Saucer-shaped intrusions: Occurrences, emplacement and implications

Magmatic intrusions and fluidized injected sands represent the two main types of sheet intrusions in the Earth's crust. In this paper we show that both intrusion types often display a saucer-like geometry, as revealed by 3D seismic imaging and field observations. Saucer-shaped intrusions are fairly common in sedimentary basins, as for example offshore in the Norwegian and North Sea basins and onshore in the Karoo Basin of South Africa. The formation of the saucer geometry is controlled by the low-viscosity of the injected fluid and by the interaction between a growing shallow hydraulic fracture and overburden deformations. Statistics gathered from observations and modelling show a linear relationship between the depth of emplacement and the size of the saucer-shaped intrusions. We anticipate future cross-disciplinary studies aiming to discover other occurrences of saucer-shaped intrusions and to identify the physical processes controlling the development of this fundamental geometry.