A deformation partitioning approach to resolving the sequence of fold events and the orientations in which they formed across multiply deformed large-scale regions

Regional distributions of axial plane trends retain information on the orientation in which successive generations formed because multi-scale partitioning results in most orogenic belts preserving subsequently undeformed portions of all large-scale folds. At depths greater than ∼10 km within orogens, successions of regional folds are accompanied by the sequential development of crenulation hinges in pelites, which are commonly overgrown early during their development by successive generations of porphyroblasts. Consequently, the original trends of the axial planes of these folds are preserved within the distribution of foliation inflection/intersection axes within porphyroblasts (FIAs). Peaks in the distribution of FIA trends in western Maine predominantly coincide with peaks in the distribution of trends of the axial planes of macroscopic and regional folds. The WNW–ESE (∼420 Ma), N–S (408 ± 10 Ma), W–E (388 ± 9 Ma), WSW–ENE (372 ± 5 Ma), SW–NE (353 ± 4 Ma) succession of FIA peaks defines the sequence of folds and accords with map scale overprinting relationships. This quantitative approach to interpreting fold successions in multiply deformed terrains resolves timing where overprinting criteria are rare, uncertain or obliterated by younger events in portions of the orogen. Significantly, lengthy detailed histories of structural development can be extracted from a small area containing porphyroblastic rocks and applied to very large-scale regions. ► Zones of porphyroblastic rock preserve the effects of the numerous regional deformation events. ► FIAs are a product of folding events and their trends are controlled by folds with steep axial planes. ► FIA trends directly reflect folds that formed with steeply dipping axial planes. ► Regional fold trends have peaks coincident or within 10° of a succession of FIA peaks. ► FIAs provide the regional successions of folding preserving the orientations in which they formed.