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

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. The Alaskan mainland is located at the western end of the North American plate. This region is adjacent to the Bering Sea to the west and overlies the subducting Pacific Plate to the south. The Yakutat microplate subducts northward below Alaska with a velocity similar to that of the Pacific plate but with a lower angle. Many volcanoes have developed in south-central Alaska, including those in the Aleutian arc, the Buzzard Creek-Jumbo Dome, and the Wrangell volcanic field (WVF). However, the origins, storage and transport patterns of the magmas feeding these volcanoes are still unclear and under debate. In this study, we conduct Lg-wave attenuation tomography on the Alaskan mainland and use the results to investigate the regional crustal thermal structure. The imaging results reveal a cold Yakutat terrane and hot crustal features beneath the volcanoes. The Denali volcanic gap is characterized by weak crustal attenuation, indicating that cool crust may have inhibited volcanic activity. Quarter-toroidal crustal melting is revealed by a curved belt of strong attenuation. The crustal magmatic chambers may weakly connect the WVF and the Buzzard Creek-Jumbo Dome volcanoes. A high-resolution broadband Lg-wave attenuation model is obtained for the Alaskan mainland Strong Lg-wave attenuation beneath the volcanoes indicates crustal thermal anomalies and melting A quarter-toroidal crustal melting belt weakly connects the magmatic chambers beneath the Buzzard Creek-Jumbo Dome and Wrangell volcanoes