3-D seismic images of an extensive igneous sill in the lower crust

Geology 0091-7613 05 31 2019 08 01 2019 47 8 3-D seismic images of an extensive igneous sill in the lower crust T. Wrona Department of Earth Science, University of Bergen, Allégaten 41, N-5007 Bergen, Norway Norwegian Academy of Science & Letters (VISTA), Drammensveien 78, 0271 Oslo, Norway C. Magee Basins Research Group, Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK School of Earth and Environment, University of Leeds, Leeds LS2 9JT, UK H. Fossen Museum of Natural History, University of Bergen, Allégaten 41, N-5007 Bergen, Norway R.L. Gawthorpe Department of Earth Science, University of Bergen, Allégaten 41, N-5007 Bergen, Norway R.E. Bell Basins Research Group, Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK C.A.-L. Jackson Basins Research Group, Department of Earth Science and Engineering, Imperial College, Prince Consort Road, London SW7 2BP, UK J.I. Faleide Department of Geosciences, University of Oslo, P.O. Box 1047 Blindern, N-0316 Oslo, Norway Abstract

When continents rift, magmatism can produce large volumes of melt that migrate upwards from deep below the Earth’s surface. To understand how magmatism impacts rifting, it is critical to understand how much melt is generated and how it transits the crust. Estimating melt volumes and pathways is difficult, however, particularly in the lower crust where the resolution of geophysical techniques is limited. New broadband seismic reflection data allow us to image the three-dimensional (3-D) geometry of magma crystallized in the lower crust (17.5–22 km depth) of the northern North Sea, in an area previously considered a magma-poor rift. The subhorizontal igneous sill is ∼97 km long (north-south), ∼62 km wide (east-west), and 180 ± 40 m thick. We estimate that 472 ± 161 km3 of magma was emplaced within this intrusion, suggesting that the northern North Sea contains a higher volume of igneous intrusions than previously thought. The significant areal extent of the intrusion (∼2700 km2), as well as the presence of intrusive steps, indicate that sills can facilitate widespread lateral magma transport in the lower crust.

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