The Significance and Application of Foliation Intersection/Inflection Axes (FIA( within Porphyroblasts: A review



An increasing number of structural and metamorphic studies throughout the past sixty years have shown the importance of using porphyroblast microstructures to gain further understanding of deformation and metamorphic history and mechanisms. A recent very significant advance has been the development of techniques for the measurement of Foliation Intersection/Inflection Axes (FIAs) preserved within porphyroblasts. FIAs provide a quantitative method of microstructural analysis that enables the tonic history. The FIA technique determines the orientation of or the axis of curvature of a foliation effected by and overprinting event, or the intersection lineation between successive foliations, preserved as inclusion trails within porphyroblasts. Because the axis is determined completely independent of the model of formation of these included foliations, it allows such models to be thoroughly tested. The method involves three-dimensional examination of microstructures within porphyroblasts in several vertically

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