Seismic Architecture of the Lithosphere-Asthenosphere System in the Western United States from a Joint Inversion of Body- and Surface-wave Observations: Distribution of Partial Melt in the Upper Mantle

This is a Preprint and has not been peer reviewed. The published version of this Preprint is available: https://doi.org/10.26443/seismica.v2i2.272. This is version 1 of this Preprint.

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Authors

Joseph Byrnes , James Gaherty, Emily Hopper

Abstract

Quantitative evaluation of the physical state of the upper mantle, including mapping temperature variations and the possible distribution of partial melt, requires accurately characterizing absolute seismic velocities near seismic discontinuities. We present a joint inversion for absolute but discontinuous models of shear-wave velocity (Vs) using 4 types of data: Rayleigh wave phases velocities, P-to-s receiver functions, S-to-p receiver functions, and Pn velocities. Application to the western United States clarifies where upper mantle discontinuities are lithosphere-asthenosphere boundaries (LAB) or mid-lithospheric discontinuities (MLD). Values of Vs below 4 km/s are observed below the LAB over much of the Basin and Range and below the edges of the Colorado Plateau; the current generation of experimentally based models for shear-wave velocity in the mantle cannot explain such low Vs without invoking the presence of melt. Large gradients of Vs below the LAB also require a gradient in melt-fraction. Nearly all volcanism of Pleistocene or younger age occurred where we infer the presence of melt below the LAB. Only the ultrapotassic Leucite Hills in the Wyoming Craton lie above an MLD. Here, the seismic constraints allow for the melting of phlogopite below the MLD.

DOI

https://doi.org/10.31223/X5PQ0V

Subjects

Earth Sciences, Geophysics and Seismology, Physical Sciences and Mathematics

Keywords

lithosphere-asthenosphere boundary, Seismic tomography

Dates

Published: 2022-11-08 23:17

Last Updated: 2022-11-08 23:17

License

CC BY Attribution 4.0 International

Additional Metadata

Data Availability (Reason not available):
Data is available at the lead author's github, linked in the article, and will get given a persistent link upon publication.