The deep crustal structure beneath the North Sea is poorly understood since it is constrained by only a few seismic reflection and refraction profiles. However, it is widely acknowledged that the mid to lower crust plays important roles in rift initiation and evolution, particularly when large-scale sutures and/or terrane boundaries are present, since these inherited features can focus strain or act as inhibitors to extensional deformation. Ancient tectonic features are known to exist beneath the iconic failed rift system of the North Sea, making it an ideal location to investigate the complex interplay between pre-existing regional heterogeneity and rifting. To this end, we produce a 3-D shear wave velocity model from transdimensional ambient seismic noise tomography to constrain crustal properties to ∼30 km depth beneath the North Sea and its surrounding landmasses. Major North Sea sedimentary basins appear as low shear wave velocity zones that are a good match to published sediment thickness maps. We constrain relatively thin crust (13–18 km) beneath the Central Graben depocentres that contrasts with crust elsewhere at least 25–30 km thick. Significant variations in crustal structure and rift symmetry are identified along the failed rift system that appears to be related to the locations of Laurentia–Avalonia–Baltica palaeoplate boundaries. We constrain first-order differences in structure between palaeoplates; with strong lateral gradients in crustal velocity related to Laurentia–Avalonia–Baltica plate juxtaposition and reduced lower crustal velocities in the vicinity of the Thor suture, possibly representing the remnants of a Caledonian accretionary complex. Our results provide fresh insight into the pivotal roles that ancient terranes can play in the formation and failure of continental rifts and may help explain the characteristics of other similar continental rifts globally.
The work contained in this paper was conducted during a PhD study undertaken as partcof the Natural Environment Research Council (NERC) Centre for Doctoral Training (CDT) incGeophysical Journal International Oil & Gas [grant number NEM00578X/1]. This work was performed using the Maxwell HighcPerformance Computing Cluster of the University of Aberdeen IT Service (www.abdn.ac.uk/staffnet/research/hpc.php), provided by Dell Inc. and supported by AlcescSoftware. Plots were generated with the Generic Mapping Tools or GMT (Wessel et al., 2013).cWe thank Nick Schofield and Tim Pharaoh for constructive conversations, which aided thecinterpretation of our results, and Amy Gilligan for her insightful advice during preparation ofcthis manuscript. We also thank Richard England and an anonymous reviewer for theirccomments on the original version of the manuscript.
- Seismic tomography
- Seismic noise
- Continental tectonics: extensional
- Crustal structure
- Continental tectonics