[S-IT15] Mass and energy transport properties and processes in the crust and the mantle

[SIT15-P12] Role of the sub-forearc weak hydrous layer in the arc volcanism and nonvolcanic seismic tremor in the Japan subduction zone

*CHANGYEOL LEE¹ (1.Yonsei University)

Keywords:weak hydrous layer, arc volcanism, nonvolcanic seismic tremor, Japan subduction zone

Among the subduction zones around the world, the Japan subduction zone is one of the best natural laboratories because the subduction zone has two end-member varieties: the Southwest and Northeast Japan subduction zones where the young Philippine (~15 Ma) and old Pacific oceanic plate (~130 Ma) sink at the Nankai trough and Japan trench, respectively. The Southwest Japan subduction zone is well known for the present-day rare arc volcanism and along-trench nonvolcanic seismic tremor in the forearc mantle and nearby. Since the subduction initiation at ~17 Ma, the forearc-to-arc volcanic front has been simultaneously migrated, coeval with the volcanism of the mid-Miocene high-magnesium andesite (HMA) (~15–12 Ma), scattered monogenic volcanism (~12–4 Ma), Quaternary adakite volcanism (< ~2 Ma), and rare arc volcanism (present). The numerical model results show that the spontaneous downdip growth of the weak hydrous layer (e.g., serpentinite) at the slab interface converts the hot forearc mantle to cold mantle, explaining the volcanic front migration and the coeval magmatism since the subduction initiation at ~17 Ma. The weak hydrous layer transports most of the expelled fluids from the slab toward the tip of the mantle wedge, explaining the rare arc volcanism owing to weak flux melting in the mantle wedge, the nonvolcanic seismic tremors owing to fluid overpressure and slab/mantle-derived geochemical components in deep groundwater. Compared to the rare arc volcanism and nonvolcanic seismic tremor in the Southwest Japan subduction zone, the Northeast Japan subduction zone has experienced frequent arc volcanism but no nonvolcanic seismic tremor in the forearc mantle. The model results show that most of the fluids expelled from the slab enters the overlying arc and backarc mantle, yielding intensive flux melting; no meaningful amount of the weak hydrous layer forms in the forearc mantle and no transport of the expelled fluids from the slab toward the tip of the mantle wedge occurs. This explains both the frequent arc volcanism and paucity of the nonvolcanic seismic tremor in the forearc mantle.