Drainage Divide Migration on Asymmetrically Uplifted Horsts, Western Türkiye

The migration of a main drainage divide is pivotal in landscape evolution, providing key insights into how tectonic and erosional processes shape landscapes. However, the dynamics of divide migration in response to asymmetric uplift and erosion are not well constrained in natural settings compared to modeling studies. This study examines drainage divide migration in response to gradient in uplift and erosional contrast in the horst systems of the western Anatolia Extensional Province, Türkiye. Using 11 new cosmogenic ¹⁰Be-derived erosion rates and topographic metrics, we demonstrate that differing positions of main drainage divides result from variations in uplift gradient and erosional contrast, despite the simultaneous exhumation of horsts under the same extensional regime. The findings show that Madran Horst's main drainage divide is closer to its more uplifted eastern flank and is controlled by a higher uplift gradient between the flanks. The higher erosion rates in the eastern flanks suggest a quasi-steady-state equilibrium in which the high erosional contrast between the flanks and the gradient in uplift is already balancing each other as supported by Gilbert metrics in contrast to χ. In contrast, the Karıncalıdağ Horst's main drainage divide is approaching its geometric center supported by closer values in χ anomalies, stability in Gilbert metrics, and a decreasing gradient in uplift between flanks. Although the main drainage divide is close to the geometric center, higher erosion rates in the eastern flank suggest ongoing erosion-driven migration. This study provides empirical evidence for drainage divide migration driven by asymmetric uplift and erosional contrast.