Crustal structure across the Grand Banks-Newfoundland Basin Continental Margin - I. Results from a seismic refraction profile

• Published in: Geophysical Journal International
• Main Authors: Lau, K. W.Helen, Louden, Keith E., Funck, Thomas, Tucholke, Brian E., Holbrook, W. Steven, Hopper, John R., Christian Larsen, Hans
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2006
• Subjects: Continental margins; Crustal structures; Refraction seismology; Rifted margins; Newfoundland
• Online Access: https://curis.ku.dk/portal/da/publications/crustal-structure-across-the-grand-banksnewfoundland-basin-continental-margin--i-results-from-a-seismic-refraction-profile(817454ce-a364-430d-afe3-6b467edf940a).html; https://doi.org/10.1111/j.1365-246X.2006.02988.x; http://www.scopus.com/inward/record.url?scp=33749420405&partnerID=8YFLogxK

A P-wave velocity model along a 565-km-long profile across the Grand Banks-Newfoundland Basin rifted margin is presented. Continental crust ∼36 km thick beneath the Grand Banks is divided into upper (5.8-6.25 km s -1 ), middle (6.3-6.53 km s -1 ) and lower crust (6.77-6.9 km s -1 ), consistent with velocity structure of Avalon zone Appalachian crust. Syn-rift sediment sequences 6-7 km thick occur in two primary layers within the Jeanne d'Arc and the Carson basins (∼3 km s -1 in upper layer; ∼5 km s -1 in lower layer). Abrupt crustal thinning (Moho dip ∼35°) beneath the Carson basin and more gradual thinning seaward forms a 170-km-wide zone of rifted continental crust. Within this zone, lower and middle continental crust thin preferentially seawards until they are completely removed, while very thin (<3 km) upper crust continues ∼60 km farther seawards. Adjacent to the continental crust, high-velocity gradients (0.5-1.5 s -1 ) define an 80-km-wide zone of transitional basement that can be interpreted as exhumed, serpentinized mantle or anomalously thin oceanic crust, based on its velocity model alone. We prefer the exhumed-mantle interpretation after considering the non-reflective character of the basement and the low amplitude of associated magnetic anomalies, which are atypical of oceanic crust. Beneath both the transitional basement and thin (<6 km) continental crust, a 200-km-wide zone with reduced mantle velocities (7.6-7.9 km s -1 ) is observed, which is interpreted as partially (<10 per cent) serpentinized mantle. Seawards of the transitional basement, 2- to 6-km-thick crust with layer 2 (4.5-6.3 km s -1 ) and layer 3 (6.3-7.2 km s -1 ) velocities is interpreted as oceanic crust. Comparison of our crustal model with profile IAM-9 across the Iberia Abyssal Plain on the conjugate Iberia margin suggests asymmetrical continental breakup in which a wider zone of extended continental crust has been left on the Newfoundland side.