Shallow and deep crustal structure of the western Sverdrup Basin, arctic Canada

摘要: An analysis of gravity data along two detailed profiles over the western Sverdrup Basin in the Canadian Arctic supports a seismic refraction model. Drill holes as deep as 5.4 km near the profiles provide excellent density control. Mean densities in the thickest part of the basin exceed those in the thinner parts by an average of 0.13 Mg/m3.Bouguer anomalies corrected for the effect of water, sedimentary, and crystalline layers indicate significant anomalies that vary in width from 20 to 275 km and in amplitude from 3 to 46 mGal (30 to 460 μm s−2). These can all be explained by density structures within the sedimentary column. Sedimentary thickness along the profiles varies from 9 to 17.4 km, crystalline thickness varies from 18 to 33 km, and the total crustal thickness varies from 34 to 42 km. The analysis also shows: (1) negative gravity effects of about 60 to 120 mGal (600 to 1200 μm s−2) due to the mass deficiency of the water and sediments are offset by positive gravity effects of similar magnitude due to crustal thinning; (2) isostatic compensation of water and sediments by a mantle antiroot is evident from a regional free-air anomaly near zero and the apparent inverse variation of sedimentary thickness with the thickness of the crystalline crust; (3) in the thickest part of the basin, undulations at the sedimentary–crystalline boundary are in phase with and smaller in amplitude than undulations at the crust–mantle boundary; conversely, in the thinnest part of the basin, these undulations are out of phase and larger in amplitude.These effects may be explained by stretching of a crystalline crust and a general decrease in crustal rigidity with depth during sediment accumulation and subsequent orogenic events.