Seismic structure of the Hatton–Rockall area: an integrated seismic/modelling study from composite datasets

Abstract

During 1987-9 the United Kingdom Department of Energy recorded coincident seismic reflection, sonobuoy wide-angle reflection and refraction, and expanding spread refraction data across the Hatton-Rockall Plateau, lying within the continental margin to the west of Scotland. Some 780 km of deep multichannel seismic reflection data were used to define and control the structural model. The presence of Tertiary basalts throughout the area gives rise to severe attenuation of incident energy and substantial velocity inhomogeneities. Information from 53 sonobuoys and 5 reversed expanding spread profiles recorded along the lines allow independent determination of velocity structure. An integrated model is constructed layer by layer from the surface down to Moho. Using information gained from these integrated datasets, the velocity-depth structure of the area can be determined across the entire margin and imaging at depth beneath the basalts substantially improved. Deep, upper mantle reflections are clearly seen beneath Rockall Bank. Evidence of probable Tertiary inversion is seen in Hatton Basin. The main structure of Hatton Bank is fault controlled, and both highly tilted fault blocks and oceanward-dipping reflector sequences are observed. The presence of a two-layer continental crust is revealed, thinned within Rockall Trough and deepening to the east beneath the Hebridean Platform and the west below Hatton-Rockall Plateau.The Hatton-Rockall area is located within the continental The Rockall and Hatton Bank passive continental margins margin to the west of Scotland (Fig. 1). Rockall Trough is a have been studied by a number of workers (e.g. Scrutton 1972; deep bathymetric depression lying between the British main- Bott et al. 1979;Roberts et al. 1981Roberts et al. , 1988; Joppen and White land and Rockall Plateau, which consists of Rockall Bank, 1990) but the structure, history, and evolution of the area have Hatton-Rockall Basin and Hatton Bank. remained enigmatic. Seismic data in the area are sparse and Fig. 1. Continental margin west of Britain. The solid line represents common-depth point tracks. Bathymetry in metres and major physiographic features are shown.

A refraction seismic transect from the Faroe Islands to the Hatton‐Rockall Basin

“…Lower crustal velocities of 6.6 km/s north of George Bligh Bank (Figures 10 and 11) are compatible with other data from Lewisian basement on the Hebrides shelf [ Klingelhöfer et al , 2005; Keser Neish , 1993]. According to the compilation of Holbrook et al [1992], these lower crustal velocities fall within the range of mafic granulite.…”

“…Figure 17 compares the results from line B with other deep‐crustal seismic data from the Hatton‐Rockall Basin, including line 87–3 [ Keser Neish , 1993], iSIMM line 5 [ White et al , 2008], and RAPIDS line 13 [ Vogt et al , 1998] (for location, see Figure 1). The Moho depth on all four lines varies between 17 and 20 km and the velocities in the two upper crustal layers on line 87–3 and our line B are very similar (5.6 to 5.8 km/s in the upper layer and 6.5 km/s underneath).…”

“…Solid lines indicate layer boundaries; dashed lines represent velocity contours. Profiles are taken from line 87–3 [ Keser Neish , 1993], iSIMM line 5 [ White et al , 2008], line B (Figure 11), RAPIDS line 13 [ Vogt et al , 1998], and line BANS‐1 [ Klingelhöfer et al , 2005]. For location of these lines, see Figure 1.…”

“…Red solid lines show the location of the two refraction seismic profiles of this study. Dashed lines show the location of other seismic experiments that are discussed in the text: lines AMP‐D, AMP‐E, and BANS‐1 [ Klingelhöfer et al , 2005]; iSIMM line 5 [ Smith et al , 2005; White et al , 2008]; lines 87–3 [ Keser Neish , 1993]; and RAPIDS lines 21, 13, and 14 [ Vogt et al , 1998]. Filled circles indicate the location of DSDP wells at sites 116 and 117 [ Laughton et al , 1972].…”

Brittle tectonic reconstruction of palaeo-extension inherited from Mesozoic rifting in West Zagros (Kermanshah, Iran)

“…The Rockall Trough is a c. 200 km wide basin separating the British continental shelf from the Rockall Plateau with a maximum depth of c. 3 km (see England & Hobbs 1997). There is no evidence for oceanic crust within the trough so that wideangle refraction seismic experiments demonstrated that the centre of trough is floored by highly stretched continental crust with a thickness of c. 5.7 km (Roberts et al 1988;Joppen & White 1990;Keser Neish 1993;Hauser et al 1995). The Rockall Trough indicates an almost complete record of subsidence of the continental margin over a protracted period of time.…”