A boundary layer-induced immiscibility in naturally re-equilibrated H2O-CO2-NaCl inclusions from metamorphic quartz (Western Carpathians,Czechoslovakia) |
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| Authors: | Vratislav Hurai Elfrun-Erika Horn |
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| Institution: | (1) Geochemisches Institut, Georg-August Universität, Goldschmidtstrasse 1, W-3400 Göttingen, Germany;(2) Institut für Geologie und Dynamik der Lithosphäre, Georg-August Universität, Goldschmidtstrasse 3, W-3400 Göttingen, FRG;(3) Present address: Geological Institute, Comenius University, 84215 Bratislava, Czechoslovakia |
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| Abstract: | Naturally re-equilibrated fluid inclusions have been found in quartz crystals from alpine fissures of the Western Carpathians. Re-equilibration textures, such as planar arrangement of the decrepitation clusters as well as the quartz c- and a-axis oriented fracturing indicate explosion of fluid inclusions. The extent of fracturing, which is dependent on inclusion diameters, suggests inclusion fluid overpressures between 0.6–1.9 kb. Microthermometry data are controversial with the textures because of indicating roughly fixed initial fluid composition and density during re-equilibration, although inclusion volumes have been sometimes substantially reduced by crystallization of newly-formed quartz. It is concluded that fluid loss from re-equilibrated inclusions must have been compensated for by replacing equivalent quartz volume from cracks into parent inclusion. Such a mechanism has operated in a closed system and the re-equilibration related cracks have not been connected with mineral surface. The compositional and density differences between aqueous inclusions in decrepitation clusters and CO2-rich parent inclusions cannot be interpreted in terms of classical fluid immiscibility. Moreover, monophase liquid-filled aqueous inclusions and coexisting monophase CO2 vapour-filled inclusions in the decrepitation clusters are thermodynamically unacceptable under equilibrium metamorphic conditions. The effect of disjoining pressure resulting from structural and electrostatic forces in very thin fractures is suspected to have caused density and compositional inconsistencies between parent and cluster inclusions, as well as the unusual appearance of cluster inclusions. In high-grade metamorphic conditions, the re-equilibration probably leads to boundary layer-induced immiscibility of homogeneous H2O–CO2–NaCl fluids and to formation of compositionally contrasting CO2-rich and aqueous inclusions. |
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