Deglacial land emergence and lateral upper-mantle heterogeneity in the Svalbard Archipelago-I. First results for simple load models

Abstract

The glacial-isostatic adjustment following the removal of the Pleistocene ice sheets furnishes basic information on the thickness of the Earth's lithosphere and the viscosity of the subjacent mantle. Paper I is concerned with an elementary interpretation of the post-glacial land emergence observed at a restricted set of six locations in the Svalbard Archipelago. The interpretation is based on a three-layer, incompressible Maxwell-viscoelastic earth model, which is forced by a time-dependent load distribution simulating the deglaciation history of the Svalbard Archipelago and the Barents Sea. In view of inconclusive geomorphological evidence suggesting either total or partial glaciation of the area at glacial maximum, two simple load models, BARENTS-T1 and BARENTS-P1, are considered in the first instance. A comparison between the calculated and observed values of land emergence suggests increases in lithosphere thickness and asthenosphere viscosity with increasing distance of the location from the continental margin. The trends are qualitatively insensitive to the load model, load thickness or load cross-section used. For load model BARENTS-T1 with parabolic cross-section, an initial load thickness of 1.50 km and a relaxed fitting criterion, the lateral variations are only weak. If a more restrictive fitting criterion is employed, the variations become more prominent and suggest increasing values of lithosphere thickness from below 80 km to above 140 km and of asthenosphere viscosity from below 3 × 1018 Pa s to above 2 × 1019 Pa s over a distance of about 300 km. In Paper II (Kaufmann & Wolf 1995), a high-resolution load model and an extended set of land-emergence observations are used to study further the possibility of resolving lateral heterogeneity in the upper mantle below the Svalbard Archipelago.