High-density eclogitic are formed in subduction zones, but they are rare at the surface of the Earth. Nevertheless, seismic data demonstrates the presence of large amounts of eclogites at the base of the crust in all regions, including cratons. The role of eclogites in the geological evolution may therefore be undervalued, and the amount of eclogitic material in cratons may generally be underestimated globally.

A new seismic profile across the central Lhasa terrane in Tibet shows that newly formed crust may be fully felsic to Moho at 80 km depth. This finding indicates a new process for formation of continental crust, whereby newly formed lower crust immediately transforms into high-density eclogitic rocks, which delaminate each time they exceed a critical volume!

Based on seismic data, we show that eclogite formation and associated delamination of lower crust caused the emergence of onshore areas above sea level at the onset of the Phanerozoic, which enabled the widespread explosion in onshore life and explains the related Neoproterozoic Oxidation event.