Crustal structure of a nonvolcanic rifted margin east of Newfoundland

Abstract

A detailed seismic refraction study was undertaken of the rifted continental margin southeast of the Grand Banks of Newfoundland, along a preexisting deep multichannel seismic reflection profile. The primary objectives were to determine the topography of Moho across the margin, to detect any evidence for crustal underplating, and to determine the position of the continent‐ocean boundary. Data were obtained from nine ocean bottom seismometers deployed along the profile, with an array of six 1000‐inch3 air guns as the source. Two additional refraction lines were shot parallel to structure over the continental slope. The resultant velocity model is well constrained and consistent with the observed gravity. The crust thins abruptly beneath the continental slope to a major structural transition identified as the continent‐ocean boundary. There is no significant magmatic underplating of the thinned continental crust. Seaward of the transition, the seismic velocity structure is characterized by a 50‐km‐wide zone of intermediate velocity (7.2–7.6 km/s). Beyond this is a thin (3–5 km) crust with low velocity (4.5–5 km/s) and high gradient, over mantle with a velocity of 7.7 km/s increasing to 8.0 km/s. The zone of intermediate velocity is interpreted to be highly serpentinized mantle material beneath a very thin crust, suggesting little or no magmatic activity during and immediately after rifting. This interpretation is consistent with results from adjacent and conjugate margins.

Constraints on Moho Depth and Crustal Thickness in the Liguro-Provençal Basin from a 3d Gravity Inversion : Geodynamic Implications

“…Thin crust overlying a high velocity layer is found on the western margin of Iberia (3-4 km thick above a 7.3 to 7.6 km/s layer, Whitmarsh et al, 1990;Whitmarsh et al, 1993), in the Tagus abyssal Plain (2 km thick above 7.6 km/s layer increasing to 7.9 km/s towards Moho, Pinheiro et al, 1992) and its conjugate Newfoundland margin off Grand Banks (2-3 km thick above 7.2 to 7.7 km/s layer, Reid, 1994), accross Southwest Greenland margin (2.5 km thick above 7.0 to 7.6 km/s layer, Chian and Louden, 1994) and its conjugate Labrador margin (1-2 km thick above a 6.4 to 7.7 km/s layer, Chian et al, 1995) On the southern Newfoundland margin the high velocity body is limited by one or two landward dipping reflectors rising to basement surface seaward and connecting to Moho landward (Keen and de Voogd, 1988;Reid, 1994). The similarity with the T reflector of the Gulf of Lion is striking.…”

Crustal structure of northern Baffin Bay: Seismic refraction results and tectonic implications

“…For these reasons, we suggest that this margin may be amagmatic, analogous to those of the Labrador Sea [Chian et al, 1995] and the Grand Banks [Reid, 1994], and that the 6.8-km/s layer may in fact be serpentinized mantle. If this interpretation is correct, it implies that the rifting in northern Baffin Bay took place, at least initially, with little or no melt production, and that the thick sedimentary sequences south of the paleoshelf edge in fact directly overlies tectonically exposed mantle.…”

Rheological evolution during extension at nonvolcanic rifted margins: Onset of serpentinization and development of detachments leading to continental breakup

“…As thinning progresses, the thin continental crust gives way to the continent-ocean transition (COT) characterized by basement typical of neither oceanic nor continental crust. In several cases this region has been interpreted as an expanse of serpentinized peridotite (e.g., Labrador Sea [Chian et al, 1995]; Newfoundland [Reid, 1994] [Boillot et al, 1989;Chian et al, 1999].…”