The Canadian cordillera as a modern analogue of proterozoic crustal growth

Processes of crustal accretion and the real additions to continental volume occurring in the Canadian Cordillera 0.25 Ga to present are viewed as an analogue for major crustal addition episodes in Proterozoic 2.5-0.5 Ga time. The Canadian Cordillera represents a minimum of 20% (maximum 25%) of the global Phanerozoic crustal growth rate. This is similar to Proterozoic crustal genesis events such as the Grenville Belt and the Arabian-Nubian Shield, but represents less crust production than the 1.9-1.7 Ga events of North America-Greenland-Europe. The Canadian Cordillera is a valid modern analogue for Proterozoic events chiefly on grounds other than crustal quantity, however. These grounds are (1) progressive accretion of terranes to the continent; (2) predominance of arc-related rocks; (3) difficulty of identifying sutures between terranes; (4) high abundance of positive-eNd, hence juvenile rocks; and possibly (5) presence of transcurrent motions leading to accumulation of terranes preferentially along one part of the continental margin. The Canadian Cordillera represents a qualitative equivalent of Proterozoic orogenic belts, and is one in which stratigraphic, structural and major tectonic relations can often be discerned due to palaeontological and palaeomagnetic control, low metamorphic grade and limited extent of melting and granitoid intrusion. The Canadian Cordillera may thus serve as a natural laboratory for Proterozoic events, where palaeontological and palaeomagnetic control are not available, metamorphic grade is high, stratigraphy often only decipherable to a limited extent and melting and granitoid intrusion are widespread. The more sophisticated interpretation of Nd, Sr and Pb isotopic data that is possible in the Cordillera because of the other controls-may be fed back into Proterozoic situations where those controls are not available.