Abstract

Synthetic Fabric Models

To aid discussion of the geometry of folds forward models are constructed to illustrate and test the inferred sequential development of folds in three thrust sheets, nappe N1 (eastern domain) and imbricates n1c and n2c (western domain). Models consist of equal-area projections of the geometries of folds of bedding and, where applicable, folds of axial surfaces. Fold axes are represented as dots with numerical subscripts indicating their respective fold sets (n = 1,2,3). Orientations of fold surfaces represented in models are those which yield good approximations to the surface orientations measured around the curvature of folds characteristic of particular fold sets. The distribution of fold surface orientations is effectively weighted by selection of surfaces to be used in subsequent stages of modeled fold development. Selection of particular fold surface orientations is made on the basis of fold style and the dominant attitude of fold surfaces which define folds of a particular fold set. As an example, a tight fold with long homoclinal limbs would, during modeled refolding of bedding, be represented primarily by the orientations of the fold limbs.

Napple N2 (Eastern Domain). Synthetic fabric diagrams constructed from a forward model of the geometry of sequential folding for nappe N2 are compared to the observed fabric in Figure 10. First folds are modeled as a tight fold set with a shallowly plunging, northeasterly-trending fold axis lying in an axial plane with an orientation of N35°E 60°NW. Elements of the first folds are refolded by second-phase folds which have northwesterly striking, near-vertical axial planes. Orientations of modeled P2 fold axes are variable and dependent on the initial attitude of P1 fold elements.

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