Subduction hydrothermal regime and seismotectonic variation along Kermadec–Tonga megathrusts

Abstract

The calamitous phreatomagmatic eruption of the Hunga Tonga–Hunga Ha'apai (HTHH) volcano in January 2022 has been reported to have had a volcanic explosivity index (VEI) of 5-6 and a column height of 20 km and to have caused powerful tsunamis across the Pacific Ocean. Along the subvolcanic heterogeneous and tightly coupled megathrusts, the hydrothermal structure is considered essential to the deep arc volcanism and catalysis of focused interplate earthquakes. However, at present, such heterogeneity in slab hydrothermal regimes and the linkage of slab metamorphism to seismotectonics and magmatism remain poorly understood. Here, based on the recurrence of subduction earthquakes and the obtained surface heat flow estimates as constraints, we constructed a 3D thermodynamic model to study this subduction complex and the seismotectonic variation beneath Kermadec–Tonga. The subduction of the Pacific plate beneath the Kermadec–Tonga microplate is associated with a cold thermal transition from 300 °C to >900 °C on forearc interface. The distribution of seismicity is related to the dehydration of subducted water-bearing minerals which promotes the occurrence of both fast and slow subduction earthquakes. Slab metamorphism released large amounts of fluids, especially those from intraslab harzburgitization, which are key to influencing mantle melting and arc volcanism in Kermadec-Tonga.