D. Chian et al., Crustal structure beneath Orphan Basin and implications for nonvolcanic continental rifting, J GEO R-SOL, 106(B6), 2001, pp. 10923-10940
A wide-angle seismic profile was acquired across the northeast Newfoundland
margin, seaward to Orphan Knell. The profile is complemented by existing m
ultichannel reflection data, two online deep wells, and other deep seismic
reflection and refraction lines. Modeling of data from 15 ocean bott om sei
smometers provides the seismic velocity structure for a significant portion
of the similar to 400-km-wide stretched continental crust on this margin.
Prerift metasedimentary rocks have a topographic relief of up to 5 km, with
a velocity of similar to5.2 km/s increasing to 5.9 km/s. Unaltered crystal
line crust below the metasedimentary section has a velocity range of 6.1-6.
5 km/s. Most of the lower crust landward of Orphan Knell has a typical cont
inental lower crustal velocity (6.8-7.0 km/s), and the lower crust shallows
significantly beneath Orphan Knell. Our model shows no evidence for the 5-
km-thick, 7.35 km/s layer modeled from data of an earlier experiment and in
terpreted as magmatic underplating but instead indicates that thinned conti
nental crust extends seaward for 360 km without underplating, implying nonv
olcanic rifting for the NE Newfoundland margin. We suggest that continental
stretching persisted from similar to 180 Ma to Chron 34N time (similar to
101 Ma) when the final breakup between Canada and western Europe took place
, leaving a 400-kmwide zone of thinned continental crust underneath the she
lf and deep water area of the Orphan Basin. On the landward side of the bas
in, gravity modeling indicates a zone of very thin (6-8 km) crust, possibly
a failed rift center formed as a result of the northward progression of no
nvolcanic rifting between Canada and Europe. A possible sub-Moho reflector
suggests generally uniform stretching of the crust and upper mantle, and th
e absence of volcanics and underplating is in contrast to the observations
on related rift basins of the Grand Banks.