Modeling study of the small-scale mantle convection in the subduction zone mantle wedge including the melting mechanism of mantle rocks

Abstract:

It is observed that subduction zone mantle wedge is not uniform even in　the direction along the overlying island-arc that is perpendicular to the subducting direction. The hot fingers model is a hypothetical model specifying the three dimensional structural variation within the mangle wedge; it assumes that there is a fingers-like stripe pattern of mechanical and thermodynamical properties within the wedge. Those non-uniformity appears over the arc crust as nonuniform distribution of volcanic eruptions. Indeed, quaternary volcanoes in the NE Japan arc could be grouped into ten volcano clusters striking transverse to the arc. These have an average width of  50 km, and are separated by parallel gaps 30-75 km wide. Moreover, the structure of the mantle wedge and arc crust beneath the NE Japan arc and the Izu-Bonin-Mariana arc, respectively, suggest that the third dimension, lying along the strike of the arc, is necessary to understand the actual production of magmas in subduction zones. To explore the physical and mathematical mechanism of formation of the hotfingers pattern, we develop a model of mantle convection in the mantle wedge. Our model incorporates the melting mechanism of the mantle rocks, which affect temperature and velocity of mantle. Our model produces a spatiotemporal pattern in those variables. The obtained results are compared with the spatiotemporal patterns observed in the NE Japan arc.