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Shear Wave Splitting Characteristics of Aligned Partial Melt Configurations in a Subduction Zone Back-Arc Setting

Description: 

Patterns of XKS shear-wave splitting (SWS), which depict the spatial distribution of fast orientation, ϕ, and delay time, δt, are commonly interpreted in terms of upper mantle deformation that causes lattice-preferred orientation (LPO) of anisotropic minerals such as olivine. However, shape-preferred orientation (SPO) of elastically distinct materials may influence SWS observations as well. Building on previous work (e.g., Hammond and Kendall, 2016), we have carried out global wavefield simulations using AxiSEM3D to understand the effects of vertically aligned melt discs (an endmember geometry) on anisotropy observations. We confirm earlier findings that the amount of splitting depends on aspect ratio, melt fraction, and thickness of the inclusion, and indicate the potential of this configuration to crucially influence the strength of observed SWS measurements in a setting where partial melt is present. We explore whether melt SPO along with LPO of olivine might be able to explain the enigmatic occurrence of exceptionally high δt in the High Lava Plains in the Cascadia subduction zone backarc. Here, we expand our modeling efforts to examine splitting due to the presence of dike-like partial melt inclusions, investigating spatial changes in the backazimuthal variation of SWS parameters. We carry out more advanced LPO/SPO models that e.g., invoke dehydration-related olivine fabric transitions in the matrix surrounding the partial melt, which we plan to integrate into generic subduction zone anisotropy models, including those whose geometry captures that of the Cascadia subduction zone.

Session: Anisotropy Across Scales [Poster Session]

Type: Poster

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Eric

Student Presenter: No

Invited Presentation: 

Authors