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| Titel |
The wave-like geodynamic reorganizations revealed by the change in orientation of the paleostress axes |
| VerfasserIn |
Shamil Mukhamediev, Tomas Belousov |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098234
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| Publikation (Nr.) |
 EGU/EGU2014-13892.pdf |
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| Zusammenfassung |
| Sedimentary rock fracturing is a reliable stress indicator when properly measured, processed
and interpreted. Our long-term field observations and theoretical considerations show that the
primary joint sets are formed at the stage of diagenesis of sediments at horizontal bedding.
Most likely, it happens due to internal instability of sediments manifested in localised form,
which leads to formation of two conjugate systems of shear discontinuities. This
model allows us to reconstruct the orientation of the axis of the maximum horizontal
paleo-compression SH,max and to determine the period of its existence up to the scale of
geological time. During more than 30 years of our field observations, we collected
about 400,000 individual joint measurements in many regions of Eurasia. These
data were applied to paleostress reconstruction by using interpretation of primary
jointing formation mentioned above. Both spatial distributions of paleostress axes and
the evolution of these distributions in time determined by our techniques are in
reasonably good agreement with paleogeodynamic reconstructions obtained by
other approaches. A distinctive feature of the paleostress evolution is that at certain
times orientation of the SH,max axes changes abruptly, turning at an angle up to
90°. Sometimes these changes are gradually spreading to neighboring regions.
We attribute this phenomenon to the geodynamic reorganization which spreads
over the space at a certain speed. Such wave-like spreading was observed in the
East-European platform, the Tien-Shan, along the arc Pamirs-Tibet-Vietnam and in other
regions.
From the perspective of this phenomenon, the Caucasus-Zagros region is of particular
interest. Here from the end of the Early Cretaceous to the present time the SH,max axis with
small spatial variations was NE oriented. However, we identified a relatively short
period in the Miocene characterized by geodynamic reorganization. In the early
middle Miocene in the south-east of the region (the south-eastern part of the Zagros)
the SH,max axis changed orientation from NE to NW. At this time in the north of
the region (Central Pre-Caucasus) the SH,max axis was still directed towards NE.
But in the middle Sarmatian, when the southern part of the region already had NE
orientation of compression, in the northern part the SH,max axis reoriented in NNW
direction. As in the south of the region, this reorientation was short and in late
Sarmatian the SH,max axis regained his usual NE orientation. The identified short-term
restructuring that began in the south-east of the region in the early middle Miocene
and which reached the northern part of the region in the early Late Miocene can
be interpreted as the process of the south to north moving of the solitary wave of
geodynamic perturbation. The velocity of the wave is estimated as 0.1-1.0 m/year. |
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