Abstract:

The geodynamic context of Iceland provides the rare opportunity to analyse the combined effects of a ridge and a hotspot on deformation processes. From a digital elevation model, field analysis and a compilation of previous work, we propose a synthesis of vertical motions of Iceland during the Holocene with a focus on the post-glacial rebound. We determined two ancient marine limits, one above and one below the present sea level, estimated at 10 ka ± 300 years and 8150 ± 350 years bp, respectively. We calculated an uplift phase of 40–170 m with a rate of 2.1–9.2 cm a−1 between 10 ka ± 300 years and 8150 ± 350 years bp, corresponding to the post-glacial rebound of Iceland following the Weichselian glaciation. Spatial variations of the rebound are mainly related to the local glacial dynamics (ice load and deglaciation history) rather than the geodynamic context. However, the relaxation time deduced from uplift data is 4167 years in west Iceland and 2000 years in SSW Iceland. We estimated viscosity from relaxation time, ranging from 2.1 × 1019 Pa s to 3.2 × 1019 Pa s. The significant difference in the relaxation time is due to local variation of the lithospheric thickness as a result of rifting rather than because of a variation of the viscosity.

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