3D seismic reflection evidence for lower crustal intrusions beneath the Faroe-Shetland Basin, NE Atlantic Margin

Abstract

Lower crustal intrusion is considered a common process along volcanic or magma-rich passive margins, including the NE Atlantic Margin, where it is considered to have occurred during phases of Paleogene magmatism, prior to and during continental break-up between NW Europe and Greenland. Evidence of Paleogene magmatism is prevalent throughout the sub-basins of the Faroe-Shetland Basin (FSB) as extensive lava flows and pervasive suites of igneous intrusions. However, in contrast to other areas located along the NE Atlantic Margin, no lower crustal reflectivity indicative of lower crustal intrusions has been documented beneath the FSB. The nearest documentation of lower crustal reflectivity and interpretation of lower crustal intrusions to the FSB is NW of the Fugloy Ridge, beneath the Norwegian Basin of the Faroese sector. Despite this, the addition of magma within the lower crust and/or at the Mohorovičić discontinuity is thought to have played a role regarding Paleogene uplift and the subsequent deposition of Paleocene-Eocene sequences. Advances in sub-basalt seismic acquisition and processing have made significant improvements in facilitating the imaging of deep crustal structures along the NE Atlantic Margin. This study uses broadband 3D seismic reflection data to map a series of deep ( c. 14 to 20 km depth) high-amplitude reflections which may represent igneous intrusions within the lower crust beneath the central-northern Corona Ridge. We estimate that the cumulative thicknesses of the reflections may be over 5 km in places, which is consistent with published values of magmatic underplating within the region based on geochemical and petrological data. We also estimate that the total volume of lower crustal high-amplitude reflections within the 3D dataset may be over 2000 km 3 . 2D gravity modelling of a seismic line located along the central-northern Corona Ridge supports the interpretation of lower crustal intrusions beneath the central-northern Corona Ridge. This study provides evidence of a potential mechanism for Paleogene uplift within the region. If uplift occurred as a result of lower crustal intrusions emplaced within the crust during the Paleogene, based on previous work, we estimate that around 300 m of uplift may have been generated within the Corona Ridge area.