Brittle-ductile_transition_zone
Brittle–ductile transition zone
Strongest part of the Earth's crust
The brittle-ductile transition zone (hereafter the "transition zone") is the zone of the Earth's crust that marks the transition from the upper, more brittle crust to the lower, more ductile crust.[1] For quartz and feldspar-rich rocks in continental crust, the transition zone occurs at an approximate depth of 20 km,[2] at temperatures of 250–400 °C. At this depth, rock becomes less likely to fracture, and more likely to deform ductilely by creep because the brittle strength of a material increases with confining pressure, while its ductile strength decreases with increasing temperature.