Late Cenozoic Exhumation and Basin Capture in the Eastern Talesh–Western Alborz (NW Iran): Insights From Low‐Temperature Thermochronology and Thermo‐Kinematic Modeling

Abstract

The NW‐SE‐oriented Eastern Talesh and Western Alborz Mountains of the Arabia‐Eurasia collision zone have constituted an efficient orographic barrier to northerly Caspian Sea moisture transport since the Early–Middle Miocene, resulting in pronounced rainfall and surface‐process gradients. Nevertheless, low‐temperature thermochronology indicates disparate orogen‐parallel and orogen‐perpendicular patterns of long‐term exhumation that do not follow the expected climatic gradients. West of the Lahijan lineament (LL), a suspected transverse NNE‐SSW‐striking, left‐lateral strike‐slip fault, south‐vergent thrusting dominates with <4 km of exhumation across the wetter northern flanks and >4 km across the arid southern flank. This reverse behavior with respect to the precipitation gradient, suggests that orographic precipitation alone cannot lead to the growth of new tectonic structures. Conversely, east of the LL, north‐vergent thrusting and superposed erosional processes resulted in >4 km of exhumation along the wetter northern orogenic flank. There, the lack of outward orogenic growth, together with protracted Miocene thrusting, suggests a balance between erosion and uplift. This structural setting (north‐dipping faults to the west and inward‐dipping faults to the east) may be inherited from the opening of the South Caspian Basin. Importantly, the structural boundary between the two areas (LL) has been exploited by deep incision and headward erosion by the Sefid Rud river. Thermo‐kinematic Pecube modeling supports a causal link notion between the formation of the Sefid Rud valley and base‐level fall in the Caspian Sea (∼5.5–3.2 Ma). Sea‐level lowering promoted fluvial incision that breached the Alborz‐Talesh range and integrated upstream basins into the regional drainage network.