Abstract

The late Cenozoic Wrangell volcanic belt records a transition in magma supply and geochemistry from a subduction to transform margin between the northeastern Pacific and North American plates. The northwestern volcanic belt comprises calc-alkaline lavas that are above the Wrangell-Wadati Benioff zone, whereas the southeastern belt comprises transitional lavas with minor alkaline and calc-alkaline lavas that overlie a leaky transform fault. The subduction-transform transition is marked by an increase in Fe/Mg and Nb/La ratios and a decrease in Ba/La ratios. Thus, the lavas of the transform regime display a geochemical signature that is intermediate to that of calc-alkaline and intraplate alkaline lavas. Whereas the effects of crustal contamination can be recognized in the evolved lavas of all suites, all primitive lavas in the transform regime are mantle derived and reflect the variable melting and mixing of depleted (mid-ocean ridge basalt) upper mantle, enriched mantle (ocean island basalt), and slab-derived components.

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