Joint Analysis of Seismic and Electrical Observables Beneath the Central Appalachians Requires Partial Melt in the Upper Mantle

Abstract

Understanding the composition and state of the upper mantle remains a fundamental outstanding problem in the study of the Earth's interior. Variables such as the mineralogy/composition, temperature, water content, and (if present) partial melt fraction and configuration play key roles in controlling upper mantle rheology and dynamics. It is particularly important to understand these variables in regions of the upper mantle that are anomalous or unusual, as such regions are often associated with processes (e.g., intraplate volcanism) that are not predicted by simple plate tectonic theory. However, reliably estimating quantities such as the temperature, water content, and melt fraction in the upper mantle remains an enormous challenge for observational geophysics. While geophysical observables such as seismic velocity, seismic attenuation, and electrical conductivity are sensitive to these quantities, their interpretation is typically non-unique, and the uncertainties in translating laboratory experiments to the real Earth are large. A promising strategy for constraining these variables more tightly in regions of interest is to combine co-located observations of seismic velocity, seismic attenuation, and/or electrical conductivity (e.g.,

Lateral Variations in Teleseismic Attenuation of the Conterminous U.S. and New Insights Derived From Its Relationship to Mantle Seismic Velocity

“…Tectonic activity in the western U.S. (where LAAR is highest) is generally much more recent than in the Appalachians (the other part of the model with high LAAR values), yet magmatic activity in parts of the Appalachians has been documented as recently as the Eocene (e.g., Mazza et al., 2017). High‐amplitude velocity anomalies have been consistently observed in the northern and central Appalachians and the joint interpretation of multiple geophysical constraints favors the presence of melt in at least the central Appalachians (e.g., Mittal et al., 2023).…”