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Geometry and kinematics of the SE Zagros Mountains (Iran) : structural geology and geophysical modelling in a young collisional fold-thrust belt

Abstract : This thesis focuses on the structure and kinematics of the south-eastern Zagros Mountains (Iran) and the transitional structures with the adjacent Makran accretionary prism, known as the Bandar Abbas syntaxis. The structural framework of this complex region, as evidenced by detailed field-based mapping and balanced cross-sections through some key structures, is strongly controlled by changing mechanical stratigraphy from one side to the other of the syntaxis. Large folds detaching over a thick 8-9 km deep salt layer on the western side suddenly give way to narrow folds controlled by frictional slip along a 6-km deep horizon in the east. This is explained by changing paleogeographic conditions from one side to the other of the syntaxis ultimately related to inherited (Precambrian) structural features of the eastern Arabian margin. Restoration of the first complete balanced cross-section through the south-eastern Zagros fold-thrust belt shows that the external part of the orogen (a) underwent two main phases of deformation, i.e. a Mio-Pliocene thin-skinned phase of deformation followed and partly overprinted by a Pliocene to recent thick-skinned phase currently underlined by intense mid-crustal seismic activity throughout Zagros, and (b) absorbed at least 45 km of shortening since middle Miocene times. The presence of an exceptionally thick layer of salt at the base of the cover allowed the development of huge detachment anticlines. Field examples from our study area and seismic profiles from Central Zagros allow us to discuss the still poorly understood kinematics of these folds as well as examine the various factors controlling the style of folding, essentially salt mobility, multiple decollement levels and late basement faulting. Finally, geophysical modelling of the deep lithospheric structure of Zagros brings new insight on the fundamental factors controlling the recent orogenic dynamics. In particular, a previously undocumented thinning of the lithosphere beneath Zagros could be attributed to recent slab break-off. It is argued that such a major dynamic event could have modified the orogenic wedge taper and triggered the previously discussed switch from thin-skinned to thick-skinned tectonics.
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https://tel.archives-ouvertes.fr/tel-00007533
Contributor : Matteo Molinaro <>
Submitted on : Friday, November 26, 2004 - 4:12:18 PM
Last modification on : Wednesday, December 9, 2020 - 3:04:57 PM
Long-term archiving on: : Friday, April 2, 2010 - 9:09:09 PM

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  • HAL Id : tel-00007533, version 1

Citation

Matteo Molinaro. Geometry and kinematics of the SE Zagros Mountains (Iran) : structural geology and geophysical modelling in a young collisional fold-thrust belt. Applied geology. Université Paris Sud - Paris XI, 2004. English. ⟨tel-00007533⟩

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