Deep mantle upwellings and their interactions with subducting slabs beneath the Kamchatka–Aleutian–Alaska region

Summary Using more than six million P, pP, and PP travel-time data recorded by global seismic networks, we obtain a new high-resolution whole-mantle P-wave tomography model beneath the Kamchatka–Aleutian–Alaska subduction system. The model clearly delineates the Pacific slab subducting beneath the North America and Okhotsk plates, as well as a remnant of the Kula slab trapped in the mantle transition zone. Distinct low-velocity anomalies are identified both above and below the subducting slabs. The above-slab low-velocity anomalies (ALVAs) are interpreted as corner flow in the mantle wedge associated with the slab dehydration, whereas the sub-slab low-velocity anomalies (SLVAs) represent hot and wet upwelling flows interacting with the descending slabs. In the lower mantle, broad low-velocity zones are imaged beneath the western Aleutian–Kamchatka and the Gulf of Alaska, extending continuously from the core–mantle boundary toward the mantle transition zone. These features suggest that plume-like upwelling flows from the lowermost mantle impinge upon the base of the subducting slabs, forming complex three-dimensional circulation patterns including slab windows and toroidal flow around slab edges. Spatial comparisons indicate that the rupture zones of M9-class megathrust earthquakes are generally located above gaps or terminations of the SLVAs, implying a structural partitioning between deep upwelling zones and strongly coupled seismogenic areas. Beneath the eastern Aleutian arc, remnants of the Kula slab exist in the mantle transition zone, forming a slab window with the overlying Pacific slab. Another slab window exists beneath southern Kamchatka. Great volcanic eruptions tend to occur near slab windows where both ALVAs and SLVAs are well developed. The results provide new insight into how whole-mantle convection, subduction evolution, and surface tectonic processes are dynamically connected beneath one of the most active convergent margins on Earth.