An alternative dynamic mechanism for syncollisional magmatism

Abstract:

The European Alps is the place where the hypothesis of “slab breakoff” was first proposed to explain syncollisional magmatism (von Blanckenburg and Davies, 1995). In the “slab breakoff” model, subducted oceanic lithosphere detaches from the light continental lithosphere due to the buoyancy and can trigger the following magmatism by thermal perturbations. This hypothesis has been widely employed to interpret the syncollisional and post-collisional magmatism in the orogens world widely. However, recent seismic tomography studies (e.g., Zhao et al., 2016) demonstrate that the downdip slab continuity beneath the central Alps, ruling out the hypothesis of slab breakoff to explain Cenozoic Alpine magmatism. The seismic observations imply an alternative dynamic mechanism is demanded to explain the syncollisional and post-collisional magmatism in the central Alps.

Here we present a 2D thermomechanical numerical models to study the geodynamic evolution processes of thermal perturbations within continental subduction zones. We test the influence of some parameters including the dipping angle of subduction, the age and width of oceanic plates, push force, density contrast between oceanic and continental lithosphere and the thickness of continental lithosphere. The results show that the slab breakoff can occur at most cases. But an alternative dynamic mechanism of crust-mantle decoupling of continental plate can also introduce the similar thermal perturbation and is a potential cause for syncollisional and post-collisional magmatism. This mechanism can reconcile both the seismic observation and the geochemical diversity of the Cenozoic magmatism in the Apennines domain.

References

Ji W. Q., Malusà M. G., Tiepolo M., Langone A., Zhao L., Wu F. Y. (2019). Synchronous Periadriatic magmatism in the Western and Central Alps in the absence of slab breakoff, Terra Nova, doi: 10.1111/ter.12377.

Von Blanckenburg F., Davies J.H. (1995). Slab breakoff: A model for syncollisional magmatism and tectonics in the Alps, Tectonics, 14, 120-131.

Zhao L., Paul A., MalusàM. G., Xu X., Zheng T., Solarino S., Guillot S., Schwartz S., Dumont T., Salimbeni S., Aubert C., Pondrelli S., Wang Q., Zhu R. (2016). Continuity of the Alpine slab unraveled by high-resolution P-wave tomography, J. Geophys. Res., 121, 8720-8737, doi: 10.1002/2016JB013310.