Torgeir Andersen on Ultrahigh-Pressure Metamorphism

Continental crust is buoyant, which is why continents stand high above the ocean floor. Yet rocks in western Norway contain microscopic grains of coesite, a form of quartz that forms only under pressures found about 100 km down. A slab of continent was dragged deep into the mantle, and then came back up.
In this episode, Torgeir Andersen, Professor Emeritus at the University of Oslo, explains how the rocks of Norway's Western Gneiss Region made that round trip some 400 million years ago, and why a few isolated diamond-bearing pods may record local overpressure rather than even greater depth.
Illustrations and full transcript: geologybites.com/torgeir-andersen