Control of slab tears and slab flat wedging on volcanism in the Alaska subduction zone

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. Using numerous travel-time data from several seismic arrays, we constructed high-resolution tomographic models to investigate the velocity structure of the Pacific Plate and Yakutat slab. Our tomographic results revealed high-velocity anomalies in the Pacific Plate and Yakutat slab, while the low-velocity areas within the Pacific Plate were identified as slab tears. We suggest 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. Conversely, 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. These results offer a new perspective on the influence of slab dynamics on volcanic and magmatic processes in the region and represent an advancement in our understanding compared to previous studies, which did not resolve the tears within the slab or their geodynamic implications at this level of detail.