Geochemical evidence for an east-dipping Appalachian subduction zone in Newfoundland

Abstract

THE concept of plate tectonics explains the present behaviour of the Earth better than any rival hypothesis. Modern plate motion can be observed and measured, but unfortunately much of the evidence is ephemeral. Spreading ridges, trenches, oceanic magnetic lineaments, zones of seismic activity dipping under erogenic belts, and areas of anomalous heat flow are all destroyed or decay as the plate regime evolves. Applicability of the plate tectonic concept to the ancient past must therefore be determined by more indirect geological observations which are often open to more than one interpretation. For example, it can be inferred that melanges should develop in trenches associated with subduction1, but not all melanges originate in this way arid there is presently no easy way of typefying melanges. Thus, if the great variety of presently observed plate interactions existed in the past, geologic data may not be subtle enough to distinguish them and the record may be blurred beyond reasonable interpretation.