09:30 〜 09:45
[SCG56-03] Central Japan as a cold subduction zone revisited: implications for deep dehydration beneath the Noto peninsula
キーワード：日本列島、中部日本、沈み込み、脱水、流体、能登半島
The Japan arc consists of several arc segments with different subduction materials and thermal parameters of Pacific Plate (PAP) and Philippine Sea Plate (PSP). Central Japan is a junction of such different segments, beneath which the subducting PAP and PSP slabs overlap. This overlap causes a geological environment specific to this area, including cold mantle wedge and deep dehydration of the slab (Iwamori, 2000; 2007; Nakamura et al., 2008; Nakamura and Iwamori, 2013).
In this presentation, we re-examine the regional distribution of geochemical composition of the erupted lavas over the Japan arc and characterize the magma generation conditions and its spatial (particularly along-arc) variation, through which the physico-chemical condition beneath Central Japan is highlighted. We first utilize the isotopic compositions (Sr-Nd-Pb isotopic ratios) of lavas and statistically analyze them to clarify the geographical provenance. Then we incorporate trace element compositions to discuss source mantle characters, fluid regimes, and degree of partial melting. The results confirm the cold environment beneath Central Japan and suggest a deep dehydration at ~300 km depth from the subducted slab without causing melting above the deep dehydration region, such as the Noto peninsula. The deep dehydration with no melting may account for the earthquake swarm and crustal deformation that suggest a supply of large amount of deep-seated fluid beneath the peninsula (e.g., Nishimura et al., 2022).
In this presentation, we re-examine the regional distribution of geochemical composition of the erupted lavas over the Japan arc and characterize the magma generation conditions and its spatial (particularly along-arc) variation, through which the physico-chemical condition beneath Central Japan is highlighted. We first utilize the isotopic compositions (Sr-Nd-Pb isotopic ratios) of lavas and statistically analyze them to clarify the geographical provenance. Then we incorporate trace element compositions to discuss source mantle characters, fluid regimes, and degree of partial melting. The results confirm the cold environment beneath Central Japan and suggest a deep dehydration at ~300 km depth from the subducted slab without causing melting above the deep dehydration region, such as the Noto peninsula. The deep dehydration with no melting may account for the earthquake swarm and crustal deformation that suggest a supply of large amount of deep-seated fluid beneath the peninsula (e.g., Nishimura et al., 2022).