Water transportation through the Philippine Sea slab subducting beneath the central Kyushu region, Japan, as derived from receiver function analyses

Abstract

Receiver function analyses are performed to detect seismic velocity discontinuities in the uppermost mantle beneath the Kyushu subduction zone, Japan. The Philippine Sea slab subducting beneath Kyushu is young (26–50 Ma) and steeply dipping (at greater than 30°). We detect a seismic velocity contrast larger than 10% corresponding to the oceanic Moho down to 90 km in depth, implying that the subducting oceanic crust contains more than 3.0 wt.% water down to this depth. We also detect a discontinuity with downward decreasing seismic velocity at depths of 50–80 km, which is parallel to the oceanic Moho and 10 km shallower than it. This fact indicates that there is a sharp discontinuity between the mantle wedge and the hydrous oceanic crust. The existence of such a sharp discontinuity would require a large temperature gradient around the boundary or a permeability barrier at the upper boundary of the slab. We delineate the continental Moho with downward decreasing seismic velocity and the upper boundary of the slab with upward decreasing seismic velocity beneath the forearc region, which implies the existence of serpentinite and/or free fluid which causes high pore pressure in the forearc mantle.

Non-volcanic seismic swarm and fluid transportation driven by subduction of the Philippine Sea slab beneath the Kii Peninsula, Japan

“…Based on a calculated thermal structure in the Kii Peninsula (Yoshioka et al 2009), the conversion from oceanic basalt to eclogite at depths of 40 to 50 km is taking place at approximately 500°C. Similar transitions in receiver function polarities due to the conversion from oceanic basalt to eclogite have been recognized in the Cascadia subduction zone (Abers et al 2009) and Kyushu region (Abe et al 2011).…”

Experimental constraints on the serpentinization rate of fore‐arc peridotites: Implications for the upwelling condition of the slab‐derived fluid

“…The hydration reaction rate of peridotites is a fundamental control of water circulation in subduction zones. Seismic observations of subduction zones in which slab dehydration in fore‐arcs is considerable (i.e., relatively hot subduction zones) have suggested extensive but heterogeneous serpentinization of the fore‐arc mantle wedge, known as “inverted Moho” or low‐velocity anomalies [ Bostock et al ., ; DeShon and Schwartz , ; Abe et al ., ; Kato et al ., ]. Wada et al .…”

“…The hydration reaction rate of peridotites is a fundamental control of water circulation in subduction zones. Seismic observations of subduction zones in which slab dehydration in fore-arcs is considerable (i.e., relatively hot subduction zones) have suggested extensive but heterogeneous serpentinization of the fore-arc mantle wedge, known as ''inverted Moho'' or low-velocity anomalies [Bostock et al, 2002;DeShon and Schwartz, 2004;Abe et al, 2011;Kato et al, 2014]. Wada et al [2008] proposed that the decoupled interface between the subducting slab and the overriding mantle results in a stagnant fore-arc mantle wedge with serpentine-stable conditions; thus, subduction of warm slabs that release abundant H 2 O in the fore arc leads to a high degree of mantle wedge serpentinization.…”

Fluid upwelling beneath arc volcanoes above the subducting Philippine Sea Plate: Evidence from regional electrical resistivity structure

“…‘AF’ and ‘PM’ indicate aqueous fluids released from the subducting slab and partial melting, respectively. ‘ST’, ‘OM’, and ‘CM’ represent the slab top, oceanic Moho, and continental Moho, respectively [e.g., Abe et al , 2011]. ‘VF’ is the volcanic front.…”