Application of L–S fabric scheme to structural mapping and paleostrain analysis

摘要: The L–S fabric scheme, introduced by Flinn more than 10 years ago, constitutes a valuable, but largely unused tool for field geologists engaged in regional structural studies. Although there is a continuous spectrum of fabrics between pure lineation and pure foliation, Flinn defined five discrete categories, which can be readily identified in the field by experienced geologists. Several methods are available by which these field judgements may be checked. We found that there is a general tendency of overestimating the relative strength of mineral lineation and underestimating that of mineral foliation. For shape fabrics, simple geometric relations serve as safeguards in the field.Several parameters, such as Flinn's k-value, have been used to specify the strength of lineation versus that of foliation. This approach serves to quantify the L–S fabric scheme, and permits correlation between the mineral fabric and the strain ellipsoid. Relationships are most favourable where k(fabric) = k(strain). Although reliable data are scarce or still lacking, we suspect that in most metamorphic rocks k(strain) is more readily estimated than deformation magnitudes.Two examples are presented of large-scale patterns of k(shape fabric) from the Grenville Province, Ontario. In the first example, the predeformational shape of the mineral constituents is quasi-spherical, and k(fabric) presumably close to k (strain). In the second example the original shapes are inequant, and k (fabric) ≠ k (strain). But the two k-values may be close enough for qualitative comparisons between the strain patterns of the geologic structure and those of tectonic models.