Regional Gravity Models Constrain the Nature of the Crust beneath Baffin Bay

Anjana K. Shah, Chris Schenk, and Rick Saltus
USGS, Denver, CO.

Baffin Bay underwent extension for ~30 m.y. during the late Cretaceous and Paleocene, but it remains difficult to constrain whether or not this extension led to ocean floor formation because the crystalline basement is buried beneath several kilometers of sediment in most places. The release of gravity data grids by the Arctic Gravity Project and the Geologic Survey of Canada provides coverage over the entire width of Baffin Bay as well as parts of western Greenland and eastern Canada, allowing studies at scales that include onshore constraints. Here we combine these gravity data with previous teleseismic receiver function analyses to extrapolate Moho depth and thus constrain the thickness and composition of the crust beneath Baffin Bay. The resulting thickness estimates for oceanic vs. continental crust can then be compared to those observed elsewhere in order to evaluate their plausibility.

The gravity data indicate significant crustal thinning beneath Baffin Bay. Teleseismic analyses indicate Moho depths of ~37-38 km along the western shore of Greenland. Models that assume densities typical of young ocean crust predict that the igneous crust is 16-26 km thick (depending on crust and sediment densities). These estimates are very large compared to global compilations of ocean crust thickness and resemble only those which are heavily influenced by hot spot activity. However, Baffin Bay shows little evidence of plume influence. In addition, these crustal thickness estimates differ significantly from those constrained by seagoing seismic refraction experiments. Models that assume densities within ranges observed within continents yield crustal thicknesses of 14-25 km for the crystalline component. This range overlaps crustal thickness estimates for some other rifted areas, but the width of crustal thinning at Baffin Bay, ~250-400 km, is much greater. The model predictions also differ from seismic refraction results, although the emplacement of intrusive rocks with very high, mantle-like velocities within the shallow- to mid-crust might provide reconciliation. Lastly, we consider models with serpentinite residing beneath either thin oceanic crust or the sedimentary cover, as suggested by some refraction experiments. These models yield thinner crust, but require extensive amounts of serpentinite in order to match the gravity data. While none of these models matches classic examples of extensional environments, it seems unlikely that the crust beneath Baffin Bay is oceanic. Furthermore, substantial crustal thinning should indicate high levels of tectonic deformation and possibly serpentinite formation.

AAPG Search and Discovery Article #90130©2011 3P Arctic, The Polar Petroleum Potential Conference & Exhibition, Halifax, Nova Scotia, Canada, 30 August-2 September, 2011.