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

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Lau, K. W. Helen
Louden, Keith E.
Funck, Thomas
Tucholke, Brian E.
Holbrook, W. Steven
Hopper, John R.
Larsen, Hans Christian
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Continental margins
Crustal structures
Refraction seismology
Rifted margins
A P-wave velocity model along a 565-km-long profile across the Grand Banks/Newfoundland basin rifted margin is presented. Continental crust ~36-kmthick beneath the Grand Banks is divided into upper (5.8-6.25 km/s), middle (6.3- 6.53 km/s) and lower crust (6.77-6.9 km/s), 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 in upper layer; ~5 km/s in lower layer). Abrupt crustal thinning (Moho dip ~ 35º) 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 seaward until they are completely removed, while very thin (<3 km) upper crust continues ~60 km farther seaward. 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-kmwide zone with reduced mantle velocities (7.6-7.9 km/s) is observed, which is interpreted as partially (<10%) serpentinized mantle. Seaward of the transitional basement, 2- to 6-km-thick crust with layer 2 (4.5-6.3 km/s) and layer 3 (6.3-7.2 km/s) 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.
Author Posting. © Blackwell, 2006. This is the author's version of the work. It is posted here by permission of Blackwell for personal use, not for redistribution. The definitive version was published in Geophysical Journal International 167 (2006): 127-156, doi:10.1111/j.1365-246X.2006.02988.x.
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