Extensional tectonics and crustal structure: deep seismic reflection data from the northern North Sea Viking graben

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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Deep crustal structure beneath a rifted basin: results from seismic refraction measurements across the Jeanne d'Arc Basin, offshore eastern Canada

Canadian Journal of Earth Sciences ◽

10.1139/e90-155 ◽

1990 ◽

Vol 27 (11) ◽

pp. 1462-1471 ◽

Cited By ~ 19

Author(s):

I. D. Reid ◽

C. E. Keen

Keyword(s):

Crustal Structure ◽

Lower Crust ◽

Seismic Reflection ◽

Seismic Refraction ◽

Eastern Canada ◽

Seismic Reflection Data ◽

Deep Seismic Reflection ◽

Jeanne D'arc Basin ◽

Reflection Data ◽

Jeanne D'arc

A crustal seismic refraction experiment was conducted across the south Jeanne d'Arc Basin, one of the rifted sedimentary basins on the Grand Banks, offshore eastern Canada, that developed in Mesozoic time in response to extension and rifting between the North American plate and the African, Iberian, and European plates. The primary objective of this experiment, which was carried out to correlate with an existing deep seismic reflection profile, was to delineate the deep crustal geometry below the basin. Ten ocean-bottom seismometers were deployed across the basin and recorded signals from a large air-gun array. The results show that the crust is primarily composed of two layers, with velocities of 5.8–6.1 and 7.2 km/s, respectively. There is very little relief on the Moho across the basin, with only a 2 km step, from a depth of 37 to 35 km, occurring west of the basin. There is, however, considerable complexity of crustal structure, particularly near Moho depths. These results are valuable when used in conjunction with other data in the region, in particular gravity and deep seismic reflection data. The seismic reflection and refraction data sets together give a fairly complete picture of crustal geometry in the crust. The flat Moho below the basin is compatible with the detachment of the major basin-bounding fault in the lower crust or at the Moho, as seen on the reflection data. The 7.2 km/s layer is not restricted to the zone of Mesozoic crustal extension below the basin, but occurs also below relatively unextended parts of the crust. This layer may represent basaltic intrusion or underplating during a rifting event. It may also correspond to the reflective lower crust observed on the deep seismic reflection data. These results provide strong constraints on models describing the origin and evolution of this and other rifted basins.

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