No mafic layer in 80 km thick Tibetan crust   

This article presents the first evidence for an unusual type of crust in the Earth, observed in the Tibetan highlands. The crust is usually 30-45 km thick, and its lower half consists of dense rocks with very low silica content (mafic rocks). Our new seismic data from some of the thickest crust on Earth shows that only silica-rich rocks are present to depths of more than 80 km. This observation indicates that a hitherto unknown formation process has been active in the evolution of the Earth. Geologists have for long suspected that mafic layers in the lower crust may transform into very dense material (eclogites) by metamorphic processes, and that such high-density layers may sink into the mantle by a process called delamination. The new finding indicates that delamination may happen while the crust is being formed when the newly formed crust becomes super-thick.

Wang, G., Thybo, H., Artemieva, I. M., 2021. No mafic layer in 80 km thick Tibetan crust. Nature communications, 12(1), 1-9