The Miocene subsidence pattern of the NW Zagros foreland basin reflects the southeastward 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 resulted from the Cenozoic convergence and subsequent collision between the Arabian and Eurasian plates. The associated Neogene foreland basin includes ∼3–4 km of synorogenic, mostly nonmarine, clastic sediments, suggesting a strongly subsiding basin inconsistent with the adjacent moderate topographic load. To explain such a discrepancy, we assessed the magnitude of the basin's subsidence with respect to the effect of the surface load and dynamic topography. The lower Miocene isopach map of the Fatha Formation displays a longitudinal depocenter aligned with the orogenic trend. In contrast, the middle–upper Miocene maps of the Injana and Mukdadiya formations illustrate a focused depocenter in the southeastern region of the basin. This rapid basin subsidence in the southeast during the middle–late Miocene was coeval with the Afar plume northward flow 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 combined loads of the surface topography and the subducting slab during the early Miocene and was affected by dynamic topography due to the Neotethys horizontal slab tear propagation during the middle–late Miocene. This tear propagation was associated with a northward mantle flow above the detached slab segment in the NW and a focused pull on the attached portion of the slab in the SE.