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Publisher-reported update

2026-08-26

In the Wrangell Volcanic Belt (WVB) a northwesterly increase in volume of calc-alkaline versus transitional (sodic alkaline/calc-alkaline) magmatism is accompanied by a migration in the locus of magmatic activity. The space-time-composition relationships reflect oblique convergence between the North American and Pacific plates over the last 17.3 million years. Compositional- temporal trends are particularly well preserved in the four stages of volcanic stratigraphy in the St. Clare Creek field (17.3-6.5 Ma). Initially, alkaline olivine basalts, hawaiites and mugearites were erupted from small, isolated shield volcanoes in the axis of a continental molasse basin. The alkaline lavas were followed by an early stratovolcano stage of transitional trachybasalts and high-Fe basaltic trachyandesites, succeeded by basaltic trachyandesites, trachyandesites, trachytes, rhyolites and rare basaltic andesites. Widespread basaltic fissure eruptions dominated the third volcanic stage. The late stratovolcano stage consisted of renewed eruption of intermediate and felsic transitional lavas. A systematic temporal-chemical relationship between early alkaline and younger transitional and…

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