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| Titel |
Fluid pressure and reaction zone formation at a lithological interface |
| VerfasserIn |
Benjamin Malvoisin, Yuri Podladchikov |
| 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 |
250097251
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| Publikation (Nr.) |
 EGU/EGU2014-12811.pdf |
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| Zusammenfassung |
| Chemical composition variations in reaction zones between two distinct lithologies are
generally interpreted in terms of chemical potential gradients and diffusion process.
Concentration profiles can then be used to quantify the species diffusion coefficients or the
time scale of geological events. However, chemical potential gradients are also functions of
temperature and pressure and local variations of these parameters can thus potentially modify
the diffusion process. In northern Corsica, a centimeter scale reaction zone formed under
blueschist conditions at a serpentinite – marble contact of sedimentary origin. Three
sub-zones having chemical compositions evolving from one rock end-member to
another divide the reaction zone along sharp interfaces. At the reaction zone – marble
interface, marble decarbonation occurs to form wollastonite and carbonaceous matter.
Thermodynamic calculations for this reaction and the respective increase in density of 25 %
and 7 % in the bulk rock and in the garnet minerals are interpreted as records of a
pressure gradient during reaction zone formation. Moreover, the formation of a
volatile-free sub-zone in the reaction zone from reaction between the H2O-bearing
serpentinite and the CO2-bearing marble released fluids at the contact. The impact of such
a release on the fluid pressure was modelled by considering the effects of both
the rock compaction and the transport of fluid by hydraulic diffusion. Modelling
results indicates that > 0.5 GPa fluid overpressure can be generated at the contact
if devolatilization rates are of the order of the one experimentally measured (>
10-5 kg of fluid/m3 of rock/s). The resulting pressure gradient is of the order of
magnitude of the one necessary to counter-balance the effect on chemical potential of
the chemical composition variations across the contact. Finally, after the reaction
has run to completion, the model predicts that fluid rapidly diffuses away from
the interface which thus stops reacting and is preserved during its exhumation. |
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