On the identification of textural equilibrium in rocks using dihedral angle measurements

Abstract

Three-dimensional numerical simulations have been constructed to investigate the distributions of apparent dihedral angles expected in unequilibrated rock textures for comparison with those expected in equilibrated rock textures. For unequilibrated, fully crystallized monomineralic rocks, the simulation shows that the distribution of apparent dihedral angles is nonrandom and similar to that expected from an equilibrated rock, and is largely independent of crystal shape and crystal nuclei distribution. This new distribution, together with the one previously derived for an equilibrated texture, defines a pair of apparent dihedral angle curves which encompass curves corresponding to any degree of textural equilibrium within a monomineralic rock. The location of a measured curve within this range allows a quantitative assessment of the degree of textural equilibrium within that rock. The simulations also show that unequilibrated, partially crystallized rocks generate apparent dihedral angle distributions for closed triangular pores that, depending on crystal shape, may mimic equilibrated dihedral angle distributions. They also indicate that unless a rock is in complete equilibrium, different dihedral angle distributions are produced by measuring the apparent dihedral angles of closed triangular or open nontriangular pores. An important conclusion of this work is that apparent dihedral angle curves for unequilibrated textures are similar to those for equilibrated textures. Therefore care must be taken when interpreting textural equilibrium from apparent dihedral angle curves.