Nature and Dynamic Interpretation of Deformation Lamellae in Calcite of Three Marbles.

摘要

The fabrics of three crystalline marbles lacking obvious effects of post-crystalline granulation are described in detail. Particular attention is paid to (0112) lamellae optically recognizable as twins. These have restricted ranges of orientation from which it is possible to deduce simple systems of applied stress that could account for observed twinning. The procedure followed in developing this dynamic interpretation of twin lamellae is described. The orientation of c axes and that of visible (0112) lamellae in grains lacking recognizable twinning can also be explained in terms of the same system of applied stress in any given case. It is concluded that preferred orientation patterns of c axes of calcite were determined during the main phase of metamorphism, but visible (0112) lamellae reflect a very late phase of incipient deformation. The above dynamic interpretation of natural marble fabric is based on experimental data and on fabrics observed in experimentally deformed marbles. Most visible lamellae in the three specimens described are parallel to (0112). A few are partings parallel to (0112). No other types of lamellae were recorded. jg.