Along‐Strike Variations in Sub‐Arc Melting Beneath the Alaska Peninsula Revealed by P‐Wave Attenuation

Abstract

The diverse volcanic activity in the Alaska Peninsula section of the Alaska‐Aleutian subduction zone is presumably caused by substantial variations in mantle wedge melting or trans‐crustal processes beneath the arc. In this study, we investigate sub‐arc melting beneath the Alaska Peninsula by measuring P‐wave attenuation, as attenuation is highly sensitive to temperature and partial melts. Our results reveal high attenuation anomalies with varying intensity and extent in the mantle wedge, together with previously published seismic velocity models, reflecting significant along‐strike variations in mantle wedge melting that are controlled by slab dehydration. The extensive slab dehydration in the Pavlof to the southwest and Chirikof‐Kodiak segments to the northeast promotes significant partial melting in the mantle wedge, whereas the Shumagin‐Chignik segments in the middle have limited slab dehydration and melt generation. However, the along‐arc changes in mantle wedge melting do not correspond well to the variations in volcanic eruption style, eruption frequency, and magma composition at the surface. In contrast, the crustal structure imaged by V _P / V _S tomography changes abruptly across the Becharof discontinuity. These observations suggest that surface volcanism along the Alaska Peninsula is likely modulated by trans‐crustal processes, such as the upper‐crustal stress regime, in addition to mantle magma supply. We also observe strong scattering attenuation in the fore‐arc crust, indicating widespread deformation and cracks in the overriding plate southwest of Chirikof Island.