Control of Volcanic Activity by Crustal Structure: Inference from the Izu‐Bonin‐Mariana and Northeast Japan Arcs

Abstract

AbstractVolcanic activities in the Izu‐Bonin‐Mariana (IBM) oceanic arc and the Northeast Japan (NEJ) continental arc are different in spite of rather constant subduction rates of the same Pacific plate. IBM volcanoes are much more voluminous than NEJ volcanoes; IBM magmas are predominantly basaltic whereas NEJ magmas are andesitic. We propose that the crustal density structures play a key role in those differences. The crustal density structures were estimated based on seismic P‐wave velocity structure and thermodynamic calculation, suggesting that the neutral buoyancy level of a primitive, mantle‐derived basalt, where a magma chamber forms, is shallower in the IBM arc than the NEJ arc. If a magma that differentiates and attains water oversaturation could erupt at the surface, a larger amount of crystallization should occur for the magma in a deeper chamber. This idea explains that erupting magma in the IBM arc is more voluminous and more mafic than those in the NEJ magma.