The effect of subducting slabs in global shear wave tomography

Lu, Chang; Grand, S. P.

doi:10.1093/gji/ggw072

Cited by 51 publications

(54 citation statements)

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“…Goes et al (2017) wrote "The classic example of a deeply penetrating plate is the Cocos plate, subducting along the eastern side of the Pacific, below Central America … ." Some subsequent tomograms, such as GypSum-S (Simmons et al, 2010) and TX2015 (Lu & Grand, 2016) (Figure 7), show similar continuous high-speed zones approaching the core-mantle boundary. Such continuity in others, like HMSL-S06 (Houser et al, 2008) and SEMUCB-WM1 (French & Romanowicz, 2014) (Figure 7), as well as Ren et al (2007) in their Figure 6, is less clear.…”

Section: The Boundary Between the Upper And Lower Mantle (And Layeredmentioning

confidence: 91%

“…Cross sections of S wave speed anomalies from 30.1°N, 117.1°W (left) to 30.2°N, 56.4°W (right), the profile shown by Grand et al () beneath the southern United States and western Atlantic (see Figure ): HMSL‐S06 (Houser et al, ), GyPSuM‐S (Simmons et al, ), S40RTS (Ritsema et al, ), SEMUCB‐WM1 (French & Romanowicz, ), TX2015 (Lu & Grand, ), and SEISMGLOB2 (Durand et al, ). Dashed lines show depths of 410, 660, and 1,000 km.…”

Section: The Boundary Between the Upper And Lower Mantle (And Layeredmentioning

confidence: 93%

“…This paper contains no new data, but to make Figures and , I have replotted published data using https://www.earth.ox.ac.uk/~smachine/cgi/index.php of Hosseini et al (). Those data were taken from Durand et al (), French and Romanowicz (), Houser et al (), Li et al (), Lu and Grand (), Obayashi et al (), Ritsema et al (), Simmons et al (, ), and Tesoniero et al ().…”

Section: Acknowledgmentsmentioning

confidence: 99%

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Lower Mantle Dynamics Perceived With 50 Years of Hindsight From Plate Tectonics

Molnár

2019

Geochem Geophys Geosyst

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Continually improving resolution of lower mantle structure and understanding of mantle dynamics suggest that, as in the plate-tectonics era, the upper and lower mantle may undergo little exchange. Although the phase transition at~660 km forms the sharpest seismologically mapped boundary within the mantle, another at 1,000 (±100) km might be more important for geodynamics. Contrasts in density and viscosity may limit penetration of upper and lower mantle through this boundary. Strong evidence, if still not definitive, calls for chemical heterogeneity of the lower mantle that manifests itself in a few energetic plumes rising from near the core mantle boundary and slowly evolving, larger piles or blobs of chemically distinct material. Those blobs or piles may deform little on billion-year timescales. Convection in the lower mantle might dictate some aspects of flow in the upper mantle, such as the positions of plumes and hot spots and the breakup of supercontinents, but its contribution to the speeds and directions that plates move might be negligible. The improved understanding of mantle convection has not overturned the simple, 50-year-old image that plates "drive themselves," with forces per unit length pushing them apart at spreading centers, excess mass in downgoing slabs pulling them down, and viscous drag on their bases (and tops at subduction zones) retarding movement. Remaining challenges include determining how convection in the lower mantle affects geologic history and using that history to constrain lower mantle dynamics.Plain Language Summary Fifty years ago, plate tectonics united many aspects of the surface geology of the Earth, but little connection to the lower mantle was seen. Today, most view plate tectonics as the relative movements of cold, top, stiff boundary layers of a convecting system that reaches to the core-mantle boundary and with aspects of the deep structure not foreseen decades ago. Large provinces in the deepest~1,000 km, in which P and S wave speeds are relatively low, not only seem to be chemically different from the neighboring mantle and from that at shallower depths, but their distribution also correlates with some aspects of the overlying surface geology, including the positions of major plumes rising from deep in the mantle and the positions of continents 100 to 200 Ma. These correlations imply a geodynamic connection between the lower mantle and the crust. Scaling laws derived from experiments in geophysical fluid mechanics suggest that the chemically distinct provinces may be relics from the earliest formation of the earth, but if not, they nevertheless have evolved slowly on the timescales of geologic eras. A concurrent emerging view of the lower mantle, however, also places increased emphasis on a boundary at~1,000 (±100) km depth, and this boundary might define a barrier to cold sinking slabs of lithosphere. A few isolated plumes of hot material that are also chemically different from most of the mantle penetrate this interface at 1,000 km, but it seems possible that this...

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Section: The Boundary Between the Upper And Lower Mantle (And Layeredmentioning

confidence: 91%

Section: The Boundary Between the Upper And Lower Mantle (And Layeredmentioning

confidence: 93%

Section: Acknowledgmentsmentioning

confidence: 99%

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Lower Mantle Dynamics Perceived With 50 Years of Hindsight From Plate Tectonics

Molnár

2019

Geochem Geophys Geosyst

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“…Thus, relatively steep ray paths (such as SKS) can be used to define local boundary sharpness and small features such as ULVZs using the SPdKS arrival. Defining the boundaries of the mid-Pacific LLSVP has been difficult using seismic tomographic methods (Text S2), especially considering uncertainty in event locations caused by slab structure (Lu & Grand, 2016;Zhan et al, 2014). In contrast, the LLVSP beneath the mid-Pacific is more difficult to define because of the few seismic stations available regionally.…”

Section: Introductionmentioning

confidence: 99%

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Sun

Helmberger

Lai

et al. 2019

Geophysical Research Letters

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At the core‐mantle boundary, most observed ultralow velocity zones (ULVZs) cluster along the edges of the large low shear velocity provinces (LLSVPs) and provide key information on the composition, dynamics, and evolution of the lower mantle. However, their detailed structure near slab‐like structures beneath the mid‐Pacific remains particularly challenging because of the lack of station coverage. While most studies of ULVZs concentrate on SKS‐complexity, here we report on the multipathing of ScS, which expands the sampling for ULVZs. We find the strongest multipathing along a ULVZ patch located just south of Hawaii and the far northeastern edge of the LLSVP, in a zone ~200 km in width and extending 600 km southward. The anomalous ScS travel times and distorted Sdiff waveforms further reveal patches interrupted by observed enhanced D″ indicative of slab‐debris influence on the complexity of the northeastern boundary of the mid‐Pacific LLSVP.

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“…(left) Relevant features in the western United States. Color‐coded track shows the position of the plume conduit versus depth inferred from the tomography model of Nelson and Grand (), using TX2016 (Lu & Grand, ) as the starting model. Tickmarks are every 500 km in depth.…”

Section: Introduction: Yellowstone—a Whole‐mantle Plume?mentioning

confidence: 99%

Yellowstone Plume Conduit Tilt Caused by Large‐Scale Mantle Flow

Steinberger

Nelson

Grand

et al. 2019

Geochem Geophys Geosyst

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Mantle plumes are hot upwellings of rock thought to originate at the core-mantle boundary.As they rise through the mantle, their conduits may become tilted due to lateral large-scale mantle flow. Recent tomographic images have revealed a strongly tilted plume conduit starting at the core-mantle boundary beneath northern Baja California rising toward the Yellowstone hot spot from the southwest. Here we perform numerical computations of plumes deflected in large-scale mantle flow with the aim of finding if realistic model parameter ranges exist that yield a good fit with the tomographically observed conduit. We restrict ourselves to models that yield reasonable results for plume conduit tilt and hot spot motion globally. These models require high viscosity ≈10 23 Pa s at some lower mantle depths. For a plume head reaching the surface 17 Ma, corresponding to the start of the Columbia River Basalts, our models require rise times ≈80 Myr or longer to match the tilt of the conduit observed by tomography. We used several tomography models to determine mantle density with almost all models predicting southwestward flow in the lowermost mantle beneath the western United States. Exact details of the shape of the predicted conduit's southwesterly tilt vary, depending on the density and viscosity structures we used. In many cases we find comparatively strong tilts in two depth ranges, in the upper and lower portions of the mantle, which is also a characteristic of the tomographically observed conduit. We expect that future models may help to constrain large-scale flow by matching these corresponding depth ranges.

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The effect of subducting slabs in global shear wave tomography

Cited by 51 publications

References 51 publications

Lower Mantle Dynamics Perceived With 50 Years of Hindsight From Plate Tectonics

Lower Mantle Dynamics Perceived With 50 Years of Hindsight From Plate Tectonics

Slab Control on the Northeastern Edge of the Mid‐Pacific LLSVP Near Hawaii

Yellowstone Plume Conduit Tilt Caused by Large‐Scale Mantle Flow

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