Miocene evolution of the NW Zagros foreland basin reflects SE-ward propagating tear of the Neotethys slab

Abstract. Tectonic processes resulting from solid Earth dynamics control uplift and generate sediment accommodation space via subsidence. Unraveling the mechanism of basin subsidence elucidates the link between deep Earth and Surface processes. The NW Zagros fold-thrust belt results from the Cenozoic convergence and subsequent collision between the Arabian and Eurasian plates. The associated Neogene foreland basin includes ~4 km of syntectonic nonmarine clastic sediments, suggesting a strongly subsiding basin inconsistent with the adjacent topographic load. To explain such discrepancy, we assessed basin subsidence with respect to the effect of surface load and dynamic topography. The isopach map of the Fatha Formation during the middle Miocene displays a longitudinal depocenter aligned with the orogenic trend. In contrast, the maps of the Injana Formation and Mukdadiya Formation during the late Miocene illustrate a focused depocenter in the southern region of the basin. The rapid subsidence in the south during the late Miocene was coeval with the Afar plume flow northward beyond the Arabia-Eurasia suture zone in the northwestern segment of the Zagros belt. Based on isopach maps, subsidence curves, and reconstructions of flexural profiles, supported by Bouguer anomaly data and maps of dynamic topography and seismic tomography, we argue for a two-stage basin evolution. The Zagros foreland basin subsided due to the load of the surface and the subducting slab during the early-middle Miocene and was later affected by the Neothethys horizontal slab tear propagation during the late Miocene. This tear propagation was associated with a northward mantle flow above the detached segment in the NW and a focussed slab pull on the attached portion of the slab in the SE.