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| Titel |
A generic model of pattern formation in Mississippi Valley-Type deposits based on analytical findings |
| VerfasserIn |
Ulrich Kelka, Manolis Veveakis, Nicolas Beaudoin, Thomas Poulet, Daniel Koehn, Klaus Regenauer-Lieb, Peter Chung, Jasper Berndt |
| 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 |
250133258
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| Publikation (Nr.) |
 EGU/EGU2016-13847.pdf |
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| Zusammenfassung |
| Rhythmically banded dolomites (zebra dolomite) are found worldwide, and are
frequently associated with mineralization of the Mississippi Valley-Type (MVT). These
rocks consist of dark fine grained and impurity-rich layers alternating with light
coarse grained and virtually impurity-free layers. The texture of the light layers is
similar to the one of tectonic syntaxial veins where crystals grow towards a median
line.
We present petrographic and chemical analysis of zebra dolomite samples from the San
Vicente mine, Central Peru. The applied methods are petrographic microscopy, SEM, EBSD,
EMP and LA-ICP-MS. The findings influence the development of a generic model of pattern
formation.
We found the density and the distribution of second-phase material to be one striking
feature. The impurities are accumulated in the dark layers, which show an even higher density
of second-phase material than the surrounding impurity-rich dolomite. With CL, it was
possible to detect a luminescent structure in the center of the light bands which seems to be
present independent of the thickness and spacing of the respective layers. This structure was
analysed in more detail with EMP. We further found that the dolomite crystals in the
dark and light layers are chemically similar but show a variation in some trace
elements.
Based on the analytical findings, we put forward a mathematical model of zebra dolomite
formation based on Cnoidal waves. We believe that the light coarse grained layers represent
hydromechanical instabilities arising during the diagenetic compaction of a fluid saturated,
impurity-rich dolomite. Our approach is based on the extension of the classical compaction
bands theory to a viscose, non-linear rheology. In the model, the spacing between two light
coarse grained layers is linked to the compaction length during the pattern formation. With
the formulation of a 1D steady-state solution we can relate the genesis of the structure to
physical parameter, such as permeability and pressure. By this procedure field data can be
applied in order to invert for permeability and pressure. Our model can therefore help to
develop a new tool for field geologists and might as well be applicable to several other
geological problems. |
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