Gravity-inferred crustal thickness of Greenland

Abstract

Greenland's crust contains clues for understanding the dynamics of the Earth's second largest ice-sheet, as well as the Iceland hotspot over the past 100 Ma. However, our knowledge of the sub-ice crust is very limited due to the paucity of outcrops and seismic observations, particularly in central Greenland. In order to augment these sparse constraints, we modeled terrain and airborne free-air gravity data which provide estimates for Moho and related crustal thickness. These estimates were obtained from the inversion of isostatically corrected terrain effects where the computed gravity effects of the terrain's rock, water, and ice components were subtracted from the terrain-correlated free-air anomalies. The terrain-correlated free-air components were estimated from the correlation spectrum between the free-air anomalies and the terrain's gravity effects which are assumed to reflect isostatic disturbances of the crustal terrain. The results indicated an average crustal thickness of about 37 km for Greenland, with greater values by 5–10 km, in the southern Greenland Archean blocks and Caledonian Foldbelt, and comparably lower values in northern Greenland. The thinner crustal thickness estimates in the north are strongly correlated with the faster basal melt regions of the ice sheet and glaciers. The crustal thickness map provides constraints for an improved interpretation of the Iceland hotspot track in northern Greenland at about 100–70 Ma.