Geochemical Evidence for Diachronous Uplift and Synchronous Collapse of the High Elevation Variscan Hinterland

Competing end‐member models for the late Paleozoic Variscan orogeny (ca. 360‐290 Ma) alternatively suggest moderate 2–3 km elevations underlain by relatively thin crust (55 km) that supported high 4–5 km elevations. We tested these models and quantified the crustal thickness and elevation evolution of the Variscan orogeny using igneous trace element geochemical proxies and geochronologic data. These data suggest that thick crust (55–70 km) capable of supporting 3–5 km elevations developed diachronously from east to west between ca. 350 and 315 Ma. Crustal thinning occurred from ca. 315 to 290 Ma across the orogen. Crustal thickness and elevation changes at ca. 340‐325 and 315‐290 Ma correspond with increases in silicate weathering recorded by Sr and Li isotopes, consistent with models in which silicate weathering of the Variscan orogen contributed to global cooling associated with the late Paleozoic ice age. Plain Language Summary It is debated whether the Variscan mountains at the core of the supercontinent Pangea had thick crust capable of supporting high topography and influencing past climate. We used trace element geochemical data from igneous rocks to estimate past crustal thickness and surface elevation. The data suggest a high elevation, Himalayan‐length mountain belt formed first in central Europe and expanded westward between 350 and 315 Ma. Crustal thickness and paleo‐elevation decreased across the entire mountain belt between 315 and 290 Ma indicative of orogenic collapse. Changes in Variscan surface elevation correspond with time periods of greater chemical weathering and global cooling, suggesting that tectonics may have influenced past climate. Key Points Sr/Y‐La/Yb ratios of igneous rocks quantitatively track Variscan crustal thickness and elevation Thick crust capable of supporting high elevations developed by ca. 350 Ma and expanded westward Results consistent with chemical weathering of the Variscan hinterland as a contributor to late Paleozoic environmental change