Compression and crustal shortening in Andean-type orogenesis

CONTROVERSY exists as to the role of crustal compression and shortening in the formation of the easterly-directed thrust system in eastern portions of the North American Cordilleran orogen1,2. In fact, the controversy can be extended to the general issue of the presence or absence of crustal shortening in any major phase of the development of that orogen. Opponents of crustal shortening have suggested that most fold and thrust structures of the Cordilleran orogen can be explained by gravity-induced stresses3,4.