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Seismic imaging shows a melt fraction of up to 20% in the depth range that supplied prior Yellowstone eruptions. 

The Cenozoic Colorado Plateau physiographic province overlies multiple Precambrian provinces. Its ∼2-km elevation rim surrounds an ∼1.6-km elevation core that is underlain by thicker crust and lithospheric mantle, with a sharp structural transition ∼100 km concentrically inboard of the physiographic boundary on all but its northeastern margin. The region was uplifted in three episodes: ∼70–50 Ma uplift above sea level driven by flat-slab subduction; ∼38–23 Ma uplift associated with voluminous regional magmatism and slab removal, and less than 20 Ma uplift associated with inboard propagation of basaltic magmatism that tracked convective erosion of the lithospheric core. Neogene uplift helped integrate the Colorado River from the Rockies at 11 Ma to the Gulf of California by ∼5 Ma. The sharp rim-to-core transition defined by geological and geophysical data sets suggests a young transient plateau that is uplifting as it shrinks to merge with surrounding regions of postorogenic extension. ▪ The Colorado Plateau's iconic landscapes were shaped during its 70-million-year, still-enigmatic, tectonic evolution characterized by uplift and erosion. ▪ Uplift of the Colorado Plateau from sea level took place in three episodes, the youngest of which has been ongoing for the past 20 million years. ▪ Tectonism across the Colorado Plateau's nearest plate margin (the base of the plate!) is driving uplift and volcanism and enhancing its rugged landscapes. ▪ The bowl-shaped Colorado Plateau province is defined by ongoing uplift and an inboard sweep of magmatism around its margins. ▪ The keel of the Colorado Plateau is being thinned as the North American plate moves southwest through the underlying asthenosphere. 

The mantle transition zone connects two major layers of Earth’s interior that may be compositionally distinct: the upper mantle and the lower mantle. Wadsleyite is a major mineral in the upper mantle transition zone. Here, we measure the single-crystal elastic properties of hydrous Fe-bearing wadsleyite at high pressure-temperature conditions by Brillouin spectroscopy. Our results are then used to model the global distribution of wadsleyite proportion, temperature, and water content in the upper mantle transition zone by integrating mineral physics data with global seismic observations. Our models show that the upper mantle transition zone near subducted slabs is relatively cold, enriched in wadsleyite, and slightly more hydrated compared to regions where plumes are expected. This study provides direct evidence for the thermochemical heterogeneities in the upper mantle transition zone which is important for understanding the material exchange processes between the upper and lower mantle.

 

Volcanic arcs consist of many distinct vents that are ultimately fueled by the common melting processes in the subduction zone mantle wedge. Seismic imaging of crustal‐scale magmatic systems can provide insight into how melt is organized in the deep crust and eventually focused beneath distinct vents as it ascends and evolves. Here, we investigate the crustal‐scale structure beneath a section of the Cascades arc spanning four major stratovolcanoes: Mt. Hood, Mt. St. Helens (MSH), Mt. Adams (MA), and Mt. Rainier, based on ambient noise data from 234 seismographs. Simultaneous inversion of Rayleigh and Love wave dispersion constrains the isotropic shear velocity (Vs) and identifies radially anisotropic structures. IsotropicVsshows two sub‐parallel low‐Vszones (∼3.45–3.55 km/s) at ∼15–30 km depth with one connecting Mt. Rainier to MA, and another connecting MSH to Mt. Hood, which are interpreted as deep crustal magma reservoirs containing up to ∼2.5%–6% melt, assuming near‐equilibrium melt geometry. Negative radial anisotropy, from vertical fractures like dikes, is prevalent in this part of the Cascadia, but is interrupted by positive radial anisotropy, from subhorizontal features like sills, extending vertically beneath MA and Mt. Rainier at ∼10–30 km depth and weaker and west‐dipping positive anisotropy beneath MSH. The positive anisotropy regions are adjacent to rather than co‐located with the isotropic low‐Vsanomalies. Ascending melt that stalled and mostly crystallized in sills with possible compositional differences from the country rock may explain the near‐averageVsand positive radial anisotropy adjacent to the active deep crustal magma reservoirs.

 

We conduct a high‐resolution teleseismic receiver function investigation of the subducting plate interface within the Alaskan forearc beneath Kodiak Island using data collected as part of the Alaska Amphibious Community Seismic Experiment in 2019. The Kodiak node array consisted of 398 nodal geophones deployed at ∼200–300 m spacing on northeastern Kodiak Island within the southern asperity of the 1964 Mw9.2 Great Alaska earthquake. Receiver function images at frequencies of 1.2 and 2.4 Hz show a coherent, slightly dipping velocity increase at ∼30–40 km depth consistent with the expected slab Moho. In contrast to studies within the northern asperity of the 1964 rupture, we find no evidence for a prominent low‐velocity layer above the slab Moho thick enough to be resolved by upgoing P‐to‐S conversions. These results support evidence from seismicity and geodetic strain suggesting that the 1964 rupture connected northern (Kenai) and southern (Kodiak) asperities with different plate interface properties.