Crustal inheritance and a top-down control on arc magmatism at Mount St Helens

Bedrosian, Paul A.; Peacock, Jared; Bowles-martinez, E.; Schultz, Adam; Hill, G. J.

doi:10.1038/s41561-018-0217-2

Cited by 85 publications

(95 citation statements)

References 33 publications

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“…For example, joint consideration of the velocity and attenuation models of Mt. Saint Helen has provided evidence of magmatic sources located below a thick layer of sediments (Bedrosian et al, ; De Siena et al, ), which is similar to our case. In another case of the Lunayyir basaltic field in Saudi Arabia, the attenuation tomography by Sychev et al () has revealed the traces of degassing in the upper crust, which were not detectable in the seismic velocity model (Koulakov et al, ).…”

Section: Discussionsupporting

confidence: 80%

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

et al. 2019

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We present the results of tomographic studies using seismic velocity and attenuation in the area of the Colima Volcanic complex (CVC). Our dataset comprises body waves from local earthquakes recorded by the temporary seismic stations of the CODEX network in the Colima area and a few stations of the regional Mapping the Rivera Subduction Zone (MARS) networks, both deployed in 2006–2008. We obtain three‐dimensional distributions of seismic velocities and attenuation in the crust beneath the CVC area. At shallow depths, we observe a large negative anomaly to the south of CVC, coinciding with the location of the Central Colima Graben. This anomaly may represent debris avalanche deposits, as well as shallow magma reservoirs feeding the eruptions of the presently active Volcán de Colima. In contrast, the volcano edifice of Nevado de Colima, which is built of rigid igneous rocks, is associated with high‐velocity and low‐attenuation anomalies at shallow depths. In the deeper section, a major anomaly with high Vp/Vs, low Vs, and high S wave attenuation corresponds to the location of the regional Tamazula fault. As this represents a mechanically weakened zone of the crust, it may form the pathway that feeds CVC. Both velocity and attenuation models show that the fault‐associated conduit brought magma from the mantle through the lower crust to a depth of 15 km. Then, a light fraction of magma may continue to ascend, forming shallow reservoirs beneath the southern flank of CVC.

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Section: Discussionsupporting

confidence: 80%

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

et al. 2019

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“…Lower Vs (3.5–3.65 km/s) is imaged at 15‐ to 30‐km depths in much of the 50‐km‐wide region between MSH and Mount Adams (Figures c and g). The distribution of this feature correlates at 30‐km depth with the Southern Washington Cascades Conductor (Bedrosian et al, ; Hill et al, ; Stanley et al, ) and partly correlates at 20‐km depth. Low P wave velocities here are also seen in active‐source imaging (Kiser et al, ).…”

Section: Resultsmentioning

confidence: 90%

“…Wang et al () used ambient noise methodologies to image low velocities in the upper 6 km near the MSH edifice, using a small‐aperture high‐frequency Nodal array concentrated within 15 km of the MSH summit. Regional studies give hints of a region of partial melt in southwestern Washington between MSH, Mount Adams, and Mount Rainier from active‐source seismology (Kiser et al, ), magnetotelluric imaging (Bedrosian et al, ; Hill et al, ), and regional ambient noise tomography (Flinders & Shen, ). Although the locations and shapes of the low‐velocity/high‐conductivity anomalies vary between studies, most indicate an anomalous region of lower crust east of MSH.…”

Section: Tectonic Overviewmentioning

confidence: 99%

“…The iMUSH broadband array (e.g., Mann et al, ) has 70 seismometers spaced every 10 km within 50 km of the MSH edifice, providing the highest‐resolution three‐dimensional (3‐D) images of deep structure beneath MSH, and perhaps any arc volcano, to date. The broadband array complements iMUSH active‐source seismic and magnetotelluric imaging (Bedrosian et al, ; Kiser et al, ). Here, we measure Rayleigh wave phase velocities from ambient noise and integrate those observations with earthquake‐based surface‐wave phase velocities from a parallel study (Janiszewski et al, ).…”

Section: Introductionmentioning

confidence: 99%

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Shear Velocity Structure From Ambient Noise and Teleseismic Surface Wave Tomography in the Cascades Around Mount St. Helens

et al. 2019

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Mount St. Helens (MSH) lies in the forearc of the Cascades where conditions should be too cold for volcanism. To better understand thermal conditions and magma pathways beneath MSH, data from a dense broadband array are used to produce high‐resolution tomographic images of the crust and upper mantle. Rayleigh‐wave phase‐velocity maps and three‐dimensional images of shear velocity (Vs), generated from ambient noise and earthquake surface waves, show that west of MSH the middle‐lower crust is anomalously fast (3.95 ± 0.1 km/s), overlying an anomalously slow uppermost mantle (4.0–4.2 km/s). This combination renders the forearc Moho weak to invisible, with crustal velocity variations being a primary cause; fast crust is necessary to explain the absent Moho. Comparison with predicted rock velocities indicates that the fast crust likely consists of gabbros and basalts of the Siletzia terrane, an accreted oceanic plateau. East of MSH where magmatism is abundant, middle‐lower crust Vs is low (3.45–3.6 km/s), consistent with hot and potentially partly molten crust of more intermediate to felsic composition. This crust overlies mantle with more typical wave speeds, producing a strong Moho. The sharp boundary in crust and mantle Vs within a few kilometers of the MSH edifice correlates with a sharp boundary from low heat flow in the forearc to high arc heat flow and demonstrates that the crustal terrane boundary here couples with thermal structure to focus lateral melt transport from the lower crust westward to arc volcanoes.

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“…Alternatively, the forearc magma may originate farther into the backarc (Bedrosian et al, 2018). The Quaternary basaltic vents occur at the latitude of the~17-Ma Columbia River flood basalts (Camp & Ross, 2004), which, although originating much farther east, represent a significant thermal perturbation to the subduction system that could still be disrupting the slab at greater depth (Obrebski et al, 2010).…”

Section: Slab Continuity and The Search For Magma Originsmentioning

confidence: 99%

Imaging Subduction Beneath Mount St. Helens: Implications for Slab Dehydration and Magma Transport

Mann

Abers

Crosbie

et al. 2019

Geophysical Research Letters

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Mount St. Helens (MSH) is anomalously 35–50 km trenchward of the main Cascade arc. To elucidate the source of this anomalous forearc volcanism, the teleseismic‐scattered wavefield is used to image beneath MSH with a dense broadband seismic array. Two‐dimensional migration shows the subducting Juan de Fuca crust to at least 80‐km depth, with its surface only 68 ± 2 km deep beneath MSH. Migration and three‐dimensional stacking reveal a clear upper‐plate Moho east of MSH that disappears west of it. This disappearance is a result of both hydration of the mantle wedge and a westward change in overlying crust. Migration images also show that the subducting plate continues without break along strike. Combined with low temperatures inferred for the mantle wedge, this geometry greatly limits possible source regions for mantle melts that contribute to MSH magmas and requires lateral migration over large distances.

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Crustal inheritance and a top-down control on arc magmatism at Mount St Helens

Cited by 85 publications

References 33 publications

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

Fault‐Associated Magma Conduits Beneath Volcán de Colima Revealed by Seismic Velocity and Attenuation Tomography Studies

Shear Velocity Structure From Ambient Noise and Teleseismic Surface Wave Tomography in the Cascades Around Mount St. Helens

Imaging Subduction Beneath Mount St. Helens: Implications for Slab Dehydration and Magma Transport

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