Seismic Constraints on a Double‐Layered Asymmetric Whole‐Mantle Plume Beneath Hawai‘i

Cheng, Cheng; Allen, R. M.; Porritt, R. W.; Ballmer, Maxim D.

doi:10.1002/9781118872079.ch2

Cited by 21 publications

(44 citation statements)

References 88 publications

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“…Anelasticity might result in higher seismic velocity reduction for a given temperature anomaly (Jackson & Faul, 2010), in particular for long period waves, since the velocity reduction is proportional to the integral of the attenuation at all frequencies above the considered frequency (Takei, 2017). This could explain, for instance, that tomographic models based solely on surface waves data (Laske et al, 2011) image stronger velocity anomalies than those combining multiple data types (Cheng et al, 2015). However, at temperatures below 1200°C, anelasticity effects should be small (Takei, 2017).…”

Section: Discussionmentioning

confidence: 99%

“…Surface wave and multiphase tomography models portray reduced seismic velocities (by up to −3%) in the lithospheric mantle within 150 km from the volcanic chain (Figure 1) (Cheng et al, 2015; Laske et al, 2011). However, the weak heat flow anomaly in the swell implies modest heating (100–200°C) confined to the base of the lithosphere (Von Herzen et al, 1989).…”

Section: Introductionmentioning

confidence: 99%

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Textural and Compositional Changes in the Lithospheric Mantle Atop the Hawaiian Plume: Consequences for Seismic Properties

Tommasi

Mameri

Godard

2020

Geochem Geophys Geosyst

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We characterized the texture, composition, and seismic properties of the lithospheric mantle atop the Hawaiian plume by petrostructural analysis of 48 spinel peridotite xenoliths from four localities in three Hawaiian islands. Coarse‐porphyroclastic peridotites with variable degrees of recrystallization, recorded by growth of strain‐free neoblasts onto the deformed microstructure, predominate. Full evolution of this process produced equigranular microstructures. Some peridotites have coarse‐granular microstructures. Coarse‐granular and coarse‐porphyroclastic peridotites have strong orthorhombic or axial‐[100] olivine crystal‐preferred orientations (CPOs). Recrystallization produced some dispersion and, locally, changed the olivine CPO towards axial‐[010]. Enrichment in pyroxenes relative to model melting trends and pyroxenes with interstitial shapes and CPO uncorrelated with the olivine CPO imply refertilization by reactive melt percolation. The unusual spatial distribution of the recrystallized fraction, Ti enrichment, and Rare Earth Element fractionation in recrystallized, equigranular, and coarse‐granular peridotites support that these microstructures are produced by static recrystallization triggered by melt percolation. However, there is no simple relation between microstructure and chemical or modal composition. This, together with marked variations in mineral chemistry among samples, implies multiple spatially heterogeneous melt‐rock reaction events. We interpret the coarse‐porphyroclastic microstructures and CPO as representative of the original oceanic lithosphere fabric. Annealing changed the microstructure to coarse‐granular, but did not modify significantly the olivine CPO. Recrystallization produced moderate dispersion of the CPO. “Normal” oceanic lithosphere seismic anisotropy patterns are therefore preserved. Yet Fe enrichment, refertilization, and limited heating of the base of the lithosphere may reduce seismic velocities by up to 2%, partially explaining negative velocity anomalies imaged at lithospheric depths beneath Hawaii.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Textural and Compositional Changes in the Lithospheric Mantle Atop the Hawaiian Plume: Consequences for Seismic Properties

Tommasi

Mameri

Godard

2020

Geochem Geophys Geosyst

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“…In the EGFs, we note the presence of a low‐velocity wave traveling behind the Rayleigh wave (Figure S5). The trailing arrival is due to the water column above the ocean bottom stations [e.g., Cheng et al , ]. The asymmetrical nature of the water waves in the EGFs can be attributed to an asymmetrical distribution of noise sources due to the stations' location along the coast.…”

Section: Methodsmentioning

confidence: 99%

Crustal structure across the eastern North American margin from ambient noise tomography

Lynner

Porritt

2017

Geophysical Research Letters

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Passive tectonic margins, like the eastern North American margin (ENAM), represent the meeting of oceanic and continental material where no active deformation is occurring. The recent ENAM Community Seismic Experiment provides an opportunity to examine the crustal structure across the ENAM owing to the simultaneous deployment of offshore and onshore seismic instrumentation. Using Rayleigh wave phase and group velocities derived from ambient noise data, we invert for shear velocity across the ENAM. We observe a region of transitional crustal thicknesses that connects the oceanic and continental crusts. Associated with the transitional crust is a localized positive gravitational anomaly. Farther east, the East Coast magnetic anomaly (ECMA) is located at the intersection of the transitional and oceanic crusts. We propose that underplating of dense magmatic material along the bottom of the transitional crust is responsible for the gravitational anomaly and that the ECMA demarks the location of initial oceanic crustal formation.

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“…Whole‐mantle tomography is increasingly capable of resolving low‐velocity features that confirm the hypotheses of ascending plumes from the core‐mantle boundary, matched with locations of major midplate volcanism (French & Romanowicz, ). In the case of the largest hot spot swell, multiple recent studies have confirmed the existence of low‐velocity upper mantle beneath the Hawaiian chain, with plausible connections to a deep plume source (Cheng et al, ; Laske et al, ; Wolfe et al, , ). The Sp receiver‐function study by Rychert et al () identifies a velocity interface at 100–150‐km depth that they identify with the onset of melting as the hot plume rises through the pressure‐dependent solidus.…”

Section: Paradigm Shootout: Plume Plutonism Versus Metasomatismmentioning

confidence: 96%

Why Is Crustal Underplating Beneath Many Hot Spot Islands Anisotropic?

Park

Rye

2019

Geochem Geophys Geosyst

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High‐frequency harmonic regression (2.0–4.0‐Hz cutoff) of receiver functions at two long‐running seismic observatories at mid‐Pacific hot spot islands confirms earlier detections of underplated material with seismic velocities intermediate to crust and mantle, and reveals it to be multilayered and anisotropic within ~30 km of the surface. Magmatic underplating beneath the oceanic Moho has been proposed to accompany basaltic melt that erupts at the seafloor and (eventually) atop a subaerial volcano. An alternate hypothesis is “metasomatic underplating” whereby crustal fractures developed during magma ascent allow seawater to infiltrate and to serpentinize the sub‐Moho mantle partially. Metasomatic underplating would lower seismic wave speeds, promote the buoyancy of the hot spot swell, and induce textural anisotropy as metamorphic expansion of olivine‐rich peridotite promotes a crack network along which serpentinization spreads. Differential expansion of mantle peridotite and crustal gabbro promotes cracks in the crust that offer new pathways for seawater to descend to the Moho, allowing metasomatic underplating to expand laterally and to contribute anisotropy to the underplated layer. Rare serpentinized mantle xenoliths confirm that crack textures can develop during serpentinization at depth. The discovery of iron‐oxidizing microbial mats on the seafloor flank of the Loihi volcano, and many locations of diffuse low‐temperature venting worldwide, is consistent with the circulation of metasomatic fluids with reducing chemistry, sourced from serpentinization at depth. Posteruptive uplift of Santa Maria Island (Azores), and asymmetry of the Hawaiian swell, suggests that underplating requires 2–4 Myr to complete, suggesting that fluid infiltration is slow, subject to cycles of blockage and fresh fracturing.

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Seismic Constraints on a Double‐Layered Asymmetric Whole‐Mantle Plume Beneath Hawai‘i

Cited by 21 publications

References 88 publications

Textural and Compositional Changes in the Lithospheric Mantle Atop the Hawaiian Plume: Consequences for Seismic Properties

Textural and Compositional Changes in the Lithospheric Mantle Atop the Hawaiian Plume: Consequences for Seismic Properties

Crustal structure across the eastern North American margin from ambient noise tomography

Why Is Crustal Underplating Beneath Many Hot Spot Islands Anisotropic?

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