Funck
Thomas
Funck
Thomas
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ArticleA 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(Blackwell Publishing, 2006-02-21) Hopper, John R. ; Funck, Thomas ; Tucholke, Brian E. ; Louden, Keith E. ; Holbrook, W. Steven ; Larsen, Hans ChristianSeismic 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.
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PreprintCrustal structure across the Grand Banks–Newfoundland Basin Continental Margin – I. Results from a seismic refraction profile( 2006-03-03) Lau, K. W. Helen ; Louden, Keith E. ; Funck, Thomas ; Tucholke, Brian E. ; Holbrook, W. Steven ; Hopper, John R. ; Larsen, Hans ChristianA 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.
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ArticleCrustal structure of the ocean-continent transition at Flemish Cap : seismic refraction results(American Geophysical Union, 2003-11-19) Funck, Thomas ; Hopper, John R. ; Larsen, Hans Christian ; Louden, Keith E. ; Tucholke, Brian E. ; Holbrook, W. StevenWe conducted a seismic refraction experiment across Flemish Cap and into the deep basin east of Newfoundland, Canada, and developed a velocity model for the crust and mantle from forward and inverse modeling of data from 25 ocean bottom seismometers and dense air gun shots. The continental crust at Flemish Cap is 30 km thick and is divided into three layers with P wave velocities of 6.0–6.7 km/s. Across the southeast Flemish Cap margin, the continental crust thins over a 90-km-wide zone to only 1.2 km. The ocean-continent boundary is near the base of Flemish Cap and is marked by a fault between thinned continental crust and 3-km-thick crust with velocities of 4.7–7.0 km/s interpreted as crust from magma-starved oceanic accretion. This thin crust continues seaward for 55 km and thins locally to ~1.5 km. Below a sediment cover (1.9–3.1 km/s), oceanic layer 2 (4.7–4.9 km/s) is ~1.5 km thick, while layer 3 (6.9 km/s) seems to disappear in the thinnest segment of the oceanic crust. At the seawardmost end of the line the crust thickens to ~6 km. Mantle with velocities of 7.6–8.0 km/s underlies both the thin continental and thin oceanic crust in an 80-km-wide zone. A gradual downward increase to normal mantle velocities is interpreted to reflect decreasing degree of serpentinization with depth. Normal mantle velocities of 8.0 km/s are observed ~6 km below basement. There are major differences compared to the conjugate Galicia Bank margin, which has a wide zone of extended continental crust, more faulting, and prominent detachment faults. Crust formed by seafloor spreading appears symmetric, however, with 30-km-wide zones of oceanic crust accreted on both margins beginning about 4.5 m.y. before formation of magnetic anomaly M0 (~118 Ma).