Crustal Structure and Composition of the Newfoundland Nonvolcanic Rifted Margin on the Future ODP Leg 210 Drilling Transect
Abstract
The Newfoundland side of the Newfoundland/Iberian conjugate margin pair is an excellent place to study continental extension and rifting. The SCREECH study area is conjugate to drilling transects and seismic data sets collected on the Iberian margin. Lingering questions concerning the symmetry of rifting processes and architecture and the lack of magmatism on nonvolcanic margins can be addressed by obtaining high-quality images of the Newfoundland margin to complete the picture. We present a preliminary velocity model and processed, time-migrated, multi-channel seismic reflection lines collected during the SCREECH survey. These lines include Transect 2, one of three primary transects collected offshore Newfoundland in July-August 2000, and a network of grid lines that cross Transect 2 at proposed drill sites for upcoming ODP leg 210 in 2003. Transect 2 extends from continental crust on the outer edge of the Grand Banks southeast across extended continental crust, "transitional" crust of unknown origin, and 60 km seaward of magnetic anomaly M0. Three major basement types are observed on Transect 2: (1) block-faulted continental crust with abundant lower-crustal and Moho reflections, (2) a 70-km-wide zone of enigmatic origin, showing relatively smooth, transparent basement beneath the "U" reflector, and (3) a wide zone characterized by significant basement topography (>1.5 km) straddling M0. The basement highs and intra-basement reflections observed on the seaward end of Transect 2 strongly resemble serpentinite ridges imaged and drilled on the Iberian margin. Crustal domain (2), however, is dissimilar from any basement type imaged on the conjugate margin. Additionally, no reflectors comparable in strength and continuity to the "S" reflector, identified as a possible decollement fault on the Iberian margin, are observed on Transect 2. One possible explanation of these asymmetries is a model that invokes a rolling hinge to exhume mantle from beneath continental crust. Other observations on Transect 2 support this assertion. A bright landward-dipping reflector located between crustal domains (1) and (2) at Moho depths might represent the rolling-hinge. Basins in crustal domain (3) appear to deepen and contain older sedimentary sequences seaward, suggesting a landward younging of the "transitional" crust. Although basement types (2) and (3) have different topographic expressions, the transition from smooth to high relief basement is gradual. These observations suggest that all basement seaward of block-faulted continental crust may be serpentinized, continental mantle exhumed from beneath North America by a fault located at the edge of the continent. This interpretation is supported by our velocity model, which shows a high velocity gradient in both crustal domains (2) and (3), with velocities increasing from 5.0 km/s to >7 km/s.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2001
- Bibcode:
- 2001AGUFM.T52C0956S
- Keywords:
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- 3025 Marine seismics (0935);
- 7200 SEISMOLOGY;
- 8105 Continental margins and sedimentary basins