Trace Element Constraints on the Origin of Cordilleran Batholiths

Abstract

The problem of the origin of cordilleran batholiths cannot, because of their immense volume, be separated from the origin of the continental crust itself. Despite arguments as to when and how the crust was generated, the extent of continental reworking and mobilization and the importance of sediment recycling (see Fyfe, 1978, 1979; Brown, this volume), there can be little doubt from isotopic studies (Moorbath, 1977, 1978; McCulloch and Wasserburg, 1978; Hamilton et al., 1979) that large areas of continental crust represent new additions of sialic material from the mantle system at various periods. Tarney (1976) and Windley and Smith (1976) drew attention to the broad compositional similarities between Archaean continental crust and the cordilleran batholiths of North and South America. Tonalite is a dominant component in both — this is particularly so in the more deeply eroded parts of the Andean cordillera, where the plutonic rocks frequently have a distinct fabric and may even be foliated. Whether the crustal generation processes in the Archaean exactly paralleled those in the modern Andes, however, remains to be determined.