Modelling of lithospheric history-dependent stretching from continental rifts to passive margins formation
thesisposted on 15.05.2017 by Salerno, Vittoria Morena
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Under the effect of divergent forces, continental lithosphere deforms into continental rifts, where stretching is either diffused over large areas or localized in narrow straining zones. Existing models have probed the role of initial lithospheric rheological layering, geothermal gradients and stretching rates on continental rifting evolution. While the boundary conditions imposed by the diverging margins relate to the rifting phase, the initial conditions are inherited features. Many continental rifts underwent several extensional phases, showing a variety of deformation style. Such complexities are not easily explained by a single stretching phase; instead these might find better explanation considering a polyphase rifting history. In this thesis, I address the role of episodic stretching on the long-term evolution of continental rifts. I explore two main types of rifting histories: 1) Rifting-Cooling-Rifting and 2) Rift –Rift. The first type aims to analyse the general aspect of the rifting evolution where rifting phases are intermitted by a cooling stage, which allows for geothermal re-equilibration, and consequently lithosphere can regain its original thickness. In this case, the lithosphere attains a different rheological layering, and this affects subsequent rifting. Alternating stretching velocities between the first and second rifting event generates a series of rifting histories. In the second case, I propose a possible solution for the evolution of the Sirte Basin, providing an alternative explanation to its structuring. In particular I attempt to understand if the rifting history could have played a primary effect on the shifting in rifting mode over time (from wide to narrow). I use numerical modelling to investigate the development of rifting patterns during polyphase lithospheric extension. The models show that the time-dependent boundary conditions have a fundamental control on the tectonic rifting style and its evolution. The formation of narrow and wide rifts, and their shift in time might be strongly related to the cooling events and changing in boundary conditions during rifting history.