A deep seismic investigation of the Flemish Cap margin: implications for the origin of deep reflectivity and evidence for asymmetric break-up between Newfoundland and Iberia

Abstract

SUMMARY Seismic reflection and refraction data were acquired along the southeast margin of Flemish Cap at a position conjugate to drilling and geophysical surveys across the Galicia Bank margin. The data document first‐order asymmetry during final break‐up between Newfoundland and Iberia. An abrupt necking profile of continental crust observed off Flemish Cap contrasts strongly with gradual tapering on the conjugate margin. There is no evidence beneath Flemish Cap for a final phase of continental extension that resulted in thin continental crust underlain by a strong ‘S’‐like reflection, which indicates that this mode of extension occurred only on the Galicia Bank margin. Compelling evidence for a broad zone of exhumed mantle or for peridotite ridges is also lacking along the Flemish Cap margin. Instead, anomalously thin, 3–4‐km‐thick oceanic crust is observed. This crust is highly tectonized and broken up by high‐angle normal faulting. The thin crust and rift structures that resemble the abandoned spreading centre in the Labrador sea suggest that initial seafloor spreading was affected by processes observed in present‐day ultra‐slow spreading environments. Landwards, Flemish Cap is underlain by a highly reflective lower crust. The reflectivity most likely originates from older Palaeozoic orogenic structures that are unrelated to extension and break‐up tectonics.

Structure of the Flemish Cap margin, Newfoundland: insights into mantle and crustal processes during continental breakup

“…4). Large, sediment-filled rift basins are absent in the reflection images and the wide-angle data show no evidence for sediment cover (see Funck et al 2003;Hopper et al 2006). The basement has uniform P-wave velocities between 6.0 and 6.7 km s 21 , consistent with that typical of Appalachian continental crust.…”

“…The SCREECH survey (Studies of Continental Rifting and Extension off the Eastern Canadian sHelf) was conducted in 2000 to better understand the large-scale structure of the Newfoundland margin at positions conjugate to the major geophysical surveys and drilling transects off the Iberian margin (Funck et al 2003;Hopper et al 2004Hopper et al , 2006Lau et al 2006a, b;Shillington et al 2004Shillington et al , 2006. Multichannel seismic reflection and wide-angle seismic refraction data were acquired along three primary transects.…”

“…The data shown are published in Funck et al (2003) and Hopper et al (2004Hopper et al ( , 2006. We do not attempt to replicate all of those results here, but focus on key summary figures and portions of the data set that are particularly relevant for the numerical modelling exercises described in this volume.…”

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

“…Outboard, Flemish Cap thins more abruptly than Goban Spur, with upper and middle crustal densities pinching out more rapidly than on the Irish margin. The lack of faulting observed on Flemish Cap (Funck et al 2003;Hopper et al 2006), and the broad area of faulting leading to the development of a set of elongate basins and highs documented for the Goban Spur Naylor & Shannon 2009), may have provided a more distributed zone to accommodate thinning on the Irish margin. Moho depth and gravity anomaly at magnetic chron 34 match very well along this transect (Fig.…”

“…NE-SW extension, starting in the Late Cretaceous Tucholke et al 1989;Hopper et al 2006;Tucholke & Sibuet 2007), separated the NE margins of Flemish Cap and Orphan Basin from the Goban Spur and the Porcupine High, offshore Ireland. This was interpreted by Doré et al (1999) as an oblique reopening of the Caledonian-Appalachian suture and fold system.…”