Peak convergence rate controls crustal thickness in collisional orogens over 500 million years
摘要
Whether the speed of plate convergence dictates the ultimate thickness and structural style of mountain belts remains poorly quantified over long timescales. Here I test the hypothesis that peak convergence rate is a primary control on crustal thickening in collisional orogens. I integrate paleomagnetic, geochronological, geophysical, and tomographic data within a kinematic modeling framework (GPlates) to reconstruct the tectonic evolution of three mountain belts spanning 500 Myr and a ten-fold range of convergence velocities: the Appalachians (2–4 cm/yr), the Urals (1.5–2 cm/yr), and the Himalayan system (15–20 cm/yr pre-collision). My reconstructions reveal a power-law relationship between peak convergence rate and maximum crustal thickness: T_c = 20.5·v^0.48 (R2 = 0.92, p < 0.001), where T_c is maximum crustal thickness (km) and v is peak convergence rate (cm/yr). Slow convergence (≤ 4 cm/yr) produces thin-skinned thrust belts with crustal thicknesses of 35–50 km and limited post-orogenic exhumation (0.03–0.06 mm/yr). Fast convergence (> 15 cm/yr) drives deep underthrusting, duplexing, and crustal thickening to > 80 km. Mantle tomography reveals that slow orogens either lack deep slab remnants or preserve only diffuse slab graveyards, whereas the fast Himalayan collision has a coherent slab penetrating into the lower mantle. These results provide a quantitative, multi-orogen test that convergence rate is a first-order predictor of orogenic architecture and preserved crustal root thickness.