Andalusite-bearing veins at Vedrette di Ries (eastern Alps, Italy): fluid phase composition based on fluid inclusions

Andalusite-bearing veins formed during contact metamorphism in the aureole of the Vedrette di Ries tonalite. In the veins, quartz crystals that are completely armoured by andalusite or that occur in strain shadow areas contain three generations of fluid inclusions: low-salinity H,O-CO,-CH, mixtures with CHJ(C0, + CH,) 5 0.35 (type A); low-salinity aqueous fluids (type B); H,O-free, C02-CH, fluids with the same carbonic speciation as A (type C). Carbonic types A and C typically have a dark appearance, which is attributed to graphite coatings on inclusion walls. Microstructural analysis of the host quartz and calculated densities indicate that type A inclusions were likely trapped during vein formation. These inclusions underwent strain-assisted re-equilibration during cooling that resulted in density increases without change of composition. After the rocks had cooled below about 350" C, type C inclusions appear to have formed from one of the immiscible fractions after unmixing of the H20-C02-CH, fluid mixtures. Aqueous type B inclusions, apparently trapped between 225 and 350" C, could represent an independent fluid, or could be the H,O-rich fraction of unmixed type A fluids. Taking account of the uncertainties, the composition and density of the complex type A inclusion fluids are in good agreement with the properties of primary fluids calculated from the petrological data. The fluid inclusion data support the model of vein formation by hydrofracturing as a result of dehydration of graphitic metapelites. These new results also demonstrate the importance of considering strain in the interpretation of metamorphic fluid inclusions.

[1]  E. L. Johnson,et al.  Syndeformational fluid trapping in quartz: determining the pressure-temperature conditions of deformation from fluid inclusions and the formation of pure CO2 fluid inclusions during grain-boundary migration , 1995 .

[2]  J. Connolly.  Phase diagram methods for graphitic rocks and application to the system C−O−H−FeO−TiO2−SiO2 , 1995 .

[3]  J. Dubessy,et al.  vX properties of CH 4 -CO 2 and CO 2 -N 2 fluid inclusions; modelling for T<31 degrees C and P<400 bars , 1994 .

[4]  Bernardo Cesare,et al.  Synmetamorphic veining: origin of andalusite‐bearing veins in the Vedrette di Ries contact aureole, Eastern Alps, Italy , 1994 .

[5]  B. Cesare.  Hercynite as the product of staurolite decomposition in the contact aureole of Vedrette di Ries, eastern Alps, Italy , 1994 .

[6]  R. Bakker,et al.  A mechanism for preferential H2O leakage from fluid inclusions in quartz, based on TEM observations , 1994 .

[7]  J. Connolly,et al.  C‐O‐H‐S fluid composition and oxygen fugacity in graphitic metapelites , 1993 .

[8]  B. Mukhopadhyay,et al.  A reevaluation of the stability relations of andalusite: Thermochemical data and phase diagram for the aluminum silicates , 1993 .

[9]  I. Chou,et al.  Re-equilibration of CO2fluid inclusions at controlled hydrogen fugacities , 1993 .

[10]  L. Diamond.  Stability of CO2 clathrate hydrate + CO2 liquid + CO2 vapour + aqueous KCl-NaCl solutions: Experimental determination and application to salinity estimates of fluid inclusions ∗ , 1992 .

[11]  J. C. Seitz,et al.  Theoretical and practical aspects of differential partitioning of gases by clathrate hydrates in fluid inclusions , 1990 .

[12]  R. Bodnar,et al.  Methane in fluid inclusions from granulites: A product of hydrogen diffusion?☆ , 1990 .

[13]  L. Hollister.  Enrichment of CO2 in fluid inclusions in quartz by removal of H2O during crystal-plastic deformation , 1990 .

[14]  P. E. Brown.  FLINCOR; a microcomputer program for the reduction and investigation of fluid-inclusion data , 1989 .

[15]  J. Dubessy,et al.  Advances in C-O-H-N-S fluid geochemistry based on micro-Raman spectrometric analysis of fluid inclusions , 1989 .

[16]  D. Kerrick.  Al2SiO5-bearing segregations in the Lepontine Alps, Switzerland: Aluminum mobility in metapelites , 1988 .

[17]  J. C. Seitz,et al.  Characterization of CO2CH4H2O fluid inclusions by microthermometry and laser Raman microprobe spectroscopy: Inferences for clathrate and fluid equilibria , 1987 .

[18]  R. Kreulen.  Thermodynamic calculations of the COH system applied to fluid inclusions: Are fluid inclusions unbiassed samples of ancient fluids? , 1987 .

[19]  B. Yardley.  Fluid Migration and Veining in the Connemara Schists, Ireland , 1986 .

[20]  M. Crawford,et al.  Metamorphic Fluids: The Evidence from Fluid Inclusions , 1986 .

[21]  J. Dubessy,et al.  The P-V̄-T-X-f O2 evolution of H2O-CO2-CH4-bearing fluid in a wolframite vein: Reconstruction from fluid inclusion studies , 1985 .

[22]  J. Holloway.  Graphite-CH4-H2O-CO2 equilibria at low-grade metamorphic conditions , 1984 .

[23]  H. Helgeson,et al.  Calculation of the thermodynamic and geochemical consequences of nonideal mixing in the system H 2 O-CO 2 -NaCl on phase relations in geologic systems; metamorphic equilibria at high pressures and temperatures , 1983 .

[24]  R. Burruss.  Analysis of fluid inclusions; phase equilibria at constant volume , 1981 .

[25]  D. M. Kerrick,et al.  A modified Redlich-Kwong equation for H 2 O, CO 2 , and H 2 O-CO 2 mixtures at elevated pressures and temperatures , 1981 .

[26]  P. Collins.  Gas hydrates in CO 2 -bearing fluid inclusions and the use of freezing data for estimation of salinity , 1979 .

[27]  H. E. C. Swanenberg.  Phase equilibria in carbonic systems, and their application to freezing studies of fluid inclusions , 1979 .

[28]  F. P. Sassi,et al.  On the age of the Vedrette di Ries (Rieserferner) massif and its geodynamic significance , 1979 .

[29]  H. Ohmoto,et al.  Devolatilization equilibria in graphitic systems , 1977 .

[30]  R. Kerrich.  Some effects of tectonic recrystallisation on fluid inclusions in vein quartz , 1976 .

[31]  L. Hollister,et al.  Phase equilibria in fluid inclusions from the Khtada Lake metamorphic complex , 1976 .

[32]  R. D. Gray,et al.  A modified Redlich‐Kwong equation of state , 1970 .

[33]  B. Skinner,et al.  Experimental evidence that fluid inclusions do not leak , 1968 .

[34]  H. Barnes,et al.  Geochemistry of Hydrothermal Ore Deposits , 1968 .

[35]  TBRese SurBn Bowr.  Calculation of the thermodynamic and geochemical consequences of nonideal mixing in the system H 2 OCO 2-NaCI on phase relations in geologic systems : metamorphic equilibria at high pressures and temperatures , 2022 .