Old orogen - young topography: Characterizing styles of late Cenozoic uplift and exhumation in the European Variscan belt

Abstract

Outcropping remnants of the Variscan orogen in Central Europe have experienced relief rejuvenation since the Miocene. Several modern Variscan massifs feature mountainous topography although they were leveled in the Permian and are far from active plate boundaries. Renewed uplift created mean elevations exceeding 1000 m and is attributed to intraplate processes such as mantle plumes, continental rifting, and lithospheric buckling. However, constraining these mechanisms remains challenging due to conflicting data, including high elevations with low uplift rates, steep river profiles with low erosion rates, and cooling ages exceeding 200 Ma.

This study investigates the unique topographic and erosional signatures associated with mantle-related processes. We combine orogen-wide morphometric analyses with new compilations of short-term catchment-wide erosion rates and long-term exhumation rates from low-temperature thermochronology. These results are tested against predictions from a novel 1D landscape evolution model incorporating flexural isostasy.

Our findings reveal that topographic expressions, but also erosional and denudational patterns are unique for each geodynamic process (i.e., mantle plume and rifting) and can be used as proxies to decipher and characterize the underlying geological drivers. Whereas mantle plumes induce a dome-shaped topography with high erosion rates at the margins and a low-relief, low erosion rate central surface, graben subsidence is accompanied by the uplift of pronounced asymmetric rift flanks, which is reflected in spatial variable erosion rates and drainage divide instability. Our analyses show that these inherently transient landscapes differ from collisional orogens, restricting these non-orogenic mountain ranges to transition directly from prematurity to decay.