Weakened Lithosphere Beneath Greenland Inferred From Effective Elastic Thickness: A Hot Spot Effect?

The effective elastic thickness (T-e) of the lithosphere provides geophysical information about long-term flexural strength and can be used to constrain thermorheological properties of the lithosphere. T-e is typically calculated from the spectral analysis of gravity and topography data; variations in T-e are, however, not well resolved in Greenland due to poor constraints on crustal structure (including crustal thickness) and complications due to ice loading. In addition, geological and geophysical constraints on the tectonic history of Greenland are sparse due to the thick ice cover. Here we use the global gravity model EIGEN-6C4 together with a new model of the crust-mantle boundary to obtain a high-resolution T-e map of Greenland. The distribution of T-e indicates reduced strength in the lower crust and lithospheric mantle beneath southern and central Greenland, which may be due to the passage of the Iceland hot spot during the last 100Ma. In contrast, the northern part of Greenland shows a large T-e, implying mechanical coupling between crust and uppermost mantle and suggesting the existence of a cold and strong tectonic unit. In a relative sense, the distribution of T-e values is consistent with estimates of lithospheric thickness based on seismic velocity models, indicating a dominantly thermal control on lithospheric structure and evolution. Plain Language Summary Greenland is covered by a large ice sheet; its geodynamic history is therefore mostly unknown as only the coastal areas are accessible for direct geological sampling. However, geophysical data can be used to investigate the lithospheric structure to infer its geodynamic history. Here we use satellite gravity data together with elevation data and a crustal density model to look at the distribution of the effective elastic thickness, which provides information about the variations in strength of the lithosphere. We find that most of Greenland's lithosphere is weaker than expected given its age of formation (approximate to 1 billion years), suggesting that it was affected by a thermal event within the last approximate to 400 million years. We interpret the weakness in the lithosphere as a result of the movement of Greenland with respect to hot mantle material, which is now located beneath Iceland leading to large volcanism there. The results of this study show for the first time the effect of the hot mantle material on the lithosphere of Greenland, which can help us identify the different possible tracks of the moving hot mantle material and understand the stability of the ice sheet.