Abstract
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, seismic reflection 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 a basin, where a magmatic underplate body impinges on thinned crust. Magma is transported through the crystalline crust through dykes. Seismic data and published geochemistry indicate that magma is supplied from a magmatic underplate without perceptible storage in crustal magma chambers and crustal assimilation. As magma enters the sedimentary basin, it forms distributed, bowl-shaped sill-complexes throughout the basin. Large magma volumes in sills (4–20 times larger than the Skaergaard Intrusion) and the presence of 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 10 km 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.Supplementary material: An uninterpreted and unwarped version of the seismic line in Fig. 4 (DR1), a spreadsheet showing thickness of sills and width of dykes in the study area (DR2), and assumptions and calculations of magma volume (DR3) are available at https://doi.org/10.6084/m9.figshare.c.5670470
Highlights
Sill-complexes are interconnected magma conduits that are broadly parallel to stratigraphy, transgress upwards and transfer magma through the crust and in certain cases to eruption (e.g. Lorenz & Haneke 2004; Cartwright and Møller-Hansen, 2006; Jaxybulatov et al 2014; Schofield et al 2015; Eide et al 2017)
PT The igneous intrusions in the Jameson Land Basin are well-exposed in the sea cliffs on the west side I of Scoresby Sund (Fig 2), where they can be observed as dark, transgressive intrusive rocks R commonly 10 m thick, within the lighter Jurassic host rock (Fig. 3)
Based on the observations made from the Jameson Land Basin in East Greenland, we present a model for magma transport from the mantle, through the thinned crystalline crust and through the Jameson Land Basin (Fig. 10)
Summary
Sill-complexes are interconnected magma conduits that are broadly parallel to stratigraphy, transgress upwards and transfer magma through the crust and in certain cases to eruption (e.g. Lorenz & Haneke 2004; Cartwright and Møller-Hansen, 2006; Jaxybulatov et al 2014; Schofield et al 2015; Eide et al 2017). E Understanding the geometry of the magma transport system and physical controls on development PT of sill-complexes is valuable to map out the route of magma within upper crustal and basin E settings, understanding the propagation and architecture of sill-complexes is important to C interpret earthquake (e.g. Sigmundson et al 2010) and ground deformation data (e.g Pedersen and AC Sigmundsson, 2004; Galland 2012; Magee et al 2017) related to volcanic unrest Another area where understanding intrusion networks is important, is for utilization of geologic resources in intruded basins (e.g. hydrocarbons, groundwater, mineral resources, geothermal heat; e.g. Senger et al 2017, MacDonald et al 2001; Hayman et al 2021 and Elders et al 2014, respectively). This basin offers a unique opportunity to understand magma transport through the crust and sedimentary basin on scales from centimetres to tens of kilometres because 1) about 3 km of post-emplacement erosion (Mathiesen et al 2000, Hansen et al 2001) has dissected the mafic intrusions leading to extensive unvegetated outcrops where dykes (subvertical igneous sheets) and sills (broadly layer-concordant igneous sheets) can be readily investigated in large 10’s km scale outcrops (Figs 2, 3), 2) there is a well-constrained stratigraphy due to widespread outcrops and decades of surface and subsurface geological investigations (e.g. Surlyk et al 1973; Dam & Surlyk 1998, Ahokas et al 2014; Eide et al 2016, 2017, 2018; Guarneri et al 2017; Brethes et al 2018), 3)
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