Strong Lg‐Wave Attenuation Reveals Quarter‐Toroidal Crustal Melting Around the Yakutat Terrane in South‐Central Alaska

Abstract South‐central Alaska features a history of massive volcanic activity. How the Denali volcanic gap (DVG) formed and why the Wrangell volcanoes are clustered remain vigorously debated. Investigating the crustal thermal structure can be crucial for understanding subsurface magmatic activity. We present a high‐resolution broadband Lg‐wave attenuation model to constrain crustal thermal anomalies beneath Alaska. Strong Lg attenuation is observed beneath the volcanoes in south‐central Alaska, indicating thermal anomalies and possible melting in the crust. In contrast, the central Yakutat terrane (YT) and DVG are characterized by weak Lg attenuation, suggesting the existence of a cool crust that prevents hot mantle materials from invading the crust. This cool crust is likely the reason for the DVG. Quarter‐toroidal crustal melting with strong attenuation is revealed around the YT. This curved zone of crustal melting, possibly driven by toroidal mantle flow, weakly connects the Wrangell and Buzzard Creek‐Jumbo Dome magmatic chambers.