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| Titel |
Compaction instabilities described by cnoidal waves in ore-hosting dolomites |
| VerfasserIn |
Ulrich Kelka, Manolis Veveakis, Nicolas Beaudoin, Thomas Poulet, Daniel Koehn, Klaus Regenauer-Lieb |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250132942
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| Publikation (Nr.) |
 EGU/EGU2016-13497.pdf |
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| Zusammenfassung |
| Rhythmically banded dolomites are found worldwide, and are frequently associated with
mineralization of the Mississippi Valley-Type (MVT). These rocks, referred to as zebra
dolomites, are built up by alternating dark and light layers of chemically similar dolomite.
Apart from the color, a considerable difference in grain size and impurity content is
observable comparing the different layers. The grain size and impurity content can differ by
several orders of magnitude between the coarse grained light and the fine grained dark bands.
In addition to that, the crystals in the light, virtually impurity-free bands are elongated
towards a central line in these layers. This gives them a texture similar to syntaxial veins,
where crystals grow from the rims of an opening fracture towards the center of the crack. The
structure has been studied by several authors and different generic models have been
proposed. Nonetheless, a complete model which can explain all features has not been
developed, yet.
We present a new generic model of a coupled solid-fluid system which is able to relate
the spacing of the respective layers to physical parameters such as pressure and
permeability. The model is a 1D steady-state solution based on Cnoidal waves. In
our approach the light coarse grained layers of the zebra dolomites are related to
instabilities developing during the diagenetic compaction of fluid saturated carbonates.
These compaction instabilities form high permeability channels in which an elevated
pressure arises. The dolomite in these channels recrystallizes, forming a secondary,
impurity free generation of crystals. The subsequent grain growth is influenced by the
distribution of impurities, and is most effective in the minerals of the second dolomite
generation. During the progressive grain coarsening a fracture can develop in the
central part of the light layers along which dissolution occurs. The crystals will then
grow towards this fracture leading to the elongated shape of the grains. The model
can explain the equidistant spacing of the layers, the grain size difference of the
zebra bands, and might also explain the elongated shape of the crystals in the light
layers.
Because our model relates the structure to certain rheologic parameters, we believe that
this approach might help to increase the understanding of economic mineralization of the
MVT. |
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