Inelastic damage as a mechanical precursor for the emplacement of saucer-shaped intrusions
Published by: Øystein Thordén Haug, Olivier Galland, P. Souloumiac, Alban Souche, Frank Guldstrand and Tobias Schmiedel.
Shear dissipation maps (damage, given by energy dissipation in kJ) within model domain for sills (white line) with diameter of 0.5 km (upper), 6 km (middle), and 20 km (lower).
Sill intrusions with a characteristic saucer shape are observed in many sedimentary basins worldwide. Previous models of their emplacement usually assume a purely elastic host-rock rheology. However, a growing number of eld observations show a non-negli- gible amount of faulting and associated plastic deformation related to their emplacement. We use a rigid-plasticity approach to study the conditions for nonelastic deformation and the damage patterns related to sill emplacement. The results show that the characteristic saucer shape is ubiquitously reproduced using this approach. By varying the sill diameter, we observe that the shape of the dam- age zones changes from straight for small diameters to curved for large ones. The overpressure of the sill is seen to decrease rapidly with increasing sill diameter, suggesting that longer sills are more prone to undergoing plastic deformation. In contrast to previous studies, which assume that an asymmetric stress eld de ects the propagating sill tip, our models suggest that saucer-shaped sills are created due to shear failure caused by an in ating at sill. This implies that plastic damage is a precursor for the emplacement of saucer-shaped sills.