Importance of Eclogites from Cratonisation to the Phanerozoic Explosion of Onshore Life

Eclogite formation from lower crustal rocks requires high pressure at relatively low temperature in the presence of water. Due to the high temperature regime in the early Earth and the sparse observations of eclogitic rocks at the surface, it is generally expected that such rocks are rare in cratons. Our recent results show that large amounts of eclogitic lower crustal rocks are present below the seismic Moho in the Baltic Shield¹. Such eclogites in various metamorphic grades may explain the high topography of the Scandes mountain range in northern Fennoscandia². Our findings suggests that the amount of sub-Moho eclogite can be generally underestimated globally!

Eclogitization may also play a major role in plateau formation in Tibet, where new addition of mafic underplate to the overthickened crust may immediately transform into eclogite, which founder each time the eclogite layer exceeds a critical thickness³. The whole continental crust in the central Lhasa Block has low seismic velocity (<6.7 km/s), which indicates that this thickest crust on Earth is felsic down to the Moho at 80 km depth, explaining half the present topography by isostasy. However, underplating and partial melt in the crust are also required to explain the high elevation of the Tibetan Plateau and other major plateaux worldwide⁴.

By interpretation of >18,000 km of seismic profiles, we document that a mafic crustal layer is generally preserved in Proterozoic orogens but absent in Phanerozoic orogens⁵. This indicates a change in the global subduction style at the onset of the Phanerozoic, which caused massive eclogitization of lower crust in orogens and recycling of the eclogitic rocks into the mantle. The resulting buoyant felsic crust lifted continents above sea level, which enabled onshore life to develop, thus explaining the Neoproterozoic oxidation event and the explosion of life in the Phanerozoic.

1. Buntin, S. et al. Long-lived Paleoproterozoic eclogitic lower crust. Nature Communications 12 (2021). https://doi.org/10.1038/s41467-021-26878-5

2. Kahraman, M. et al. Northern Scandinavian mountains supported by a low-grade eclogitic crustal keel. Nat Commun 16, 606 (2025). https://doi.org/10.1038/s41467-025-55865-3

3. Wang, G., Thybo, H. & Artemieva, I. M. No mafic layer in 80 km thick Tibetan crust. Nature Communications 12, 1069 (2021). https://doi.org/10.1038/s41467-021-21420-z

4. Zhou, Z., Thybo, H., Artemieva, I. M., Kusky, T. & Tang, C. C. Crustal melting and continent uplift by mafic underplating at convergent boundaries. Nat Commun 15, 9039 (2024). https://doi.org/10.1038/s41467-024-53435-7

5. Xia, B., Artemieva, I. M. & Thybo, H. Phanerozoic emergence of global continental collision and onset of massive crustal eclogitization. Geology 53 (2025). https://doi.org/10.1130/g52647.1