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Forward propagation of the Zagros Simply Folded Belt constrained from magnetostratigraphy of growth strata

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Abstract

The temporal evolution of the Zagros Simply Folded Belt is constrained by a magnetostratigraphic sequence containing a progressive unconformity on the southern limb of the Kuh-e Ghol Ghol anticline, in the Central Fars. The investigated ~1400 m thick sequence exposes a regressive megacycle containing, from bottom to top, open and shallow marine marls and sandy limestones, fine- to coarse-grained fluvial deposits and alluvial conglomerates. Correlating 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 the accumulation rate from ~15 cm/ka to ~40 cm/ka, as measured on lithified sediments. Alluvial river deposits first occurred at ~3.2 Ma. The Kuh-e Ghol Ghol anticline began to grow at ~3.8 Ma, witnessing fastest limb rotation rates of 40°/Ma at ~3.3 Ma. Reporting magnetostratigraphic sections and ages of growth strata on a map of NE Fars reveal an ~1 cm/a, southwestward migration rate of the deformation front during the middle and late Miocene.

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