Tectonic stress controls saucer-shaped sill geometry

Abstract

Saucer-shaped sills are common in sedimentary basins worldwide. The saucer shape relates to asymmetric stress distributions at the sill-tip during intrusion caused by bending of the overburden. Most saucer-shaped sill models are conducted without tectonic stress. Model results are poorly correlated with natural sills in that: (1) modelled saucers are much steeper than natural sills; and (2) natural sill inclines are convex in profile whereas modelled saucer inclines are concave. We present finite element simulation of initially horizontal sill emplacement for a range of tectonic stress (sigma_r) conditions, from mild horizontal tension (sigma_r<0), to horizontal compression (0