Fluid channelization at the submicroscopic scale in exsolved orthoamphiboles
Smelik, Eugene A.
European Journal of Mineralogy Volume 7 Number 4 (1995), p. 825 - 834
published: Aug 1, 1995
manuscript accepted: Jan 30, 1995
manuscript received: Oct 26, 1994
ArtNo. ESP147050704010, Price: 29.00 €
Abstract Transmission electron microscope study of incipient alteration of exsolved orthoamphiboles has shown that the planar exsolution microstructure exerts a strong influence on the fluid pathways during the initial stages of hydration. The exsolution microstructure consists of (010) or (120) lamellar mixtures of anthophyllite and gedrite. As the metamorphic fluids infiltrate the amphibole grains, the gedrite lamellae are preferentially attacked by the reactive fluid, being transformed to a mixture of chlorite plus quartz. The anthophyllite lamellae remain relatively unaffected by the fluid and thereby act as walls between the narrow channels of advancing fluid. The ability of the exsolution microstructure to channelize fluids depends on the scale of the lamellae, with the coarsest microstructures being the most effective. The majority of chlorite domains are coherently intergrown with the gedrite with a*amph || c*chl- Analytical electron microscope data allows the formulation of the following hydration reaction: 1.0 gedrite + 0.24 Fe2+ + 1.56 Mg2+ + 6.46 H2O -> 1.51 chlorite + 1.64 quartz + 0.53 Na+ + 0.01 Mn2+ + 2.84 H+.