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From the following article: a, Conceptual models for the different phases of extension based on observations from the Alpine and Iberia/Newfoundland margins. They are set apart by different styles of deformation. The stretching mode (A) is characterized by listric faulting and a differential subsidence of half-grabens exemplified by the Monte Generoso basin12. The thinning mode (B) is the least documented of the modes but it can be characterized by maximum thinning of the lithosphere and the presence of a major ductile shear zone (Pogallo shear zone21) accommodating differential motion (up to 10 km upward) between the upper crust and the lower crust/upper mantle. It is accompanied by not much uplift of the rift flanks and subsidence in the hanging wall. The exhumation mode (C) is well documented and distinguished by the exhumation of serpentinized upper mantle from less than 10 km depth along a downward-concave fault. b, Modelled evolution during lithospheric extension. The plastic strain (brittle deformation) and viscosity field are plotted for the different phases of the modelled evolution of the lithosphere. Note the similarity between the observed and modelled structures. The stress envelope is plotted for a given depth profile (dashed lines for 36 km of extension). For each viscosity field the Mohorovic boundary is shown by a white line. The letter H indicates the hanging block discussed in the main text. c, Schematic representation of the temporal and spatial evolution of the three consecutive phases of rifting leading to break-up and seafloor spreading. |
