Lateral magma migration through interconnected sills: Evidence from analogue modeling

Abstract

We explore the capability of interconnected sills to transport magma in the shallow crust, as well as the effect of simultaneous and temporally separated multiple magma emplacement on deformation pattern. We analyze this process through analogue models run with synchronous or diachronous magma injection from different, aligned inlets. Experimental results show that the position and activation in time of multiple injection points strongly influence model evolution. In case of synchronous injection at different inlets, intrusions and associated surface deformation are elongated. Forced folds and annular bounding reverse faults are quite elliptical, with the main axis trending sub-parallel to the magma input alignment. Diachronous injection from different sources would instead favor the lateral migration of magma rather than the vertical growth of intrusions. This evolution promotes the development of interconnected intrusions, and suggests that the deformation observed at surface does not necessarily reflect the location and activation timing of their feeders. Overall, our observations have significant implications for the kinematic evolution of sill complexes, timing of intrusion and associated deformation, raising the possibility that interconnected sills may act as channels for long-range lateral magma transport through a succession of sill-fed emplacement events. Model results also suggest that caution should be taken when trying to infer the feeding areas on the basis of the deformation features observed at the surface or in seismic profiles.