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| Titel |
Carbonates in thrust faults: High temperature investigations into deformation processes in calcite-dolomite systems |
| VerfasserIn |
A. Kushnir, L. Kennedy, S. Misra, P. Benson |
| Konferenz |
EGU General Assembly 2012
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 14 (2012) |
| Datensatznummer |
250058779
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| Zusammenfassung |
| The role of dolomite on the strength and evolution of calcite-dolomite fold and
thrust belts and nappes (as observed in the Canadian Rockies, the Swiss Alps, the
Italian Apennines, and the Naukluft Nappe Complex) is largely unknown. Field
investigations indicate that strain in natural systems is localized in calcite, resulting in a
ductile response, while dolomite deforms in a dominantly brittle manner. To date,
experimental studies on polymineralic carbonate systems are limited to homogeneous,
fine-grained, calcite-dolomite composites of relatively low dolomite content. The effect of
dolomite on limestone rheology, the onset of crystal-plastic deformation in dolomite in
composites, and the potential for strain localization in composites have not yet been fully
quantified.
Constant displacement rate (3x10-4 s-1and 10-4 s-1), high confining pressure (300
MPa) and high temperature (750Ë C and 800Ë C) torsion experiments were conducted to
address the role of dolomite on the strength of calcite-dolomite composites. Experiments
were performed on samples produced by hot isostatic pressing (HIP) amalgams of a natural,
pure dolomite and a reagent, pure calcite. We performed experiments on the following
mixtures (given as dolomite%): 25%, 35%, 50%, and 75%. These synthetic HIP products
eliminated concerns of mineralogical impurities and textural anomalies due to porosity,
structural fabrics (e.g., foliation) and fossil content. The samples were deformed up to a
maximum finite shear strain of 5.0 and the experimental set up was unvented to inhibit
sample decarbonation.
Mechanical data shows a considerable increase in sample yield strength with increasing
dolomite content. Experimental products with low starting dolomite content (dol%: 25% and
35%) display macroscopic strain localization along compositionally defined foliation.
Experimental products with high dolomite content (dol%: 50% and 75%) demonstrate no
macroscopic foliation. Post-deformation microstructure analysis shows that small dolomite
grains (~50 μm) are characterized by well-defined grain
boundaries and cleavage controlled fracture. There is evidence of the interruption
of foliation development due to the presence of large-grained dolomite. Calcite
grains are characterized by triple junction grain boundaries, providing evidence
for recrystallization. Ongoing microstructural analyses (including: thin section
analysis, EBSD, SEM, and Microprobe analysis) are being conducted to better
constrain the deformation mechanisms and the degree of strain localization in these
composites.
Our experiments provide insights into the processes controlling rheology within bimodal
calcite-dolomite systems, which can be used to improve models of the evolution of fold and
thrust belt systems. |
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