Converted phases from sharp 1000 km depth mid-mantle heterogeneity beneath Western Europe

Jenkins, Jennifer; Deuss, Arwen; Cottaar, Sanne

doi:10.1016/j.epsl.2016.11.031

Cited by 55 publications

(63 citation statements)

References 48 publications

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“…Sporadic and weak conversions are present between about 850‐km and 1,000‐km depth. Seismic layering in the lower mantle have been observed previously (e.g., Jenkins et al, ; Waszek et al, ), but there are no known mineral phase transitions that could account for these observations.…”

Section: Receiver Functionsmentioning

confidence: 89%

Evidence of Subduction‐Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions

Maguire

Ritsema

Goes

2018

Geophysical Research Letters

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The subduction of the Farallon Plate has altered the temperature and composition of the mantle transition zone (MTZ) beneath the United States. We investigate MTZ structure by mapping P‐to‐S conversions at mineralogical phase changes using USArray waveform data and theoretical seismic profiles based on experimental constraints of phase transition properties as a function of temperature and composition. The width of the MTZ varies by about 35 km over the study region, corresponding to a temperature variation of more than 300 K. The MTZ is coldest and thickest beneath the eastern United States where high shear velocity anomalies are tomographically resolved. We detect intermittent P‐to‐S conversions at depths of 520 km and 730 km. The conversions at 730‐km depth are coherent beneath the southeastern United States and are consistent with basalt enrichment of about 50%, possibly due to the emplacement of a fragment of an oceanic plateau (i.e., the Hess conjugate).

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Section: Receiver Functionsmentioning

confidence: 89%

Evidence of Subduction‐Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions

Maguire

Ritsema

Goes

2018

Geophysical Research Letters

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“…Regarding a possible deeply held prejudice that has slowed understanding, the old‐timers—Francis Birch, Keith Bullen, Norman Haskell, and surely others—might have put the boundary between the upper and lower mantle in the right place, near 1,000 km, and not at 660 km as most have accepted, after that depth seemed to fit with simple images of plate tectonics. Recently, many have suggested that a boundary at 1,000 km is the more important for geodynamics (e.g., Ballmer et al, , ; Čížková & Bina, ; Durand et al, ; Fukao et al, , ; Jenkins et al, ; Marquardt & Miyagi, ; Morra et al, ; Rudolph et al, ; Vinnik et al, ; Wen & Anderson, , ). I argue that a boundary at 1,000 km not only fits seismological data well but also allows greater isolation between the upper and lower mantle than has, until recently, been widely assumed but not total isolation.…”

Section: Introductionmentioning

confidence: 99%

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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“…Even though the bulk lower mantle (LM) is considered well mixed above the D ′′ layer, heterogeneities in Earth's LM have also been disclosed by studies of geochemistry and seismology (Jenkins et al, ; Romanowicz & Wenk, ). These heterogeneities include isotopically and chemically distinct components from basaltic volcanism (Hofmann, ), heavier‐than‐average materials down to the core–mantle boundary (Trampert et al, ), and a decrease in shear wave velocity by more than 1.5–2% beneath hot spot volcanoes (French & Romanowicz, ).…”

Section: Introductionmentioning

confidence: 99%

Thermoelastic Properties of Aluminous Phases in MORB From First‐Principle Calculation: Implications for Earth's Lower Mantle

et al. 2018

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The mantle dynamics and mineralogy of the deep Earth are fundamentally influenced by the intrusion of subducted mid‐ocean ridge basalt (MORB). Calcium ferrite (CF) structure and calcium titanate (CT) structure phases are probable candidates for the end members of the complex aluminous solid solution in MORB under Earth's lower mantle (LM) conditions. In this paper, we investigate the thermoelastic properties of CF‐type MgAl2O4 (Mg‐CF), CT‐type MgAl2O4 (Mg‐CT), and CF‐type NaMg2Al5SiO12 (NaMg‐CF) under 32 to 142 GPa at 0, 2,000, and 3,000 K by ab initio molecular dynamics calculations. Using the thermal equations of state of the aluminous phases and considering the effects of composition and phase transition, we confirm that MORB is 0.7–1.8% denser than the surrounding mantle and support that oceanic plate could subduct at least to the bottom 200–300 km of the LM. At LM pressure‐temperature conditions, MORB has 0.3% faster VP, 2.2% slower Vs, and 1.9% faster VΦ than does the preliminary reference Earth model. Temperature dependencies of elasticity of Mg‐CF, Mg‐CT, and NaMg‐CF are calculated under LM conditions. We find that the temperature effect on different elastic constant components is complicated and the trend in the changes of derivatives of wave velocities with respect to temperature is contrary to other system (e.g., bridgmanite), so it is worth obtaining the elastic properties of mantle minerals under their relevant conditions. In addition, the significant elastic anisotropy due to the phase transition from CF structure to CT structure may lead to detectable seismic anisotropy at the bottom of the LM.

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Converted phases from sharp 1000 km depth mid-mantle heterogeneity beneath Western Europe

Cited by 55 publications

References 48 publications

Evidence of Subduction‐Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions

Evidence of Subduction‐Related Thermal and Compositional Heterogeneity Below the United States From Transition Zone Receiver Functions

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

Thermoelastic Properties of Aluminous Phases in MORB From First‐Principle Calculation: Implications for Earth's Lower Mantle

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