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| Titel |
Crustal uplift of the Precambrian cratons due to metamorphism in crustal rocks under infiltration of mantle fluids |
| VerfasserIn |
Eugene Artyushkov, Peter Chekhovich, Sergey Korikovsky, Hans-Joachim Massonne |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250141952
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| Publikation (Nr.) |
 EGU/EGU2017-5514.pdf |
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| Zusammenfassung |
| Precambrian cratons cover about 70% of the total area of the continents. During the last
several million years cratonic areas underwent rapid uplift, from 100-200 m in East Europe to
1000-1500 m Southern Africa. Shortening of the Precambrian crust terminated half a billion
years ago or earlier and this popular mechanism cannot be applied to its recent uplift. Large
thickness of cratonic mantle lithosphere, 100-200 km in most regions, together with its low
density precludes delamination of this layer and magmatic underplating as possible causes of
recent uplift.
It cannot be precluded that in some cratonic regions recent uplift occurred due to
delamination of the lower part of mantle lithosphere with the density increased by
metasomatism. Even a small uplift of ≥ 100-200 m would require delamination of a thick
layer of mantle lithosphere. As a result a temperature drop of > 200 C would arise at the base
of the lithosphere producing a shear wave velocities drop of > 2%. According to the seismic
tomography data such a drop in VS is observed only in some regions with the Precambrian
lithosphere, e.g., in Northeastern Africa.
Spatial distribution of the Precambrian cratons is quite different from that predicted by the
main models of dynamic topography in the mantle. Moreover, many uplifted blocks are
bounded by steep slopes hundreds of meters to one kilometer high and only tens
of kilometers wide. Such slopes could not have been formed by bending of thick
cratonic lithosphere under the forces acting from below. Their recent formation
indicates rock expansion within the crust at shallow depth comparable with the slope
width.
Rocks formed at the pressure P ∼ 0.5-1.0 GPa are widespread on the Precambrian
cratons. This indicates that during their lifetime a layer of rocks ∼ 15-30 km thick has
been removed from the crustal surface by denudation. As a result rocks which were
initially located in the lower crust emerged to the middle or upper crust. Due to
metamorphic reactions under the new P-T conditions the density of rocks would become
considerably lower. The analysis of phase diagrams of typical crustal rocks shows
that the associated expansion of rocks could produce the crustal uplift up to 2000
m. However no metamorphism occurred in rocks as long as they remained dry.
Rapid uplift of the Precambrian cratons during the last several million years can
indicate infiltration into the crust of fluids from the mantle. The volume of fluid
infiltrated into the crust should be comparable with the cumulate volume of the
Neotectonic crustal uplift. Under such circumstances it can be expected that in some
Precambrian regions a fluid rich layer now exists within the crust. It should be
characterized by a high electrical conductivity and decreased S-wave velocities. |
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