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

Abstract

We present the combined results of deep multichannel refl ection and refraction seismic surveys across the Flemish Cap-Goban Spur conjugate margin pair (North Atlantic), which we use to infer rifting style and breakup. Profi les on both margins cross magnetic anomaly 34 and extend into oceanic crust, making it possible to observe the complete history from continental rifting through to the formation of initial oceanic crust. The deep multichannel seismic (MCS) refl ection data have previously been used to support a model of symmetric pure shear extension followed by asymmetric breakup and a sharp continent-ocean boundary. Using both types of seismic data, our results indicate instead that asymmetric structures are formed during all stages of rifting, breakup, and complex transition to oceanic spreading. The differing nature of the two oceancontinent transition zones is particularly striking. For Flemish Cap, our reprocessed image of the MCS profi le clearly shows tilted fault blocks beneath back-tilted sediment packages, consistent with a wide region of highly thinned continental crust inferred from wideangle seismic data. In contrast, normal incidence and wide-angle seismic data for the Goban Spur transition zone indicate the presence of exhumed serpentinized mantle.

Kinematic Evolution of the Southern North Atlantic: Implications for the Formation of Hyperextended Rift Systems

“…The North Galicia margin rifted away from the Goban Spur margin and experienced a strike‐slip regime with the motion of the Flemish Cap. This motion is consistent with the highly asymmetric conjugate margins between Goban Spur and Flemish Cap (Gerlings et al, ). Rifting continued in the Rockall Trough until the Barremian/Aptian boundary and also between Newfoundland and Ireland where extension was first accommodated by crustal oblique deformation and later by mantle exhumation.…”

“…Only few studies are available on this area, and most of the data are from the Flemish Cap and Goban Spur conjugate margins. These margins are highly asymmetric (Gerlings et al, ). The Goban Spur shows a progressively necked crustal structure, with crust thinning from ~20 km to ~6 km over a distance of ~40 km and a zone of exhumed mantle that is up to 70 km wide (Bullock & Minshull, ).…”

3D development of detachment faulting during continental breakup

“…Subsequent slip and deformation would then result in further water influx and further mantle hydration beneath the thinning crust (Bayrakci et al, 2016;Prada et al, 2017). The development of a late stage asymmetric detachment system during the rifting is compatible with the widely observed asymmetry at conjugate magma-poor margin pairs (Gerlings et al, 2012;Reston, 2010), which is only developed when the crust is thinner than ~10 km (Reston and Pérez-Gussinyé, 2007;Reston, 2010), that is where it had become entirely brittle during rifting, allowing serpentinization.…”

Continental hyperextension, mantle exhumation, and thin oceanic crust at the continent‐ocean transition, West Iberia: New insights from wide‐angle seismic

“…The required half‐spreading rate is 7.4 mm/yr, classifying the spreading here as ultraslow, which is consistent with the observed mantle exhumation and onset of thin oceanic crust. South of the Deep Galicia margin, at the southern Iberia Abyssal Plain, the formation of oceanic crust 6–7 km thick is interpreted to have begun at 127–125 Ma, while north of the Deep Galicia margin, at the Goban Spur, a final breakup age of 100 Ma is proposed [ Gerlings et al ., ; Minshull et al ., ]. These breakup dates, decreasing in age from south to north, are consistent with the observation of a northward propagating rift margin [ Masson and Miles , ].…”