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| Titel |
Estimation of lithospheric extension by accounting for stretching and thinning of the sedimentary basin - An example from the Vøring margin, NE Atlantic |
| VerfasserIn |
M. Wangen, J. I. Faleide |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250024130
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| Zusammenfassung |
| The Vøring basin offshore west of mid-Norway has formed as a result of several rift phases
since the end of the Caledonian orogeny in Ordovician-Silurian times. The last
(Late Cretaceous and Paleocene) rift phase ended with continental break-up of the
Norwegian-Greenland Sea and magmatisme. Here we report results of a study where we have
estimated the magnitude of extension and the tectonic evolution of a transect from the Vøring
margin. The amount of stretching and thinning the crust has undergone is often measured by
the so-called β-factor, which can be estimated from back-stripping of the basin and the
corresponding tectonic subsidence. Such an approach does not take into account that the
sedimentary basin is also stretched and thinned. In the Vøring basin, where the
sediments may be thicker than the crust, it is important that also sediments and not only
the crust have undergone extension. Here we suggest a simple procedure for the
estimation of the β-factors, which takes into account that the sedimentary basin is
stretched and thinned during the rifting phases. This approach approximates the
deformations of the basin by pure shear. The pore space of the sediments follows
the flow during pure-shear deformation, which is a simple approach that assures
mass conservation. The basin and the crust are assumed to deform with the same
β-factor. The procedure is demonstrated on a 2-D transect that spans the entire
Vøring margin, from close to the continental-ocean boundary to near the main land
Norway. The transect has thick Cretaceous formations, which is a characteristic
feature of the sub-basins of the western part of the Vøring margin. The β-factors
are computed for the case of four rift phases, but it is straightforward to do the
same computation for more or less rift phases. The β-factors are compared with
corresponding β-factors that do not include the effect of the extension and thinning of the
sediments. The results show that the new procedure yields a larger β-factor for the first
(Devonian) rift phase. The same applies for the Late Jurassic rift phase, which also
becomes stronger. The Late Cretaceous and Paleocene rift phase becomes considerably
weaker. The results, including a stronger Late Jurassic rift phase, explain better the
formation of the accumulation space needed for the thick Cretaceous formations.
The β-factors for each rift phase are given by simple expressions that allows for a
sensitivity study. For example, it is shown that at an increase in the paleo water
depth by 500 m increases the β-factor by Îβ = 0.14 when the rift phase has a
β = 2. |
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