Fluid Immiscibility in the Central Alps

Title data

Mullis, Josef ; de Capitani, Christian ; Kirschen, Marcus:
Fluid Immiscibility in the Central Alps.
1996
Event: Goldschmidt 1996 Conference , 31. März - 4. April 1996 , Heidelberg.
(Conference item: Conference , Paper )

Related URLs

Abstract in another language

Multicomponent CH4-CO2-H2O-NaCl fluids show miscibility gaps at temperatures below 400°C. Implications of this are expected to be found in diagenetic and low-grade metamorphic terrains in the Central Alps. A systematic search revealed fluid immiscibility in three distinct fluid environments:
1. CH4-H2O-salt: in diagenetic and low-grade anchizonal, hydrocarbon bearing sedimentary rocks.
2. CO2-H2O-salt: at high-grade anchizonal and greenschist facies conditions in carbon and carbonate bearing meta-sedimentary and meta-igneous rocks.
3. N2-H2O-salt: at anchizonal and greenschist facies conditions in ammonium bearing meta-sedimentary and meta-igneous rocks.
In addition to the major volatile component, fluids may contain smaller amounts of CH4, CO2, N2, H2S. Observations of natural fluid systems permit to distinguish six different geological processes that lead to fluid immiscibility:
1. Isobaric decrease in temperature
2. Isothermal decrease in pressure
3. Input of salt-enriched fluids (salting out)
4. Volatile production during cracking of kerogen and higher hydrocarbons and by decarbonation and oxidation or reduction of carbonaceous matter.
5. Upward and downward movement of the gas-water contact mimicking unmoving phenomena
6. Channeled influx of unmixed allochtonous volatiles
Depending on the tectonic-metamorphic and lithologic environment, fluid immiscibility in the Central Alps is controlled by one of several unmixing processes:
- In CH4 bearing diagenetic and low-grade anchi-metamorphic rocks, unmixing process 1, 2, 4, 5, 6 are dominant.
- In CO2 bearing rocks that suffered high-grade anchizonal and greenschist facies conditions, unmixing process 2 and 6 are dominant.
- In N2 bearing rocks exposed to anchizonal and greenschist facies conditions, unmixing process 2 is dominant.
- In rocks containing little or no volatiles, process 6 is connected to fractures and faults.