Structural analysis from air photographs in areas of regionally metamorphosed rocks

Abstract An attempt is made to extend the use of photogeology in areas of regional metamorphism by structural analysis of fold structures at the macroscopic scale. Problems and methods of measuring dip and strike of lithological layering from air photographs are discussed. An experiment in structural analysis using data from air photographs is described for an area of 20 sq. miles west of Chisali, Malawi (Fig. 1). Analyses of two domains and six sub-domains yield data on trend and dip of axial planes, and trend and plunge of fold axes. An analysis is made of a large superimposed fold structure at Mahenge, Tanzania. This structure is the result of three fold movements, the order and nature of which are ascertained. It is concluded that structural analysis by photogeological methods alone provides valid, if limited, information about the style of folding and fold generations, and if applied to very large areas might lead to a correlation of fold systems within one orogenic zone, and to the delineation of adjacent orogenic zones. The method could also be used in areas of folded sedimentary rocks.