Abstract
Multistage plate subduction plays a crucial role in magmatism; however, the mechanisms by which deep geodynamic processes govern volcanism in the Alaska subduction zone remain controversial. In this study, we revealed that the Pacific Plate transitioned from oblique subduction along the Aleutian volcano chain to lower-angle subduction beneath the Pacific-Yakutat Plate interaction zone, forming two slab tears that enhance hot asthenosphere materials upwelling. The partial melting of the mantle wedge induced by Pacific slab dehydration and, the concurrent upwelling of mantle materials, jointly drove volcanism in the transition zone. However, the flat subduction of the Yakutat slab into the mantle wedge overlying the Pacific slab effectively hindered the upwelling of hot hybrid materials, cooling the Pacific mantle wedge. This process produced a non-volcanic gap beneath Denali, reducing volcanic degassing. The findings provide novel perspectives on understanding the volcanic activities in Alaska and their influence on the carbon cycle.