Granite regolith weathering in the Qinling Mountains: Geochemical signatures and pedogenic dynamics

Mountain regolith develops under strong topographic gradients, where chemical weathering and pedogenesis are dynamically coupled with erosion and lateral material redistribution. To examine how these interacting processes are expressed across contrasting geomorphic settings, six granite-derived profiles in the northern foothills of the Qinling Mountains, China, were investigated using physicochemical, geochemical, mineralogical, and petrographic analyses. Results indicate a relatively limited degree of chemical alteration, with Chemical Index of Alteration (CIA) values ranging from approximately 54 to 64. The petrographic and mineralogical results confirm that primary minerals (quartz, plagioclase, and K-feldspar) dominate the regolith, accompanied by illite and vermiculite clay assemblages. Mass transfer coefficients exhibit irregular vertical fluctuations and inter-profile heterogeneity, indicating strong external perturbations. Relatively immobile high field strength elements (HFSEs; e.g., Ti, Hf) are depleted in the surface and subsurface soil horizons relative to the deeper regolith, likely reflecting downward translocation and lateral export of fine particles. Overall, geochemical and mineralogical patterns, together with their variation among geomorphic positions, point to hillslope erosion and material redistribution as the principal geomorphic processes modifying the retention and redistribution of weathering products, while localized accumulation and vegetation-related biogeochemical cycling may further affect nutrient-element distributions. The investigated profiles therefore record non-steady-state weathering and pedogenesis rather than a uniformly progressive in situ weathering sequence. These findings highlight the importance of accounting for erosion-driven removal and redistribution when interpreting weathering intensity and pedogenic development in mountain environments.