Arctic Crustal Thickness and Oceanic-Continent Transition Structure from OCTek Gravity Inversion: Laptev, East Siberian and Chukchi Seas

Nick Kusznir

Using gravity anomaly inversion we have produced regional maps of crustal thickness and oceanic lithosphere distribution for the greater Arctic region including the Laptev, East Siberian and Chukchi Seas. Moho depth, crustal basement thickness, and continental lithosphere thinning factors have been determined for the Amerasia and Eurasia Basins and their adjacent continental margins using OCTek, a new 3D spectral gravity inversion method, which incorporates a lithosphere thermal gravity anomaly correction. The resulting crustal thickness and lithosphere thinning maps are used to determine ocean-continent transition structure and continent-ocean boundary location. Crustal cross-sections with Moho from gravity inversion are used to distinguish margin magmatic type (e.g. indentify magma-poor margins). Data used in the gravity inversion are public domain gravity, bathymetry and sediment thickness data. Moho depths predicted by gravity inversion calibrate well with seismic refraction estimates. OCTek gravity inversion predicts thin crust and high continental lithosphere thinning factors in the Eurasia, CA, Makarov and Podvodnikov Basins consistent with these basins being oceanic or, in the case of the SW Podvodnikov Basin, highly thinned continental crust. Gravity inversion predicts thin crustal basement under the Laptev Sea, of between 10-15 km thickness and covered by thick Cenozoic sediments, which is interpreted as highly thinned rifted continental crust formed as the eastward continuation of Gakkel Ridge sea-floor spreading in the Eurasia Basin. The present axis of Laptev rifting, as indicated by a clear lineation of earthquake epicentres, is located in the northern Laptev Sea adjacent to the De Long Massif, and follows earlier rifting and greater crustal thinning in the southern Laptev Sea. For the transition between the East Siberian Shelf and the Podvodnikov Basin, gravity inversion shows a sharp transition from thick continental crust to oceanic (or thinned continental). Thin continental or oceanic crust of thickness 7 km or less is predicted under the North Chukchi Basin and has major implications for understanding the Mesozoic and Cenozoic plate tectonic history of the Siberian and Chukchi Amerasia Basin margins, and the evolution of Chukchi Cap and Northwind Ridge.

AAPG Search and Discovery Article #90177©3P Arctic, Polar Petroleum Potential Conference & Exhibition, Stavanger, Norway, October 15-18, 2013