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Rates and processes of active folding in the central Zagros - Iran

Abstract : The Zagros fold belt (Iran) results from active collision of the Arabian plate with central Iran. Although the geology and the structure of the Zagros have been studied extensively, the distribution of active deformation and seismotectonic behaviour across the belt remain poorly constrained. We have mapped deformed fluvial terraces along the Dalaki and Mand rivers in the central Zagros, as well as marine terraces along the Persian Gulf, in order to unravel the spatial pattern of vertical displacements and to analyze active deformation and its implications for seismicity. Using appropriate fold models based on structural data allows to efficiently estimate horizontal shortening from tectonic uplift recorded by marine and fluvial terraces. Obtaining well-constrained rates of deformation depends on reliably dating deformed geomorphic markers; by combining different dating techniques (cosmogenic isotopes Be-10 and Cl-36, and C-14 dating of organic material) and making sensible correlations to the regional climate and sea-level history, we propose an internally consistent set of ages, which allow the first geomorphic estimates of shortening rates absorbed by individual structures in the central Zagros. This approach enables us to consider rates of shortening absorbed by various structures in the central Zagros on Late Pleistocene timescales (10,000 to 1,000,000 years). Our results show that shortening on these timescales is concentrated in the frontal part of the belt, consistent with recent GPS data. Three or four frontal structures appear to absorb practically all of the active shortening across the Zagros, suggesting a normal forward-propagating deformation sequence in a thin-skinned tectonic regime during at least the Late Pleistocene, with south-westward migration of the front of the wedge and a predictable evolution of fold structure and kinematics. In addition, comparing the rate and direction of shortening across individual structures with the distribution of seismicity suggests that the sedimentary cover of the frontal Zagros is decoupled from the basement, most probably at the level of the Hormuz Salt. This weak basal detachment level, together with several intermediate weak décollement levels, appears to be responsible for the overwhelmingly aseismic deformation of the Zagros sedimentary cover.
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https://tel.archives-ouvertes.fr/tel-00161998
Contributor : Peter van der Beek <>
Submitted on : Thursday, July 12, 2007 - 10:34:18 AM
Last modification on : Thursday, November 19, 2020 - 3:54:26 PM
Long-term archiving on: : Thursday, April 8, 2010 - 8:09:11 PM

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  • HAL Id : tel-00161998, version 1

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Behnam Oveisi. Rates and processes of active folding in the central Zagros - Iran. Tectonics. Université Joseph-Fourier - Grenoble I, 2007. English. ⟨tel-00161998⟩

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