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Is Alpha Ridge Oceanic or Continental Crust? Constraints from Gravity and Magnetic Potential Field Data

Nick J. Kusznir1 and Carmen Gaina2
1Earth Interior Dynamics, Liverpool University, Liverpool, United Kingdom.
2Center for Geodynamics, Geological Survey of Norway, Trondheim, Norway.

The ocean basins of the Arctic formed during the Mesozoic and Cenozoic as a series of ocean basins and rifts leading to a complex distribution of oceanic crust, thinned continental crust, micro-continents, ridges and rifted continental margins. The structure and origin of the Alpha and Mendeleev Ridges within the Amerasia Basin are contentious; possibilities include thick oceanic crust formed by ocean ridge - mantle plume interaction, micro-continents or thinned continental crust with hot-spot volcanic addition. We use gravity inversion, incorporating a lithosphere thermal gravity anomaly correction, to map Moho depth, crustal thickness and continental lithosphere thinning factor for the Amerasia Basin in order to determine the distribution of oceanic and continental lithosphere. Data used in the gravity inversion are gravity data from the NGA (U) Arctic Gravity Project, IBCAO bathymetry and sediment thickness from Laske et al. (1997). Our gravity inversion predicts thin crust (5-10 km thickness) and high continental lithosphere thinning factors in the Makarov, Podvodnikov, Nautilus and Canada Basins consistent with these basins being oceanic or highly thinned continental crust. Larger crustal thicknesses, in the range 20-30 km, are predicted for the Alpha, Mendeleev and Lomonosov Ridges. Moho depths predicted by gravity inversion compare well with estimates from the TransArctica-Arctica seismic profiles. We predict that Alpha Ridge has in its centre a crustal thickness of 25-30 km and possesses sharp angular edges. While Alpha Ridge has been compared with Iceland for structure and origin, its very large positive satellite derived MF6 total magnetic field anomaly at 350 km elevation (Maus et al. 2009) are an order of magnitude larger in amplitude and spatial extent than for Iceland suggesting a different origin. A global search shows that Kerguelen and Broken Ridge have similar 25-30 km crustal thicknesses, sharp angular edges, and large positive MF6-dt350 satellite magnetic anomalies. Evidence suggests that Kerguelen and Broken Ridge are micro-continents formed by poly-phase continental breakup (giving their angular sharp edges) with LIP volcanic addition. Our interpretation is that, by analogy, Alpha Ridge is also a micro-continent formed by poly-phase continental breakup with LIP volcanic addition.

 

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

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