Melt Architecture Under East Asian Volcanoes Revealed by Anisotropic Tomography

Cenozoic volcanic rocks in East Asia are widespread across subduction zones, oceanic plates, and continental interiors. The generation of these volcanic materials is closely associated with partial melting of the upper mantle and the stagnation of the Pacific slab in the mantle transition zone. However, the spatial distribution and migration of melts in the upper mantle remain poorly understood. Here we develop an updated tomographic approach for P-wave tilting-axis anisotropy and apply it to the East Asian region. Our model reveals significant anisotropy in the upper mantle beneath volcanic fields, as well as in the lower mantle underlying the stagnant slab. The anisotropy in the subduction zone is too strong to be caused by only lattice-preferred orientation of peridotite; instead, it can be partly attributed to shape-preferred orientation of elongated/flat pores within melt-rich bands. By examining the hypothesis that the primary mechanism of anisotropy is the alignment of pores filled by melt, we identify a pervasive melt layer at ∼300 km depth beneath East China, with segments rising toward the base of the lithosphere beneath intraplate volcanic centers. Through quantifying the spatial distribution of melt, including its volume fraction and pore aspect ratio, our tomography illustrates the organization and migration of melt in relation to intraplate volcanism. This study emphasizes the significance of the melt pores' shape-preferred orientation in understanding anisotropy in the upper mantle and uppermost lower mantle.