Igneous sheet-complexes transport magma through the crust, but most studies have focused on single segments of the magma-transport-system or have low resolution. In the Jameson Land Basin in East Greenland, reflection-seismic data and extensive outcrops give unparalleled constraints on mafic intrusions down to 15 km. This dataset shows how sill-complexes develop and how magma is transported from the mantle through sedimentary basins. The feeder zone of the sill-complex is a narrow zone below basin, where a magmatic underplate body impinges on thinned crust. Magma was transported through the crystalline crust through dykes. Seismic data and published geochemistry indicate magma was supplied from a magmatic underplate, without perceptible storage in crustal magma-chambers and crustal assimilation. As magma entered the sedimentary basin, it formed distributed, bowl-shaped sill-complexes throughout the basin. Large magma volumes in sills (4-20 times larger than the Skaergaard Intrusion), and few dykes highlight the importance of sills in crustal magma-transport. On scales smaller than 0.2 km, host-rock lithology, and particularly mudstone tensile strength-anisotropy, controls sill-architecture in the upper 10km of the basin, whereas sills are bowl-shaped below the brittle-ductile transition zone. On scales of kilometres and towards basin margins, tectonic stresses and lateral lithological changes dominate architecture of sills.
Scientific editing by Renjie Zhou