Hans Thybo

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 (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/s41467-021-26878-52. 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/s41467-025-55865-33. 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-z4. 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/s41467-024-53435-75. 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.

The processes causing the uplift of the world’s highest continental plateaux in Tibet, the Andes and East Anatolia are enigmatic. A number of tectonomagmatic processes are proposed, and it is generally believed that the crustal structure is the key to explaining their high topography. Key factors affecting the crustal structure include the metamorphic formation of eclogitic rocks from lower crustal material, underplating and partial melting of the crust.We show that the whole continental crust has low seismic velocity (

The role of magmatism in modulating continental breakup remains a topic of debate1. We present new, high-resolution 3D seismic reflection data from the South China Sea that reveals voluminous lower crustal magmatism occurred ~7–10 Myr before breakup along a >1,000 km long, NE–SW trending belt offset 100 km landwards of the eventual continental rupture. Through integration with numerical geodynamic models of continental extension, we show that a thermal anomaly associated with such lower crustal magmatic intrusion facilitate continental breakup. Specifically, our models show focused magma intrusion weakens the crust, promoting strain localization and migration that can lead to continental rupture 10’s–100’s km away from the site of initial magmatism.

The Earth CT initiative has been discussed during the International Symposium, DEEP-2018, DEEP-2021 and DEEP 2024. With the kicking off of SinoProbe II, it would be pushed forward in real soon or later. Deep Earth processes control the geological evolution, including the formation of natural resources, natural disasters, and large-scale environmental changes at the surface of the Earth. The Earth CT programme aims to globally construct long range profiles in wide corridors to image the lithosphere by integrative interpretation of geoscientific data. The programme will integrate data from structural geology and tectonic interpretation at global and continental scales, geochemical surveys in geotransect corridors to define their crustal and lithospheric composition, deep seismic reflection and refraction/wide-angle reflection profiling to identify crustal and upper mantle structure and composition, magnetotelluric(MT) sounding for the electrical structure, broadband passive seismic tomography techniques for global and regional velocity structure and receiver functions for crustal/upper mantle structure, as well as gravity and magnetic regional and global interpretation. Scientific drilling for deep earth sampling and detection of anomalous features in key tectonic belts will be based on the interpretation of the above data and will add substantially to the uniqueness of the global and regional interpretation. The aims of the project are to reveal the deep structure of the lithosphere, recognize the deep processes of plate movement and their control and influence on the surface system, explore energy and mineral resources at depth, and provide insight into geoscience frontier issues, such as the mechanisms controlling natural disasters and their intrinsic dynamics. The following approach has been supported by several societies, academic institutions and research facilities specializing in contourites, as well as proposed by Shuwen Dong, Larry Brown, Hans Thybo and many worldwide leading scientists.(1) To construct global “Big Cross” of the lithosphere by integration of intercontinental and regional geoscience transects based on reflection profiles.(2) Lithosphere geotransect and geosciences corridor in Critical Zones.(3) Global Array of BBS.

The mantle transition zone (MTZ) bounded by the 410-km discontinuity (d410) and 660-km discontinuity (d660), controls material and heat exchange between the upper and lower mantle. The phase transformations in MTZ are affected by subducting slabs that reach the transition zone by the exothermic phase transitions from olivine to wadsleyite around d410 and from wadsleyite to ringwoodite around 520 km depth (d520), as well as the endothermic phase transition from ringwoodite to post-spinel phases around 660 km depth which has long been considered as a likely cause of a viscosity increase below d660. However, how subducting slabs impact the mantle transition zone (MTZ) is debated. The Pacific-Asia subduction system is ideal for studying slab impact on the MTZ. It includes multi-stage subduction of the modern Pacific plate and the earlier Izanagi plate, and seismic tomographic models image flattening of the Izu-Bonin and Japan-southern Kurile slabs at the base of the MTZ. We calculate receiver function images of the MTZ based on data recorded by 322 broadband seismic stations in Northeastern China. We image the area of the flattened slab inside the MTZ but not the effects where the slab interacts with d410. Our results show that the d410 is flat and 5-10 km deeper than the global average within the area covered by our data and the average depth of d660 is about 670 km, which is consistent with previous results and may be explained by temperature-chemical effects. A complex d520 is clearly observed which we interpret as the top boundary of the flattened slab although it may also be caused by unstable temperature conditions.

The whole North Atlantic region has highly anomalous topography and bathymetry. Observations show evidence for anomalously shallow bathymetry in the ocean as well as recent rapid topographic change with onshore uplift close to the Atlantic coast and simultaneous subsidence of basins on the continental shelves, most likely throughout the Mesozoic. We present a geophysical interpretation of the whole region with emphasis on data relevant for assessing hypsometric changeMost of the North Atlantic Ocean has anomalously shallow bathymetry by up-to 4 km compared to other oceans. Bathymetry is elevated by up-to 2 km and follows the square-root-of-age model, except for the region between Greenland Iceland Faroe Ridge (GIF) and the Jan Mayen Fracture Zone as well as in the Labrador Sea to Baffin Bay. Heat flow follows with large scatter the square-root-of-age model in parts of the ocean and is anomalously low on the Reykjanes and Mohns spreading ridges. Near-zero free-air gravity anomalies indicate that the oceanic areas are generally in isostatic equilibrium except along the mid-oceanic ridges, whereas anomalously low Bouguer anomalies in the oceanic areas indicate low density in the uppermost mantle. Anomalously thick crust is observed along GIF and extends into the Davies Strait. There is no correlation between bathymetry and heat flow, which indicates that the anomalous bathymetry mainly is caused by compositional variation and isostatic compensation of low density continental lithosphere within the oceanic regions. The location of major oceanic fracture zones and continental fragments appears to be controlled by onshore structures.The onshore circum-Atlantic areas show rapid uplift close to the coast with rates of up-to 3 cm/yr. This is surprisingly mainly associated with strong positive free-air gravity anomalies, which would predict isostatic subsidence. Some parts of the high topography, however, appear supported by low-density anomalies below the seismic Moho. It is enigmatic that the presumed Archaean-Proterozoic continental Barents Sea region is submerged and includes deep sedimentary basins.

The Lofoten continental shelf is located at the edge of the Baltic Shield in the northeastern North Atlantic Ocean. It was formed during continental break up in early Eocene associated with intense magmatism, leading to large intrusions and basaltic volcanic rocks now hidden below Cenozoic sediments. The Lofoten shelf is relatively narrow.We present results of ray tracing model of seismic refraction/wide-angle reflection data along the offshore Silver Road profile across the Lofoten Shelf at the northeastern Baltic Shield. The ~300km long WNW/ESE trending offshore section between 63oN and 71oN profile is perpendicular to the coastline and extends a ~300km onshore section. Wide-angle seismic data obtained from air gun shots from the vessel Hakon Mosby along the whole offshore profile were recorded by 16 ocean bottom seismometers on the shelf, slope and oceanic environment as well as by 270 onshore seismic stations.The new offshore crustal velocity - depth model covers the anomalous and heterogeneous transition from shelf to oceanic lithosphere around the North Atlantic Ocean. The results will test existence of crustal root and magmatic intrusions along the offshore profile.