Influences of slab breakoff on foreland basin architecture: inferences from stratigraphic forward modelling

One of the major tectonostratigraphic characteristics of foreland basins is the transition from deep marine (i.e. flysch) to terrestrial (i.e. molasse) depositional settings. Several mechanisms have been proposed to influence this flysch-to-molasse transition, including slab breakoff beneath the adjacent mountain range. However, this coupling has not yet been assessed quantitatively. We hypothesize that isostatic rebound following slab breakoff can lead to a spike in tectonic uplift of the orogen, resulting in increased sediment supply as well as uplift of the foreland basin, thereby causing shallowing.

This study aims at investigating whether slab breakoff leaves a stratigraphic fingerprint foreland basin stratigraphic architecture. To this end, we combine 2D geodynamic modelling of slab breakoff with Alpine-inspired rheologies with forward stratigraphic modelling using GPM (Geological Process Modelling) software. In this context, we extract subsidence and uplift velocities along 2D profiles during slab necking- breakoff to account for (1) fast/slow breakoff and (2) different slab bending angles. Second, the extracted velocity fields are used as input for creating forward stratigraphic models (FSM), in which eustatic sea level changes are introduced to test whether slab break-off has a first-order control on foreland basin sedimentation. Erosion, transport and deposition of sediments are modelled as diffusional processes (i.e. gravity driven).

Preliminary results indicate that a pulse in sediment supply corresponds to onset of slab necking whereas breakoff yields a small pulse instead. This could imply that already during necking the orogen is isostatically uplifted to such a degree that sediment supply towards to foreland basin increases significantly.