Basin-scale architecture of deeply emplaced sill complexes: Jameson Land, East Greenland

Igneous sills are common components in rifted sedimentary basins globally. Much work has focussed on intrusions emplaced at relatively shallow paleodepths (0-1.5 km). However, due to constraints of reflection-seismic imaging and limited field-exposures, intrusions emplaced at deeper paleodepths (>1.5 km) within sedimentary basins are as not well-understood in regard to their emplacement-mechanisms and host-rock interactions. Results from a worldclass, seismic-scale outcrop of intruded Jurassic sedimentary rocks in East Greenland are presented here. Igneous intrusions and their host-rocks have been studied in the field and utilising a 22 km long “virtual outcrop” acquired using helicopter-mounted lidar. The results suggest the geometries of the deeply emplaced sills (c. 3 km) are dominantly controlled by host-rock lithology, sedimentology and cementation state. Sills favour mudstones and even exploit cm-scale mudstone-draped dune-foresets in otherwise homogeneous sandstones. Sills in poorly cemented intervals show clear ductile structures, in contrast to sills incemented units which only show brittle emplacement-structures. The studied host-rock is remarkably un-deformed despite intrusion. Volumetric expansion caused by the intrusions is almost exclusively accommodated by vertical jack-up of the overburden, on a 1:1 ratio, implying that intrusions may play a significant role in uplift of a basin if emplaced at deep basinal levels.