New Insights Into Lithospheric Structure and Melting Beneath the Colorado Plateau

Abstract

The Colorado Plateau and its surroundings serve as an archetypal case to investigate the interaction of mantle melting processes and lithospheric structure. It has been hypothesized that widespread Cenozoic volcanism indicates the encroachment of the convective upwelling of asthenosphere toward the Plateau center. In this study, we generate a Common Conversion Point (CCP) stack of S‐to‐p (Sp) receiver functions to image the locations of lithospheric discontinuities in the southwestern United States. Our results are broadly similar to prior work, showing a strong and continuous Negative Velocity Gradient (NVG) consistent with the Lithosphere‐Asthenosphere Boundary (LAB) over much of the study area. However, with several methodological improvements, we are able to obtain more reliable NVG depth picks below the Colorado Plateau where the LAB becomes weaker, deeper, and broader. We compare the inferred topography of NVGs with the locations of volcanoes, and find that the majority of recent volcanoes are co‐located with lithosphere that is ∼80 km thick. This appears to be the critical depth at which partial melt from upwelling asthenosphere pooling at the base of (or within) the lithosphere may percolate to the surface. We compare our CCP profiles with magma equilibration conditions determined from petrologic analysis and find good agreement between the depth of NVGs and depth of magma equilibration. This analysis provides insight into the progression of magmatism and lithospheric loss toward the center of the Colorado Plateau, and demonstrates how small‐scale processes like melting influence lithosphere‐asthenosphere interactions that persist over large temporal and spatial scales.

Mapping the Lithosphere and Asthenosphere Beneath Alaska With Sp Converted Waves

“…While temperature clearly plays a role in creating high seismic velocities in the mantle lithosphere (Hirth & Kohlstedt, 2003; Stixrude & Lithgow‐Bertelloni, 2005) additional factors have been invoked to produce negative velocity gradients that are vertically localized, including the presence of volatiles and partial melt in the asthenosphere, elastically accommodated grain boundary sliding, near‐solidus weakening, and seismic anisotropy (e.g., L. N. Hansen et al., 2016; Yamauchi & Takei, 2020; also see reviews in Fischer et al., 2020; Karato & Park, 2018; Rychert et al., 2018a, 2018b). In some regions the seismic LAB has been associated with solidi, for example, a relatively dry peridotite solidus in the western U.S. (Golos & Fischer, 2022; Plank & Forsyth, 2016), a hydrated peridotite solidus in subduction zones (e.g., Wang et al., 2020), or a carbonated peridotite solidus beneath the oceans and in subduction zones (e.g., Dasgupta, 2018; Hammouda et al., 2021; Hirschmann, 2010). In Alaska, Rondenay et al.…”

“…accommodated grain boundary sliding, near-solidus weakening, and seismic anisotropy (e.g., L. N. Hansen et al, 2016;Yamauchi & Takei, 2020; also see reviews in Fischer et al, 2020;Karato & Park, 2018;Rychert et al, 2018aRychert et al, , 2018b. In some regions the seismic LAB has been associated with solidi, for example, a relatively dry peridotite solidus in the western U.S. (Golos & Fischer, 2022;Plank & Forsyth, 2016), a hydrated peridotite solidus in subduction zones (e.g., Wang et al, 2020), or a carbonated peridotite solidus beneath the oceans and in subduction zones (e.g., Dasgupta, 2018;Hammouda et al, 2021;Hirschmann, 2010). In Alaska, Rondenay et al (2010) imaged a negative velocity gradient at depths of ∼60 km which they attributed to partial melt pooled beneath the base of the North American lithosphere.…”

A Taxonomy of Upper‐Mantle Stratification in the US

“…Based on our new constraints we re‐evaluate the different models proposed to explain intra‐lithosphere and transitional discontinuities (Karato & Park, 2018; H. Yuan & Romanowicz, 2018). They include partial melting (Golos & Fischer, 2022; Hua et al., 2023; Rader et al., 2015) chemical stratification or metasomatism (Krueger et al., 2021; T. Liu et al., 2023; Rader et al., 2015; Saha et al., 2021; Selway et al., 2015), variable anisotropy (Wirth & Long, 2014; H. Yuan & Levin, 2014; H. Yuan & Romanowicz, 2010), and elastically accommodated grain‐boundary sliding (Karato et al., 2015). Many of these models were proposed shortly after the early detection of lithosphere discontinuities when a detailed view of upper mantle stratification was unavailable.…”

“…Yuan & Romanowicz, 2018). They include partial melting (Golos & Fischer, 2022;Hua et al, 2023;Rader et al, 2015) chemical stratification or metasomatism (Krueger et al, 2021;T. Liu et al, 2023;Rader et al, 2015;Saha et al, 2021;Selway et al, 2015), variable anisotropy (Wirth & Long, 2014;H.…”

A Taxonomy of Upper-Mantle Stratification in the US

“…Yuan & Romanowicz, 2018). They include partial melting (Hua et al, 2023;Rader et al, 2015;Golos & Fischer, 2022) chemical stratification or metasomatism (Krueger et al, 2021;T. Liu et al, 2023;Rader et al, 2015;Saha et al, 2021;Selway et al, 2015), variable anisotropy (Wirth & Long, 2014;H.…”