Evolution of the of Variscan orogenic mantle root in Europe viewed through combined analysis of tectonic models and mantle xenoliths

The European Variscan orogen (EVO) originated through tectonic accretion of few continental ribbons followed by collision of Gondwana and Laurussia, including docking of mantle parts of incoming terrains to the mantle wedge. At the late- and post-orogenic stage, the thickened orogenic root (Moho depth ca 55-60 km) flattened by lateral crustal flow and gravitational collapse [1], although this was not uniform across the EVO. In the Bohemian Massif, the crust is still fairly thick (ca. 35 km) and the impact of gravity-driven lateral flow of partially molten orogenic root was rather limited [2]. In contrast, the geology of French Massif Central (FMC) reflects the importance of lateral flow of the partially molten crustal orogenic root and its exhumation in crustal-scale domes beneath low-angle detachments. Where flattening occurred, it produced a relatively flat Moho at ca 30-32 km depth [3]. Thus, the lithospheric and asthenospheric mantle underlying the orogen must have been exhumed by 20-30 km.

The mantle parts of the EVO are sampled – as peridotite xenoliths – by numerous Cenozoic alkaline lavas of the Central European Volcanic Province. Despite locally strong Cenozoic metasomatic overprint, these xenoliths offer the opportunity to decipher the evolution of lithospheric mantle from which they come [4] including whether the xenoliths can constrain which parts of the Variscan orogen escaped delamination.

Slices of Variscan “orogenic peridotites”, attached to the growing orogen, now occur in the exposed basement “massifs”. They usually belong to the peridotite garnet facies (e. g. [5]), whereas the peridotite xenoliths occurring in Cenozoic lavas are exclusively spinel peridotites [6], confirming that large part of lithospheric mantle underlying EVO was exhumed from garnet- to spinel-facies P-T conditions. This decompression is recorded by spinel-pyroxene symplectites after garnet in some xenoliths, such as at Montboissier in the northern FMC domain.

Indeed, the xenoliths sampling large parts of the EVO lithospheric mantle are clinopyroxene-poor and depleted in major melt-mobile elements, suggesting that they represent lithospheric mantle fragments tectonically attached to the orogen root during orogenesis (“Variscan orogenic mantle” of [5]) which escaped subsequent delamination.

Our analysis suggests that lithospheric mantle evolution deciphered from xenoliths, if combined with geological data on crust evolution, allow to elaborate more pertinent tectonic-geodynamic models of EVO.

Funding. This study originated thanks to the project of Polish National Centre of Research 2021/41/B/ST10/00900 to JP.

[1] Vanderhaeghe, O., Laurent, O., Gardien, V.Moyen, J.-F., Gébelin, A., Chelle-Michou, C., Couzinie, S., Villaros, A., Bellanger, M., 2020. BSGF-Earth Sciences Bulletin 191, 25.

[2] Schulmann, K., Lexa, O., Janoušek, V., Lardeaux, J.M. and Edel, J.B. 2014. Geology, 42, 275–278

[3] Artemieva, I., Meissner, R., 2012. Tectonophysics 530-531, 18-49.

[4] Puziewicz, J., Aulbach, S., Kaczmarek, M.-A., Ntaflos, T., Matusiak-Małek, M., Ziobro-Mikrut, M., Gerdes, A., 2025. Lithos 494-495, 107908.

[5] Kubeš, M., Čopjaková, R., Kotková, J., Ackerman, L., Haifler, J., Výravský, J., Holá, Škoda, R., Leichmann, J., 2024. Journal of Petrology 65, egae108.

[6] Puziewicz, J., Matusiak-Małek, M., Ntaflos, T., Grégoire, M., Kaczmarek, M.-A., Aulbach, S., Ziobro, M., Kukuła, A., 2020. Lithos 362-363, 105467.