Author name: Lukáš Ackerman

Evolution and Structure of the European Variscan Lithospheric Mantle

Tectonically emplaced peridotites and mantle xenoliths present complementary aspects of the evolution of the Variscan lithospheric mantle. The former have diverse origins and document complex histories of melt–rock reactions, exhumation along various pressure–temperature–time (P–T–t) paths, and emplacement into the crust, unravelling plate boundary evolution during Variscan subduction and collision. Mantle xenoliths exhumed by Cenozoic volcanism reveal ancient partial melting and mostly post-Variscan metasomatism episodes. Yet, their coarse-grained textures potentially record Variscan deformation. Dominantly belt-parallel fast seismic directions of the in situ Variscan lithospheric mantle may record flow normal to the convergence direction, but parallel to the boundaries of the Baltica and Avalonia blocks in central Europe, and to the main strike-slip faults and late extension in the Massif Central and Iberia.

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Deforming the Upper Mantle—Olivine Mechanical Properties and Anisotropy

The interior of the Earth remains our last terra incognita, inaccessible to direct observations. Our understanding of the deformation of the mantle, which shapes our planet through convection and plate tectonics, is based on analysis of: (1) rare mantle rocks carried to the Earth’s surface by volcanic or tectonic processes, (2) the consequences of this deformation on the planet’s surface, and (3) geophysical data. These observables combined with laboratory experiments and numerical modeling imply that olivine deforms via the motion of defects within its crystalline structure and along grain boundaries. Ductile deformation by these crystal-scale processes results in anisotropic propagation of seismic waves, which allows us to probe upper-mantle deformation at scales of tens to hundreds of kilometers.

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December 2025 --The Variscan Orogeny in Europe – Understanding Supercontinent Formation

The Variscan orogen formed between 380 and 300 million years ago through several accretionary and collisional cycles, culminating with the construction of the Pangea supercontinent. This process occurred via sequential opening and closure of oceanic basins, synchronous detachment of Gondwana derived continental ribbons, and their outboard amalgamation onto the Laurussia margin. The Variscan orogen is rather unique compared with other orogenic belts on Earth: its overthickened and dominantly magmatic crust in the central belt, surprisingly minor mantle involvement in the magmatic and geodynamic processes, coherent and pulsed magmatism along the collision suture, and its complex accretionary history. Because its final product, Pangea, is the youngest and best-understood supercontinent on Earth, the Variscan orogeny offers clues for understanding the mechanisms of supercontinent formation.