Some effects of lateral heterogeneities in the upper mantle on postglacial land uplift close to continental margins

Abstract

S U M M A R YWe investigate the effects of lateral heterogeneities in the upper mantle on the calculation of postglacial land uplift. For the model calculations we use a commercial finiteelement code, which enables us to solve the equations governing a layered, isotropic, incompressible, Maxwell-viscoelastic half-space with laterally varying layer thicknesses and physical properties. Following previous investigations performed by Sabadini, Yuen & Portney (1986) and Gasperini & Sabadini (1989), we extend their results using a more realistic loading history and different earth models. We then focus our attention on the question whether lateral heterogeneities in the upper mantle can be modelled correctly using a set of homogeneous earth models. To this end, a comparison of model calculations using both laterally homogeneous and heterogeneous earth models is performed.We find that lateral heterogeneities in the upper mantle significantly influence the calculated postglacial land uplift. The resolving power of relative sea-level observations for the prescribed lateral heterogeneities used in this study is mainly focused on observations around the load margin and outside the glaciated areas, where differences in predicted land uplift between individual models are large enough to be resolved by observations.We can qualitatively determine lateral heterogeneities in the upper mantle using a set of laterally homogeneous earth models, if the geological structure, for example a continental margin, is known. However, in order to infer the correct values of lithospheric thickness and asthenospheric viscosity, we need to use laterally heterogeneous models.

Using postglacial sea level, crustal velocities and gravity-rate-of-change to constrain the influence of thermal effects on mantle lateral heterogeneities

“…3-6 also shows that for sites within the ice margin, the effect ofˇon the RSL curves is generally small, but generally larger at the ice-sheet margin (e.g., sites 323, 235, 282 and 570). This confirms an earlier finding (e.g., Kaufmann et al, 1997;Wu and van der Wal, 2003;Wang and Wu, 2006b;Wu, 2006) that RSL data at sites near the ice margin are most sensitive to lateral viscosity variations in the mantle.…”

“…However, those early works were based on flat-earth models with simplistic ice models, which include lateral variations in lithospheric thickness, asthenospheric viscosity (e.g., Sabadini et al, 1986;Kaufmann et al, 1997), deeper mantle viscosity and lateral density variation (Wu, 1998). These works show that the effect of lateral viscosity variation on relative sea levels (RSL) and land uplift rate can be comparable to the effect of radial viscosity variation.…”

An Estimate of Global Mean Sea-level Rise Inferred from Tide-gauge Measurements Using Glacial-isostatic Models Consistent with the Relative Sea-level Record

“…the change between continental and oceanic lithospheres (e.g. KAUFMANN et al, 1997;OKUNO and NAKADA, 2001;MARTINEC and WOLF, 2005).…”

Glacial isostasy and plate motion

“…Due to computational rigor inherent to the modelling of viscoelastic lateral heterogeneities, various approximations, such as introducing some symmetries like a twodimensional (2D) structure for a half-space model (Sabadini et al, 1986;Kaufmann et al, 1997) or axial symmetry for a spherical earth model (e.g. Wu and van der Wal, 2003;Martinec and Wolf, 2005;Klemann et al, 2007) have been employed in past work.…”