Correlation of Quaternary Volcano Clusters With Partial Melting of Mantle Wedge, Northeast Japan: A Numerical Model Study

Abstract

The Quaternary volcano clusters in Northeast Japan and the no-volcano zones between them imply extensive and scarce melting, respectively, in the mantle wedge, but no quantitative study on the heterogeneous melting has been conducted. Here, we constructed two-dimensional numerical models by considering along-arc temperature variations in the mantle wedge expressed as high-(hot fingers) and low-temperature anomalies (deterred corner flow) with the slab dehydration, porous flow of aqueous fluid, and partial melting of the mantle wedge. The results show that the high-and low-temperature anomalies in the mantle wedge result in extensive and negligible melting beneath the volcano clusters and no-volcano zones, respectively, consistent with geochemical and geophysical estimations. Contrary to the near-complete slab dehydration beneath the volcano clusters, the partially dehydrated subducting slab beneath the no-volcano zones transports the remaining water into the mantle transition zone, which has implications for intraplate volcanoes in Northeast Asia. Plain Language SummaryThe Quaternary volcanoes in Northeast Japan are expressed as 11 volcano groups and are thought to be correlated with localized and extensive partial melting in the mantle wedge beneath these groups. However, scarce melting is expected in the mantle wedge beneath the no-volcano zones between those volcano groups. Because no quantitative study on partial melting in the mantle wedge has been conducted, we carried out two-dimensional numerical modeling by considering the high-and low-temperature anomalies in the mantle wedge beneath Northeast Japan and evaluated the slab dehydration and melting therein. Our results show extensive melting beneath the volcano groups but negligible melting beneath the no-volcano zones; localized high mantle temperatures result in the formation of the volcano groups. The remaining water stored in the hydrous minerals in the subducting slab beneath the no-volcano zones is transported into the mantle transition zone, which has implications for intraplate volcanoes in Northeast Asia.

Role of warm subduction in the seismological properties of the forearc mantle: An example from southwest Japan

“…2D), most of the water finally reaches the overlying crust; only a small amount of free water is thus incorporated in the corner flow and leaves the model domain (Fig. 4) [e.g., (23,30)]. The isotropic permeability of the serpentinite layer (no foliated serpentinite) inhibits fluid flow toward the corner of the mantle wedge (see the Supplementary Materials).…”

“…The top depth transforms the base of the mantle wedge (chlorite-bearing lherzolite) above the fully coupled slab-mantle interface. The base is incorporated into the corner flow and gradually breaks down with depth [e.g., (23,30)]. Model results considering diverse subduction parameters and conditions show that the spontaneous growth of the serpentinite layer toward the corner of the mantle wedge can be observed only when we incorporate the anisotropic permeability of the serpentinite layer for the warm slab (see the Supplementary Materials).…”

“…For the boundary conditions of the solid-state flow, the slab-mantle decoupling zone on the slab surface is prescribed with 5% of the convergence rate for depths from 35 to 70 km, including the linear velocity ramp at a depth of 75 km, consistent with low heat flows of the forearc regions observed in southwest and northeast Japan (53). Below the downdip depth of the decoupling zone at a depth of 75 km, full coupling is applied to the slab surface [e.g., (23,30,54)]. No-slip and open boundary conditions are prescribed on the continental Moho and outer boundaries of the mantle wedge, respectively.…”

“…S1B) [e.g., (23,28) S3. To consider the depth-dependent and localized distribution of mineral-bound water in the subducting slab [e.g., (23,30,54)), 100%, 40%, and 25% hydrations of the three layers are assumed. This indicates that the sediment layer is fully hydrated but the basaltic oceanic crust and underlying lithospheric mantle are partially hydrated; the partial hydration represents the fully hydrated zone (e.g., fault and fracture zones) surrounded by ambient anhydrous (dry) zone (56,58).…”

“…A background mass fraction of 10 −4 (0.01 wt %) is prescribed on the outer boundaries of the mantle wedge for the back-arc mantle (59). No bound-water flux boundaries are prescribed on the other inner and outer boundaries to prevent the artificial diffusion of the mineral-bound water across the layers, mantle wedge, and overlying continental crust [e.g., (23,30)]. For the fluid flow of free water, no free water flux boundary is prescribed on the bottom of the hydrated portion of the subducting slab, and a background volume fraction of free water (10 −4 ) is prescribed on the other open boundaries (fig.…”