The rates and extent of textural equilibration in high-temperature fluid-bearing systems

The geometry of fluid-filled pores in texturally equilibrated aggregates ca n, in theory, be uniquely determined given the porosity and the equilibrium dihedral angle for all possible orientations and combinations of the const ituent solid phases. While it is useful to be able to do this, one should a lso ask whether, and to what extent, textural equilibrium is actually attai ned during fluid-present intervals in high-temperature rocks. In fact, text ural equilibrium may be only rarely attained during melting of crustal rock s, and equilibration under mid-ocean ridges is possibly incomplete to depth s as great as the garnet stability zone. There is very little published inf ormation on the rates of attainment of textural equilibrium in fluid-bearin g geological environments. The available experimental data for the rates of growth of equilibrated domains are consistent with a power-law relationshi p between domain size and equilibration time with an exponent between 2 and 3. A simplified theoretical treatment of pore shape change governed by the Gibbs-Thompson relationship demonstrates that an exponent of 3 is to be ex pected for equilibration by diffusion within the fluid phase, with an effec tive diffusivity consistent with the available data. (C) 2000 Elsevier Scie nce B.V. All rights reserved.