Using Gravity Data to Constrain the Nature of the Crust Beneath Baffin Bay
Abstract
The nature of the crystalline basement beneath Baffin Bay, which is covered with over 10 km of sediments in places, remains under debate. Particularly under question is whether it is composed of continental or oceanic crust or both. To the south within the Labrador Sea, seafloor spreading is confirmed to have begun some time between 86 and 61 Ma and ceased around roughly 55 Ma, as determined by well-defined magnetic lineations produced by geomagnetic reversals during spreading, as well as by samples from an ODP hole. In Baffin Bay, rift structures and volcanic materials are found close to the coast both onshore and offshore, indicating that the extensional effects of the Labrador Sea opening continued north to the Bay. Early single- line magnetic profiles collected in sparse locations suggested seafloor spreading patterns, but more recent data filling gaps between these profiles and covering most of Baffin Bay do not resemble seafloor spreading anomalies. Nonetheless, other evidence suggesting Baffin Bay is underlain by ocean crust includes seismic velocities determined by refraction studies (which in some parts of the Bay are near ~5-6 m/s, similar to oceanic layers 2 and 3) and tectonic considerations. However, other tectonic models based on reflection data, including unconformities extending offshore that represent early Cretaceous and Miocene deposition, suggest that seafloor spreading at the time of the Labrador opening could not have occurred. Drill holes have not penetrated basement beyond a few kilometers offshore and are thus not diagnostic. The recent compilation and release of gravity data through the Arctic Gravity Project (ArcGP) provides excellent coverage of Baffin Bay, the Labrador Sea, and surrounding sections of Greenland and Canada. These data allow an investigation into the suite of crustal density and thickness combinations possible within this region. We constrain regional models using onshore and offshore seismic reflection, refraction and large-scale tomography experiments, as well as available constraints on sediment density and layer thickness. Preliminary models suggest that if the crust beneath Baffin Bay is continental, it must be unusually thin, whereas if it is oceanic, its thickness falls within ranges observed over several mid-ocean ridge systems.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMGP43B0805S
- Keywords:
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- 1219 Gravity anomalies and Earth structure (0920;
- 7205;
- 7240);
- 3000 MARINE GEOLOGY AND GEOPHYSICS;
- 3040 Plate tectonics (8150;
- 8155;
- 8157;
- 8158);
- 8109 Continental tectonics: extensional (0905);
- 8157 Plate motions: past (3040)