Crustal Melting and the Flow of Mountains

As the continental crust thickens during mountain building, it can become hot enough to start melting, leading to a profound reduction In its strength. Melt-weakened crust can flow outward or upward in response to the pressure gradients associated with mountain building, and may be transported hundreds of kilometres laterally as mid-crustal channels. In the Himalayan-Tibetan system, melting began about 30 million years ago, and widespread granite intrusion began at 20-23 Ma. Geophysical data indicate that melt is present beneath the Tibetan plateau today, and deeply eroded mountain belts preserve evidence for melt-enhanced ductile flow in the past. Flow of partially molten crust may limit the thickness and elevation of mountain belts and has influenced the deep structure of continents.