Seismic anisotropy in the lowermost mantle near the Perm Anomaly

Long, Maureen D.; Lynner, Colton

doi:10.1002/2015gl065506

Cited by 37 publications

(36 citation statements)

References 37 publications

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“…Moreover, the prediction is consistent with deformation on the eastern boundary of the Perm Anomaly and the presence of high seismic velocity structures to the east of the Perm Anomaly that also reveal anisotropy in SKS–SKKS splitting measurements18. Together with seismic observations18 and previous models13141516, our results challenge the long-term fixity and rigidity of deep-mantle thermochemical structures.…”

Section: Resultssupporting

confidence: 88%

“…This ongoing westward flow is compatible with SKS–SKKS splitting measurements revealing anisotropy with a fast east–west direction in the lowermost mantle under eastern Europe and western Russia18, potentially due to lattice preferred-orientation of post-perovskite34. Moreover, the prediction is consistent with deformation on the eastern boundary of the Perm Anomaly and the presence of high seismic velocity structures to the east of the Perm Anomaly that also reveal anisotropy in SKS–SKKS splitting measurements18. Together with seismic observations18 and previous models13141516, our results challenge the long-term fixity and rigidity of deep-mantle thermochemical structures.…”

Section: Resultssupporting

confidence: 86%

“…The coherent translation of the discrete, Perm-like anomaly allows us to estimate an average motion rate of 1 cm year −1 over the last 150 Myr. This ongoing westward flow is compatible with SKS–SKKS splitting measurements revealing anisotropy with a fast east–west direction in the lowermost mantle under eastern Europe and western Russia18, potentially due to lattice preferred-orientation of post-perovskite34. Moreover, the prediction is consistent with deformation on the eastern boundary of the Perm Anomaly and the presence of high seismic velocity structures to the east of the Perm Anomaly that also reveal anisotropy in SKS–SKKS splitting measurements18.…”

Section: Resultssupporting

confidence: 83%

“…However, numerical models suggest that the influence of sinking slabs1112 should result in LLSVP deformation and motion13141516 over hundreds of million years. Additionally, measurements of differential splitting of SKS and SKKS seismic phases reveal anisotropy along the boundary of the African LLSVP17 and along the eastern boundary of the Perm Anomaly18, suggesting deformation is occurring on the edges of these structures. Finally, while SKS phases passing along the edge of LLSVPs suggest gradients in shear velocity that are too large to be explained by thermal variations alone1920, how chemically distinct LLSVPs are from the rest of the mantle remains unclear21.…”

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confidence: 99%

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Origin and evolution of the deep thermochemical structure beneath Eurasia

et al. 2017

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A unique structure in the Earth's lowermost mantle, the Perm Anomaly, was recently identified beneath Eurasia. It seismologically resembles the large low-shear velocity provinces (LLSVPs) under Africa and the Pacific, but is much smaller. This challenges the current understanding of the evolution of the plate–mantle system in which plumes rise from the edges of the two LLSVPs, spatially fixed in time. New models of mantle flow over the last 230 million years reproduce the present-day structure of the lower mantle, and show a Perm-like anomaly. The anomaly formed in isolation within a closed subduction network ∼22,000 km in circumference prior to 150 million years ago before migrating ∼1,500 km westward at an average rate of 1 cm year−1, indicating a greater mobility of deep mantle structures than previously recognized. We hypothesize that the mobile Perm Anomaly could be linked to the Emeishan volcanics, in contrast to the previously proposed Siberian Traps.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 86%

Section: Resultssupporting

confidence: 83%

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confidence: 99%

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Origin and evolution of the deep thermochemical structure beneath Eurasia

et al. 2017

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“…Karato and Li (1992) expected that diffusion creep should be the dominant deformation mechanism in lower mantle bridgmanite. This is also supported by the fact that seismic anisotropy, which would be expected if the alternative dislocation creep mechanism is dominant, is largely absent in the lower mantle, except at the base of the mantle near the edges of TUZO and the smaller Perm anomaly (Ford et al 2015;Long and Lynner 2015). Hence the numerical models are characterized by large-scale flow in the lower mantle: Sinking slabs and rising plumes supply the main driving forces, but are also part of large convection cells.…”

Section: Geodynamic Modelsmentioning

confidence: 48%

Earth evolution and dynamics—a tribute to Kevin Burke

et al. 2016

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Kevin Burke's original and thought-provoking contributions have been published steadily for the past sixty years, and more than a decade ago he set out to resolve how plate tectonics and mantle plumes interact by proposing a simple conceptual model, which we will refer to as "the Burkian Earth". On the Burkian Earth, mantle plumes take us from the deepest mantle to sub-lithospheric depths, where partial melting occurs, and to the surface, where hotspot lavas erupt today, and where large igneous provinces and kimberlites have erupted episodically in the past. The arrival of a plume head contributes to continental break-up and punctuates plate tectonics by creating and modifying plate boundaries. Conversely, plate tectonics makes an essential contribution to the mantle through subduction. Slabs restore mass to the lowermost mantle and are the triggering mechanism for plumes that rise from the margins of large-scale low shear-wave velocity structures in the lowermost mantle, that Kevin christened TUZO and JASON. Situated just above the core-mantle boundary beneath Africa and the Pacific, these are two stable and antipodal thermochemical piles, which Kevin reasons represent the immediate after-effect of the moon-forming event and the final magma ocean crystallization.

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Overriding plate, mantle wedge, slab, and subslab contributions to seismic anisotropy beneath the northern Central Andean Plateau

Long

Biryol

Eakin

et al. 2016

Geochem Geophys Geosyst

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The Central Andean Plateau, the second‐highest plateau on Earth, overlies the subduction of the Nazca Plate beneath the central portion of South America. The origin of the high topography remains poorly understood, and this puzzle is intimately tied to unanswered questions about processes in the upper mantle, including possible removal of the overriding plate lithosphere and interaction with the flow field that results from the driving forces associated with subduction. Observations of seismic anisotropy can provide important constraints on mantle flow geometry in subduction systems. The interpretation of seismic anisotropy measurements in subduction settings can be challenging, however, because different parts of the subduction system may contribute, including the overriding plate, the mantle wedge above the slab, the slab itself, and the deep upper mantle beneath the slab. Here we present measurements of shear wave splitting for core phases (SKS, SKKS, PKS, and sSKS), local S, and source‐side teleseismic S phases that sample the upper mantle beneath southern Peru and northern Bolivia, relying mostly on data from the CAUGHT experiment. We find evidence for seismic anisotropy within most portions of the subduction system, although the overriding plate itself likely makes only a small contribution to the observed delay times. Average fast orientations generally trend roughly trench‐parallel to trench‐oblique, contradicting predictions from the simplest two‐dimensional flow models and olivine fabric scenarios. Our measurements suggest complex, layered anisotropy beneath the northern portion of the Central Andean Plateau, with significant departures from a two‐dimensional mantle flow regime.

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Seismic anisotropy in the lowermost mantle near the Perm Anomaly

Cited by 37 publications

References 37 publications

Origin and evolution of the deep thermochemical structure beneath Eurasia

Origin and evolution of the deep thermochemical structure beneath Eurasia

Earth evolution and dynamics—a tribute to Kevin Burke

Overriding plate, mantle wedge, slab, and subslab contributions to seismic anisotropy beneath the northern Central Andean Plateau

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