Stephen Centrella's seminar, University of Pau

Relationship between density, volume and mass transfer through a fluid phase during hydration reactions in the Bergen Arcs, Norway

Abstract

Mineral replacement take place by dissolution-reprecipitation processes. All processes such as chemical weathering, leaching, metamorphism, metasomatism and diagenesis are all linked by common features where one mineral or mineral assemblage is replaced by one or more stable assemblage. The Bergen Arcs is located in the western coast of Norway near the city of Bergen. During the Greenvillian Orogeny, this region in particular the Lindås Nappe experienced a granulite-facies metamorphism at pressures less than 10kbar and around 800-850°C. During the Caledonian orogeny the Lindås Nappe has been affected by a partial eclogite and amphibolite facies. Both metamorphic facies occur along brittle fracture where the fluid enters and reacts into the shear zone through the granulite. This region provides a natural laboratory to better understand metamorphic reactions from a regional to millimetre scale. Because the interface between these three metamorphic facies is very sharp, it provides an exceptional site to determine the mechanism of metamorphic reactions.

Mineral replacement take place by dissolution-reprecipitation processes. All processes such as chemical weathering, leaching, metamorphism, metasomatism and diagenesis are all linked by common features where one mineral or mineral assemblage is replaced by one or more stable assemblage.
The Bergen Arcs is located in the western coast of Norway near the city of Bergen. During the Greenvillian Orogeny, this region in particular the Lindås Nappe experienced a granulite-facies metamorphism at pressures less than 10kbar and around 800-850°C. During the Caledonian orogeny the Lindås Nappe has been affected by a partial eclogite and amphibolite facies. Both metamorphic facies occur along brittle fracture where the fluid enters and reacts into the shear zone through the granulite. This region provides a natural laboratory to better understand metamorphic reactions from a regional to millimetre scale. Because the interface between these three metamorphic facies is very sharp, it provides an exceptional site to determine the mechanism of metamorphic reactions.

The study of the transition from granulite to the hydrated amphibolite and eclogite shows that the bulk rock composition doesn’t change significantly during the hydration event for major and trace element (concentration). This implies element redistribution between the parent minerals, the fluid and the newly formed minerals. During the hydration reaction, rock densities and volume change generating stress in the system. P-T-X thermodynamic modelling show that eclogite and amphibolite seem to be stable at the same temperature and XCO2 but at different thermodynamic pressure.