Peter Kevin Holmes HBSc thesis abstract

The structure of the Archean metasedimentary rocks of the Beardmore-Geraldton fold belt is investigated.  It has been suggested that two deformational episodes have affected the area near Geraldton.  The F₁ folds are recumbent and not seen in outcrop.  An early foliation (S₁) is observed in thin section that closely parallels bedding (S_o).  The dominant folds of the area, called F₂, have associated an axial-planar, penetrative cleavage (S₂).  This S₂ fabric element is subvertical and generally strikes east-west.

The structural facing direction of F₂ folds is either upward to the west or downward to the east.  Folds with consistent facing directions are separated by an east-west trending shear zone.

Modification of F₂ flexure folds by homogeneous compressive strain, has flattened folds so that they approach the geometry of similar fold styles.  Further modification of fold geometry has occurred due to shear displacements that are typical of the fold belt.  The zone of intense shearing shows how earlier fabric elements have been transposed into the S₂ foliation.

The horizontal compressive forces acting from the north and south have produced the east-west trending shear zone and folds of the area.  These crustal forces have affected the well-stratified metasedimentary rocks and are reflected by the structure, observed on all scales.