The Léon region in France offers a window into the dramatic geological processes that shaped continents. Studying ancient rocks called eclogite, we uncovered a history of magma generation, deep burial and rapid crustal movement between 390 million and 300 million years ago. The area was shaped by subduction dynamics, where shifting tectonic plates stretched and compressed the crust. These findings help us understand how ancient geological processes continue to influence the Earth’s surface today.