Crustal structure of the Goban Spur continental margin, Northeast Atlantic, from deep seismic reflection profiling

Abstract

Deep reflection data across the UK continental margin are used to test theories concerning the origin of a pervasive reflective fabric in the lower continental crust seen on many deep reflection profiles worldwide. The origin of the reflections is at present little understood, but clearly represents an important crustal process. The Western Approaches Margin (WAM) line was designed to determine the behaviour of the lower crustal reflections in crust which has undergone significant extension. The WAM profile across the continental shelf is characterized by bright, continuous lower crustal reflections, some of which reach 30 km in length and have minimum reflection coefficients of 0.1. Deep water multiples in the area of the continental slope partially obscure reflections from the lower crust, but detailed analyses show that reflectors are present in the lower crust on the continental slope. Adjacent to the continent-ocean boundary, the lower crust on the WAM profile is well-imaged and free of noise and multiples. This very thin crust exhibits the same reflectivity pattern as is observed on the continental shelf, i.e. the upper half of the crust is blank and the lower half contains sub-horizontal reflections. The lower crustal reflections adjacent to the continent-ocean boundary are less continuous than the reflections seen on the shelf, and are interpreted as being the remnants after extension of the lower crustal reflectors observed on the continental shelf. The lower crustal reflectors are thus interpreted to pre-date the extensional episode that led to the opening of the Atlantic. The preservation of thinned sections of both transparent upper crust and reflective lower crust adjacent to the continent-ocean boundary suggests that extension by pure shear was the mechanism by which the crust was thinned in the Goban Spur area.

Flemish Cap-Goban Spur conjugate margins: New evidence of asymmetry

“…The crust at the Flemish Cap margin thins rapidly from 32 km to 6 km over a distance of only 40 km (Gerlings et al, 2011). In comparison, the Goban Spur margin thins from 28 km to 6 km over a distance of ~80 km (Horsefi eld et al, 1994;Peddy et al, 1989). Thus the Flemish Cap margin displays a sharper necking profi le than that of the Goban Spur margin, indicating asymmetry during rifting.…”

“…The crustal structure across Goban Spur was determined along a 640-km-long MCS profi le, the Western Approaches Margin (WAM; Peddy et al, 1989;Figs. 1 and 3).…”

Comparison of lithosphere structure across the Orphan Basin–Flemish Cap and Irish Atlantic conjugate continental margins from constrained 3D gravity inversions

“…2), these basins appear to have formed through differential stretching of the crust, and exhumation of serpentinized mantle has been interpreted beneath both basins O'Reilly et al 1996O'Reilly et al , 2006Reston et al 2004). Although a few studies have attempted to compare and connect these and other structures and basins from the Irish margin across to the conjugate Newfoundland margin (Sinclair et al 1994;Shannon et al 1995), the main focus of previous bridging studies has been on the Goban Spur and its conjugate margin of Flemish Cap Peddy et al 1989;Horsefield et al 1994;Bullock & Minshull 2005).…”

“…The Goban Spur margin has been investigated using both seismic reflection (Peddy & Hobbs 1987;Peddy et al 1989) and seismic refraction (Horsefield et al 1994;Bullock & Minshull 2005) surveys. Despite differing interpretations from coincident datasets, the latest and best constrained seismic refraction modelling efforts from Bullock & Minshull (2005;labelled BM05 in Fig.…”

Moho and lower crustal reflectivity beneath a young rift basin: results from a two-ship, wide-aperture seismic-reflection experiment in the Valencia Trough (western Mediterranean)

“…Matthews & Cheadle 1986; Meissner & Kusznir 1987; Matthews & Smith 1987;Reston 1988). However, if the reflectors in the Valencia Trough were produced in some way by extension, we would expect, following the arguments of Peddy et al (1989), the intensity of the reflectors to increase towards the trough axis. This clearly is not the case here, and so we believe that it is probable that the reflective layering was present prior to the Late Oligocene/Early Miocene stretching event (see Watts et al 1990, for a fuller discussion of this point).…”