Zagros fold–thrust belt, Iran , 2004 .

[56]  K. McClay,et al.  Physical models of thrust wedges , 1992 .

[57]  M. Cooke,et al.  The effect of non-parallel thrust fault interaction on fold patterns , 2004 .

[58]  S. Sherkati,et al.  Variation of structural style and basin evolution in the central Zagros (Izeh zone and Dezful Embayment), Iran , 2004 .

[59]  Hemin Koyi,et al.  THE SIGNIFICANCE OF STRIKE‐SLIP FAULTING IN THE BASEMENT OF THE ZAGROS FOLD AND THRUST BELT , 2001 .

[60]  D. Stoeser,et al.  Pan-African microplate accretion of the Arabian Shield , 1985 .

[61]  S. Stewart.  Geometry of thin‐skinned tectonic systems in relation to detachment layer thickness in sedimentary basins , 1999 .

[62]  Assad Iranpanah.  Thematic mapping of basement-related cross-strike structural discontinuities and their relationship to potential oil-bearing structures , 1989 .

[63]  J. Brun,et al.  Deformation of brittle-ductile thrust wedges in experiments and nature , 2003 .

[64]  James Ni,et al.  Seismotectonics of the Zagros continental collision zone and a comparison with the Himalayas , 1986 .

[65]  S. Marshak,et al.  Origin of the Uinta recess, Sevier fold–thrust belt, Utah: influence of basin architecture on fold–thrust belt geometry , 1999 .

[66]  K. Kadinsky-Cade,et al.  Seismotectonics of southern Iran: The Oman Line , 1982 .

[67]  K. Schmidt,et al.  Mesozoic—Cenozoic Geological Events in Central-East-Iran and their Relation to Palaeomagnetic Results , 1984 .

[68]  P. Kent.  Recent Studies of South Persian Salt Plugs , 1958 .

[69]  S. Mitra.  Fault-propagation folds: Geometry, kinematic evolution, and hydrocarbon traps , 1990 .

[70]  J. Jackson,et al.  The depth of seismicity in the Kermanshah region of the Zagros Mountains (Iran) , 1978 .

[71]  R. J. Lillie,et al.  Balanced and retrodeformed geological cross-section from the frontal Sulaiman Lobe, Pakistan: Duplex development in thick strata along the western margin of the Indian Plate , 1992 .

[72]  C. Talbot,et al.  Salt extrusion at Kuh-e-Jahani, Iran, from June 1994 to November 1997 , 2000, Geological Society, London, Special Publications.

[73]  K. Priestley,et al.  Earthquakes on the Kazerun Line in the Zagros Mountains of Iran: strike‐slip faulting within a fold‐and‐thrust belt , 1993 .

[74]  Frederic Masson,et al.  Present‐day crustal deformation and plate kinematics in the Middle East constrained by GPS measurements in Iran and northern Oman , 2004 .

[75]  W. A. Thomas.  Evolution of Appalachian-Ouachita salients and recesses from reentrants and promontories in the continental margin , 1977 .

[76]  K. McClay,et al.  Influence of syntectonic sedimentation on thrust wedges in analogue models , 1995 .

[77]  N. Kukowski,et al.  Structure of the Makran subduction zone from wide-angle and reflection seismic data , 2000 .

[78]  T. Engelder,et al.  The role of salt in fold-and-thrust belts , 1985 .

[79]  D. Rankin,et al.  Appalachian salients and recesses: Late Precambrian continental breakup and the opening of the Iapetus Ocean , 1976 .

[80]  P. E. Kent,et al.  THE EMERGENT HORMUZ SALT PLUGS OF SOUTHERN IRAN , 1979 .

[81]  S. Erickson.  Influence of mechanical stratigraphy on folding vs faulting , 1996 .

[82]  R. White,et al.  Tectonics of the western Gulf of Oman , 1979 .

[83]  C. Vita-Finzi,et al.  Neotectonics at the Arabian plate margins , 2001 .

[84]  A. Bahroudi,et al.  THE CONFIGURATION OF THE BASEMENT BENEATH THE ZAGROS BASIN , 2003 .

[85]  M. G. Ionides,et al.  The Geographical History of the Mesopotamian Plains , 1952 .

[86]  S. Colman-Sadd.  Fold Development in Zagros Simply Folded Belt, Southwest Iran , 1978 .

[87]  John W. Cosgrove,et al.  The interplay of faulting and folding during the evolution of the Zagros deformation belt , 1999, Geological Society, London, Special Publications.

[88]  N. L. Falcon.  Problems of the relationship between surface structure and deep displacements illustrated by the Zagros Range , 1969, Geological Society, London, Special Publications.

[89]  Stephen Marshak,et al.  Generation of curved fold-thrust belts: Insight from simple physical and analytical models , 1992 .

[90]  R. J. Lillie,et al.  Structural Development within the Himalayan Foreland Fold-And-Thrust Belt of Pakistan , 1987 .

[91]  H. Wensink.  Paleomagnetism of red beds of Early Devonian age from Central Iran , 1983 .

[92]  E. Shabanian,et al.  Late Cenozoic partitioning of oblique plate convergence in the Zagros fold‐and‐thrust belt (Iran) , 2006 .

[93]  J. Platt.  Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks , 1986 .

[94]  H. Koyi,et al.  Modeling of thrust fronts above ductile and frictional detachments: Application to structures in the Salt Range and Potwar Plateau, Pakistan , 2000 .

[95]  J. Suppe,et al.  A Forward Modeling Strategy for Balancing Cross Sections (1) , 1990 .

[96]  M. Alavi,et al.  Stratigraphy and structures of the Nahavand region in western Iran, and their implications for the Zagros tectonics , 1994, Geological Magazine.

[97]  William M. Chapple,et al.  Mechanics of thin-skinned fold-and-thrust belts , 1978 .

[98]  E. Costa,et al.  Experimental insights on the geometry and kinematics of fold-and-thrust belts above weak, viscous evaporitic décollement , 2002 .

[99]  J. Cosgrove,et al.  A comparison of the geometry, spatial organization and fracture patterns associated with forced folds and buckle folds , 1999, Geological Society, London, Special Publications.

[100]  George Bird.  Thermal and mechanical evolution of continental convergence zones : Zagros and Himalayas. , 1976 .

[101]  Philippe Fullsack,et al.  Erosional control of active compressional orogens , 1992 .

[102]  C. D. A. Dahlstrom.  Balanced cross sections , 1969 .

[103]  M. Takin.  Iranian Geology and Continental Drift in the Middle East , 1972, Nature.

[104]  G. Schubert,et al.  Models of post‐Miocene deformation of the Arabian Plate , 1987 .

[105]  M. Badri.  Crustal structure of central Saudi Arabia determined from seismic refraction profiling , 1991 .

[106]  N. B. Woodward,et al.  Structural lithic units in external orogenic zones , 1989 .

[107]  Timothy H. Dixon,et al.  REVEL: A model for Recent plate velocities from space geodesy , 2002 .