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| Titel |
Tilting of post-glacial Fennoscandian shorelines requires a low-viscosity asthenosphere |
| VerfasserIn |
W. Fjeldskaar, A. Amantov |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250059503
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| Zusammenfassung |
| The Fennoscandian uplift has been intensely studied and discussed since the 18th century and
it is now widely accepted to be an isostatic response to the recent deglaciation. Our
knowledge of the fluid properties of the Earth comes largely from its uplift response to load
redistributions that occurred over the last ice age. The elevation of past shorelines and the
present rate of land uplift constrain the fluid properties of the mantle and the elastic rigidity of
the lithosphere.
The post-glacial uplift in Fennoscandia has been mapped by the following means:
Shorelevel displacement curves, showing the vertical displacement at a certain
location,
Shoreline diagrams, showing the displacement and tilting of palaeo shorelines,
Present-day uplift monitored by tide gauge, old water marks, GPS observations
and by satellite missions.
We have now revisited the Fennoscandian uplift, and done high resolution (10 km
spatial) modelling which includes glacial isostasy, hydro isostasy and sediment
isostasy. The Earth’s response to glaciers and sediments has been modeled by using a
layered viscous model overlain by an elastic lithosphere. In the calculations we
have used the tilting of the palaeo shorelines as to constrain the Earth rheology.
Different kinds of data constrain different parameters. It has been shown that the
tilting of paleoshorelines is very sensitive to the mantle viscosity and lithosphere
rigidity.
Five sites along the Norwegian coast with observed paleoshoreline tilts have been
selected for the present investigation; western Norway (Sotra Island and Sunnmøre), mid
Norway (Trøndelag) and northern Norway (Lofoten and Finnmark). The observed tilts vary
from 0.6 m/km (northern Norway) to 1.7 m/km (mid Norway). The theoretical palaeo
shoreline tilts were calculated with different deglaciation models, and with a range of Earth
rheology models. There are significantly variations in the calculated tilts, and the best fit with
the observed tilts from Younger Dryas (last 12Â 000 years) was achieved with a low-viscosity
asthenosphere of thickness less than 150 km and viscosity less than 7.0x1019 Pa s above a
mantle of viscosity 1021 Pa s, and an effective elastic lithosphere thickness of 40 km (flexural
rigidity 1024 Nm). |
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