Microstructural evolution and seismic anisotropy of upper mantle rocks in rift zones. Geologica Ultraiectina (300)

This thesis investigates field-scale fragments of subcontinental upper mantle rocks from the ancient Mesozoic North Pyrenean rift and Plio-Pleistocene xenoliths from the active Baja California rift, in order to constrain the deformation history of the uppermost mantle. The main focus of the study is to examine the significance of fine-grained mylonitic shear zones for the mechanical and seismic properties of the mantle lithosphere beneath rift zones. It is concluded that the development of fine-grained mylonitic shear zones in the upper mantle is an important process of lithosphere weakening during continental rifting.