Continental breakup and the onset of ultraslow seafloor spreading off Flemish Cap on the Newfoundland rifted margin

Abstract

Prestack depth-migrated seismic reflection data collected off Flemish Cap on the Newfoundland margin show a structure of abruptly thinning continental crust that leads into an oceanic accretion system. Within continental crust, there is no clear evidence for detachment surfaces analogous to the S reflection off the conjugate Galicia Bank margin, demonstrating a first-order asymmetry in final rift development. Anomalously thin (3-4 km), magmatically produced oceanic crust abuts very thin continental crust and is highly tectonized. This indicates that initial accretion of the oceanic crust was in a magma-limited setting similar to presentday ultraslow spreading environments. Seaward, oceanic crust thins to Ͻ1.3 km and exhibits an unusual, highly reflective layering. We propose that a period of magma starvation led to exhumation of mantle in an oceanic core complex that was subsequently buried by deep-marine sheet flows to form this layering. Subsequent seafloor spreading formed normal, ϳ6-km-thick oceanic crust. This interpretation implies large fluctuations in the available melt supply during the early stages of seafloor spreading before a more typical slow-spreading system was established.

Lithospheric extension from rifting to continental breakup at magma-poor margins: rheology, serpentinisation and symmetry

“…Within this unit the velocity increases downwards from about 7 km/s (<25% serpentinisation) to typical unserpentinised mantle velocities (8 km/s) over a thickness of about 6 km, consistent with the modelling results of Pé rez-Gussinyé and . The landward limit of the serpentinites occurs where the crust is about 8 km thick, consistent with the complete embrittlement of the crust; Hopper et al (2004) report the presence of possible faults cutting down through the entire crust, but no east-cutting ''Z reflection'' on the Flemish Cap margin forming a mirror image to S off Galicia. The most obvious place to interpret a detachment at this margin (Fig.…”

Rifts and Rifted Margins: A Review of Geodynamic Processes and Natural Hazards

“…Offshore Iberia for example, the width of the highly thinned crustal region amounts to about 70 km [Whitmarsh et al, 2001] while the conjugate margin of Newfoundland exhibits only about 20 km of hyperextended crust [Hopper et al, 2004]. In the central South Atlantic, the asymmetry is even larger: up to 200 km offshore Angola [Contrucci et al, 2004], and about 30 km at the conjugate Brazilian margin .…”

“…They also feature wide areas of highly thinned, so-called hyperextended crust with a thickness of less than 10 km, where crust and mantle deformation appears to be tightly coupled Mohn et al, 2014]. Well-studied examples of magma-poor margins comprise the Iberia-Newfoundland conjugates [Hopper et al, 2004;Reston, 2007;Ranero and Perez-Gussinye, 2010;Sutra and Manatschal, 2012], the Central South Atlantic segment [Contrucci et al, 2004;Aslanian et al, 2009;Mohriak and Leroy, 2012], the Australian North West Shelf [Karner and Driscoll, 1999], the eastern Gulf of Aden and the South China Sea [Zhou and Yao, 2009;Franke, 2013].…”

The time scales of continental rifting: Implications for global processes

“…Where magma is absent until the onset of seafl oor spreading, rift segments widen to as much as 5 times their original widths, drastically reducing plate strength (e.g., Hopper et al, 2004;Reston and Pérez-Gussinyé, 2007;Lizarralde et al, 2007;Péron-Pinvidic and Manatschal, 2010;van Avendonk et al, 2009). The presence of magma during rifting decreases the amount of stretching required to achieve plate rupture, as can be seen in the much narrower widths of conjugate magmatic margins worldwide (e.g., Coffi n and Eldholm, 1994; Menzies et al, 2002;Shillington et al, 2009;Leroy et al, 2010).…”