Saucer-shaped sill with lobate morphology revealed by 3D seismic data: implications for resolving a shallow-level sill emplacement mechanism

Abstract

We use 3D seismic data to describe the 3D geometry of a large igneous intrusion, the Solsikke Compound Sill, and address a number of issues related to sill emplacement. The Solsikke Compound Sill formed by amalgamation of a number of sills and exhibits a complex internal morphology dominated by saucer-shaped depressions and linear discontinuities. One of the saucer-shaped sub-elements of the compound sill, the Solsikke Lobate Sill, has a previously unrecognized morphology. It has a basal feeder and consists of a bifurcating network of interlinked lobe-shaped sill segments. We propose two models for the development of this intrusive style based on analogues from igneous systems and hydrofracturing experiments. The lobate pattern indicates that the Solsikke Lobate Sill was fed at its deepest point and adopted its geometry through outwards and upwards propagation. The feeder location is coincident with a fault intersection, suggesting that magma transport from the underlying source exploited the zone surrounding the intersection.