ND AND SR ISOTOPIC CHARACTERIZATION OF THE WRANGELLIA TERRANE AND IMPLICATIONS FOR CRUSTAL GROWTH OF THE CANADIAN CORDILLERA

Nd and Sr isotopic data are reported from samples of most of the major lithologic units of the Wrangellia terrane exposed on Vancouver Island and the Queen Charlotte Islands. Initial εNd values range from +1.0 to +7.3 and initial 87Sr/86Sr ratios range from 0.70323 to 0.70481. These ratios are similar to those of modern island arcs and demonstrate the unevolved, juvenile nature of this terrane. These data indicate that Wrangellia probably resided in an intra-oceanic environment until its accretion to North America. Early Proterozoic crustal components cannot comprise more than about 6% of Wrangellia; therefore the terrane consists of ~94% new, mantle-derived crust. The amount of new crust in Wrangellia is very similar to the amount determined for two other large Cordilleran terranes, Alexander and Stikine. The accretion of juvenile terranes to a continent appears to be an important mechanism of crustal growth. -from Authors