Abstract
Abstract The integration of biostratigraphy, strontium isotope stratigraphy, and magnetostratigraphy allowed for the precise dating of the >3.0-km-thick marine to non-marine foreland sedimentary succession within the Dowlatabad growth syncline along the Frontal Fars arc in the Zagros Fold Belt that extends from eastern Turkey to southern Iran. This area was the missing link to complete the dating of syntectonic deposits in the Fars arc and quantify the migration of sedimentary belts as well as the propagation of folding across the entire Mesopotamian foreland basin. Both are essential for defining the interplay of basin evolution and sequence of folding. Deposition of the foreland marine marls in the Mishan Formation started at ca. 11.5 Ma. The transition to a non-marine basin infill occurred at 4.9 Ma by the progradation of thick fluvial deposits of the Aghajari Formation with a fast accumulation rate of 63 cm/k.y. The beginning of growth strata deposition and thus the onset of folding in the Dowlatabad syncline is dated at 4.65 Ma. The first appearance of carbonate conglomerates sourced from the Guri limestone at 2.8 Ma marked the progressive dismantling of the nearby growing anticlines. The tectonic deformation in the front of the Fars arc was active for at least 2.85 m.y. and ceased at 1.8 Ma before the deposition of the discordant and slightly folded Bakhtyari conglomerates characterized by a clast composition derived from the Zagros hinterland. The compilation of magnetostratigraphic ages reveals that both the migration of the Aghajari-Bakhtyari sedimentary belts and the propagation of the folding front was in-sequence toward the foreland at a rate close to 20 mm/yr in the Fars arc and 15 mm/yr in the Lurestan arc, in the last 20 m.y. These high rates of folding propagation are about one order of magnitude larger than age equivalent shortening rates (∼4 mm/yr in Fars arc and ∼2 mm/yr in Lurestan arc) and thus imply an efficient detachment level at the base of the deformed Arabian sedimentary cover. Numerical experiments on both the cover and basement sequences are designed to test the influence of inherited basement structures on the deformation propagation within the cover sequence, providing clues on the partly coeval in-sequence deformation of the Zagros Simply Folded Belt and the local out-of-sequence Mountain Frontal Fault system as illustrated by regional and local geology.
Highlights
The Zagros Mountains form a large segment of the Alpine–Himalayan orogenic system between Arabia and Eurasia evolving during a long-lasting and multi-episodic orogeny by a combination of thin-skinned folding and basement-involved thrusting (Fig. 1)
Neo-Tethys occurred as a hard collision phase characterized by increasing crustal thickening since the early Miocene during which deformation propagated towards the craton interior to build the Zagros Mountains and their coupled foreland basin (Hessami et al, 2001; Mouthereau et al, 2007, 2012; Ruh et al, 2014; Pirouz et al, 2015; Vergés et al, 2019; Etemad-Saeed et al, 2020)
During the Arabia-Eurasia collision, the tectonic evolution of the Zagros Fold Belt was shaped by the interplay of thin-skinned detachment folding of the Phanerozoic sedimentary cover
Summary
The Zagros Mountains form a large segment of the Alpine–Himalayan orogenic system between Arabia and Eurasia evolving during a long-lasting and multi-episodic orogeny by a combination of thin-skinned folding and basement-involved thrusting (Fig. 1). During the Arabia-Eurasia collision, the tectonic evolution of the Zagros Fold Belt was shaped by the interplay of thin-skinned detachment folding of the Phanerozoic sedimentary cover (McQuarrie, 2004; Sherkati et al, 2006; Jahani et al, 2007; Mouthereau et al, 2007; Vergés et al., 2011a), as well as by a significant contribution of reactivated faults in the crystalline Precambrian basement, inherited from Permo-Triassic Neo-Tethys rifting During the Arabia-Eurasia collision, the tectonic evolution of the Zagros Fold Belt was shaped by the interplay of thin-skinned detachment folding of the Phanerozoic sedimentary cover (McQuarrie, 2004; Sherkati et al, 2006; Jahani et al, 2007; Mouthereau et al, 2007; Vergés et al., 2011a), as well as by a significant contribution of reactivated faults in the crystalline Precambrian basement, inherited from Permo-Triassic Neo-Tethys rifting (Figs. 1B and 2) (Jackson et al, 1981; Berberian, 1995; Talebian and Jackson, 2004; Mouthereau et al, 2006, 2007; Karasözen et al, 71 2019).
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