Steep bending of continental lithosphere without its stretching or plate collision: an indication for lithospheric failure and phase transitions

The Black Sea and Peri-Caspian basin include steep slopes which are 4–10 km high and only 20–30 km wide. They formed without extension-related normal faulting beneath the slopes and convergence in the adjacent regions. In the Peri-Caspian basin a steep bending of the lithosphere was associated with rapid crustal subsidence which evolved over a few million years. The large intensity and high rate of the deformations indicate a temporary loss of high rigidity in the lithospheric layer which occurred independently of plate-boundary-related processes. The origin of this phenomenon presents a special problem. A tentative explanation is that a lithospheric failure in cool intraplate regions can result from infiltration of volatiles from the asthenosphere and rapid metamorphism in mafic rocks in the lower crust.