Informations et ressources scientifiques
sur le développement des zones arides et semi-arides

Titre : Dynamic evolution of thin-skinned fold-and-thrust belts - field study, magnetostratigraphy and numerical modelling applied to the Zagros and Makran mountains (Iran)

Auteur : Ruh Jona Bruno

Etablissement de soutenance : Swiss Federal Institute of Technology (Zurich) ETHZ

Grade : Doctor of Sciences 2013

Résumé partel
Thin-skinned fold-and-thrust belts related to convergent tectonics develop by scraping off a rock sequence along a weaker basal décollement, which is often formed by water saturated shale layers or low-viscosity salt horizons. Although thin-skinned fold-and thrust belts are among the best and most investigated geological features on earth, there are many aspects that need further examination. The interplay between surface processes and the dynamic structural evolution is tested by magnetostratigraphy of progressive unconformities in the onshore Makran accretionary wedge and the Zagros foreland fold-and-thrust belt. The impact of décollement and wedge rheology on the long-term evolution of thin-skinned fold-and-thrust belts is investigated with numerical modelling and applied to the Makran and the Zagros. Comparison of numerical results to analytical solutions has been conducted.

Progressive unconformities are predestined to link sedimentary and deformation pro cesses in tectonically active settings. In the onshore Makran accretionary wedge, growth strata are found in large-wavelength, small-amplitude concentric synclines. The mor phology of the growth strata indicates an underfilled basin where fold amplification was faster than sedimentation, forming typical sedimentary offlap structures. Magne tostratigraphy did not reveal any characteristic remanent magnetization. > 50% of the natural remanent magnetization was removed by step-wise thermal heating already above 200°C.

The temporal evolution of deformation in the Zagros Simply Folded Belt is constrained by a magnetostratigraphic sequence containing a progressive unconformity in the Central Fars. The correlation of the magnetostratigraphic section with the geomagnetic polarity time scale constrains the transition from marine to fluvial sediment deposition at ∼ 6 Ma. This transition was accompanied by a change in accumulation rate from ∼ 15 cm/ka to ∼ 40 cm/ka. Alluvial river deposits first occurred at 3.2 − 3.1 Ma. In the Central Fars folding was initiated at 3.7 − 3.5 Ma. Comparing magnetostratigraphic sections and ages of growth strata in Central and NE Fars indicates a ∼ 1 cm/a migration rate of the deformation front towards the SW during the Middle and Late Miocene.

Présentation

Version intégrale (105 Mb)