"Seismically anisotropic magma reservoirs underlying two western US supervolcanoes"

Speaker: Chengxin Jiang, post-doc in the Denolle group

Abstract:  A better understanding of the architecture of existing magmatic reservoirs in the crust is of great value for the evaluation of possible volcanic eruptions in the future. While the location and geometry of magmatic low-velocity bodies are frequently constrained by tomographic inversions, less is known about the configuration of melts within reservoirs or pathways connecting reservoirs. Seismic anisotropy can illuminate structural fabrics or layering with length scales too fine to be resolved as distinct features in most seismic tomography. In this study, seismic anisotropic structures were investigated beneath Yellowstone and Long Valley calderas. Significant positive anisotropy and low isotropic velocities were found beneath both calderas at ~5-18 km depths, which are anomalously strong compared to the surrounding areas. We propose that the anisotropic volumes represent sill complexes of compositionally evolved magma, whose seismic contrast with the crust would largely fade upon crystallization. The similarity of magma reservoir anisotropy in varied tectonic settings suggests that such mid-crustal sill complexes may be ubiquitous features of voluminous silicic magmatic systems, and that anisotropy should be considered to seismically estimate melt content and mobility.

Lunch will be provided. As always, please plan to bring reusable plates and cutlery to reduce waste.