Paired EMI-HIMU hotspots in the South Atlantic—Starting plume heads trigger compositionally distinct secondary plumes?

Age-progressive volcanism is generally accepted as the surface expression of deep-rooted mantle plumes, which are enigmatically linked with the African and Pacific large low–shear velocity provinces (LLSVPs). We present geochemical and geochronological data collected from the oldest portions of the age-progressive enriched mantle one (EMI)-type Tristan-Gough track. They are part of a 30- to 40-million year younger age-progressive hotspot track with St. Helena HIMU (high time-integrated 238U/204Pb) composition, which is also observed at the EMI-type Shona hotspot track in the southernmost Atlantic. Whereas the primary EMI-type hotspots overlie the margin of the African LLSVP, the HIMU-type hotspots are located above a central portion of the African LLSVP, reflecting a large-scale geochemical zonation. We propose that extraction of large volumes of EMI-type mantle from the margin of the LLSVP by primary plume heads triggered upwelling of HIMU material from a more internal domain of the LLSVP, forming secondary plumes.

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The relationships between large-scale variations in shear velocity, density, and compressional velocity in the Earth's mantle

Journal of Geophysical Research Solid Earth ◽

10.1002/2015jb012679 ◽

2016 ◽

Vol 121 (4) ◽

pp. 2737-2771 ◽

Cited By ~ 43

Author(s):

P. Moulik ◽

G. Ekström

Keyword(s):

Large Scale ◽

Shear Velocity ◽

Earth’S Mantle ◽

Compressional Velocity

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SPAN512: A new mid-latitude pulsar survey with the Nançay Radio Telescope

Proceedings of the International Astronomical Union ◽

10.1017/s1743921312024179 ◽

2012 ◽

Vol 8 (S291) ◽

pp. 375-377 ◽

Cited By ~ 1

Author(s):

Gregory Desvignes ◽

Ismaël Cognard ◽

David Champion ◽

Patrick Lazarus ◽

Patrice Lespagnol ◽

...

Keyword(s):

Radio Telescope ◽

Large Scale ◽

High Time ◽

Frequency Resolution ◽

Integration Time ◽

Sensitivity Limit ◽

Long Period ◽

Large Bandwidth ◽

L Band ◽

Better Than

AbstractWe present an ongoing survey with the Nançay Radio Telescope at L-band. The targeted area is 74° ≲ l < 150° and 3.5° < |b| < 5°. This survey is characterized by a long integration time (18 min), large bandwidth (512 MHz) and high time and frequency resolution (64 μs and 0.5 MHz) giving a nominal sensitivity limit of 0.055 mJy for long period pulsars. This is about 2 times better than the mid-latitude HTRU survey, and is designed to be complementary with current large scale surveys. This survey will be more sensitive to transients (RRATs, intermittent pulsars), distant and faint millisecond pulsars as well as scintillating sources (or any other kind of radio faint sources) than all previous short-integration surveys.

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Effective buoyancy ratio: a new parameter to characterize thermo-chemical mixing in the Earth's mantle

Solid Earth Discussions ◽

10.5194/sed-6-2675-2014 ◽

2014 ◽

Vol 6 (2) ◽

pp. 2675-2697

Author(s):

A. Galsa ◽

M. Herein ◽

L. Lenkey ◽

M. P. Farkas ◽

G. Taller

Keyword(s):

Mixing Time ◽

Initial Density ◽

Shear Velocity ◽

Dense Layer ◽

Earth’S Mantle ◽

A Value ◽

Short Time ◽

Chemical Mixing ◽

Buoyancy Ratio ◽

Low Shear

Abstract. Numerical modeling has been carried out in a 2-D cylindrical shell domain to quantify the evolution of a primordial dense layer around the core mantle boundary. Effective buoyancy ratio, Beff was introduced to characterize the evolution of the two-layer thermo-chemical convection in the Earth's mantle. Beff decreases with time due to (1) warming the compositionally dense layer, (2) cooling the overlying mantle, (3) eroding the dense layer by thermal convection in the overlying mantle, and (4) diluting the dense layer by inner convection. When Beff reaches the instability point, Beff = 1, effective thermo-chemical convection starts, and the mantle will be mixed (Beff = 0) during a short time. A parabolic relation was revealed between the initial density difference of the layers and the mixing time. Morphology of large low shear velocity provinces as well as results from seismic tomography and normal mode data suggest a value of Beff ≥ 1 for the mantle.

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Predictors of High Costs of Care among Otolaryngology Patients

Otolaryngology ◽

10.1177/0194599819838843 ◽

2019 ◽

Vol 161 (2) ◽

pp. 271-277 ◽

Cited By ~ 1

Author(s):

Karthik Balakrishnan ◽

James P. Moriarty ◽

Jordan Rosedahl ◽

Colin L. Driscoll ◽

Bijan J. Borah

Keyword(s):

Head And Neck ◽

Race And Ethnicity ◽

Large Scale ◽

Reference Group ◽

Cross Sectional ◽

Reconstructive Procedures ◽

Younger Age ◽

Adult Inpatient ◽

Pediatric Inpatient ◽

Adult Outpatient

Objectives Identify predictors of high-cost otolaryngology care. Study Design Cross-sectional. Setting Tertiary academic multispecialty hospital. Subjects/Methods All patients undergoing ≥1 otolaryngologic procedures from 2011 to 2015. Encounter costs were standardized using previously described methods approximating Medicare reimbursement. Patients were stratified by adult/pediatric and inpatient/outpatient. “Outliers” were defined as total encounter costs ≥95th percentile. Logistic regression measured predictors of outlier status. Results In total, 2433 adult inpatient encounters (95th percentile $57,611), 10,031 adult outpatient encounters ($10,772), 346 pediatric inpatient encounters ($84,639), and 3027 pediatric outpatient encounters ($8978) were included. For adult inpatient and outpatient, isolated head and neck oncologic procedures were the reference group. Among adult inpatients, laryngology and facial plastics procedures predicted higher odds of outlier status (odds ratio [OR] = 4.1 and 7.2). Involvement of multiple otolaryngology subspecialties increased the odds (OR = 4.7). Neck dissection and reconstructive procedures were the most common primary operations for adult inpatient outliers. For adult outpatients, several subspecialties had lower odds than head and neck (OR ≤0.44). Increased comorbidities predicted outliers for adult inpatient care (OR = 1.5); sex, age, race, and ethnicity did not. Cochlear implant was the most common primary operation among adult and pediatric outpatient outliers. Greater subspecialty involvement and increasing age predicted pediatric outpatient outliers (OR = 8.0 and 1.1); younger age and female sex predicted pediatric inpatient outliers (OR = 0.8 and 3.5). Airway procedures dominated pediatric inpatient outliers. Conclusion This is the first large-scale study of high-cost otolaryngology care across multiple subspecialties. Specific procedures and subspecialties and increased comorbidities predicted high-cost care. Contrary to previous studies, patient sex, race, and ethnicity did not.

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Competing Deformation Mechanisms in Periclase: Implications for Lower Mantle Anisotropy

Minerals ◽

10.3390/min9110650 ◽

2019 ◽

Vol 9 (11) ◽

pp. 650 ◽

Cited By ~ 2

Author(s):

Feng Lin ◽

Samantha Couper ◽

Mike Jugle ◽

Lowell Miyagi

Keyword(s):

Lower Mantle ◽

Seismic Anisotropy ◽

Shear Velocity ◽

Deformation Mechanisms ◽

Effect Of Temperature ◽

Lattice Strains ◽

Slip Activity ◽

Consistent Method ◽

Mantle Anisotropy ◽

Low Shear

Seismic anisotropy is observed above the core-mantle boundary in regions of slab subduction and near the margins of Large Low Shear Velocity Provinces (LLSVPs). Ferropericlase is believed to be the second most abundant phase in the lower mantle. As it is rheologically weak, it may be a dominant source for anisotropy in the lowermost mantle. Understanding deformation mechanisms in ferropericlase over a range of pressure and temperature conditions is crucial to interpret seismic anisotropy. The effect of temperature on deformation mechanisms of ferropericlase has been established, but the effects of pressure are still controversial. With the aim to clarify and quantify the effect of pressure on deformation mechanisms, we perform room temperature compression experiments on polycrystalline periclase to 50 GPa. Lattice strains and texture development are modeled using the Elasto-ViscoPlastic Self Consistent method (EVPSC). Based on modeling results, we find that { 110 } ⟨ 1 1 ¯ 0 ⟩ slip is increasingly activated with higher pressure and is fully activated at ~50 GPa. Pressure and temperature have a competing effect on activities of dominant slip systems. An increasing { 100 } ⟨ 011 ⟩ : { 110 } ⟨ 1 1 ¯ 0 ⟩ ratio of slip activity is expected as material moves from cold subduction regions towards hot upwelling region adjacent to LLSVPs. This could explain observed seismic anisotropy in the circum-Pacific region that appears to weaken near margins of LLVSPs.

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Velocity and density characteristics of subducted oceanic crust and the origin of lower-mantle heterogeneities

Nature Communications ◽

10.1038/s41467-019-13720-2 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 2

Author(s):

Wenzhong Wang ◽

Yinhan Xu ◽

Daoyuan Sun ◽

Sidao Ni ◽

Renata Wentzcovitch ◽

...

Keyword(s):

Phase Transition ◽

Oceanic Crust ◽

Seismic Tomography ◽

Lower Mantle ◽

Shear Velocity ◽

Calcium Ferrite ◽

Velocity Anomaly ◽

Mantle Heterogeneities ◽

Subducted Oceanic Crust ◽

Low Shear

AbstractSeismic heterogeneities detected in the lower mantle were proposed to be related to subducted oceanic crust. However, the velocity and density of subducted oceanic crust at lower-mantle conditions remain unknown. Here, we report ab initio results for the elastic properties of calcium ferrite‐type phases and determine the velocities and density of oceanic crust along different mantle geotherms. We find that the subducted oceanic crust shows a large negative shear velocity anomaly at the phase boundary between stishovite and CaCl2-type silica, which is highly consistent with the feature of mid-mantle scatterers. After this phase transition in silica, subducted oceanic crust will be visible as high-velocity heterogeneities as imaged by seismic tomography. This study suggests that the presence of subducted oceanic crust could provide good explanations for some lower-mantle seismic heterogeneities with different length scales except large low shear velocity provinces (LLSVPs).

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Detection of ridge-like structures in the Pacific Large Low-Shear-Velocity Province

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2011.12.024 ◽

2012 ◽

Vol 319-320 ◽

pp. 55-64 ◽

Cited By ~ 11

Author(s):

Nozomu Takeuchi

Keyword(s):

Shear Velocity ◽

The Pacific ◽

Low Shear

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The Simulation of Aggregated Colloids Under Flow

MRS Proceedings ◽

10.1557/proc-289-33 ◽

1992 ◽

Vol 289 ◽

Author(s):

John R. Melrose

Keyword(s):

Shear Rate ◽

Large Scale ◽

Shear Thinning ◽

High Shear ◽

Shear Rates ◽

Rouse Model ◽

High Shear Rates ◽

Structural Breakdown ◽

Large Scale Simulations ◽

Low Shear

AbstractAn overview is given of theories of aggregates under flow. These generally assume some sort of structural breakdown as the shear rate is increased. Models vary with both the rigidity of the bonding and the level of treatment of hydrodynamics. Results are presented for simulations of a Rouse model of non-rigid, (i.e. central force) weakly bonded aggregates. In large scale simulations different structures are observed at low and high shear rates. The change from one structure to another is associated with a change in the rate of shear thinning. The model captures low shear rate features of real systems absent in previous models: this feature is ascribed to agglomerate deformations. Quantitatively, the model is two orders of magnitude out from experiment but some scaling is possible.

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Coupled supercontinent–mantle plume events evidenced by oceanic plume record

Geology ◽

10.1130/g46754.1 ◽

2019 ◽

Vol 48 (2) ◽

pp. 159-163 ◽

Cited By ~ 3

Author(s):

Luc S. Doucet ◽

Zheng-Xiang Li ◽

Richard E. Ernst ◽

Uwe Kirscher ◽

Hamed Gamal El Dien ◽

...

Keyword(s):

Mantle Plume ◽

Shear Velocity ◽

Temporal Variations ◽

Large Igneous Provinces ◽

First Order ◽

The Past ◽

Igneous Provinces ◽

Island Basalt ◽

Supercontinent Cycle ◽

Low Shear

Abstract The most dominant features in the present-day lower mantle are the two antipodal African and Pacific large low-shear-velocity provinces (LLSVPs). How and when these two structures formed, and whether they are fixed and long lived through Earth history or dynamic and linked to the supercontinent cycles, remain first-order geodynamic questions. Hotspots and large igneous provinces (LIPs) are mostly generated above LLSVPs, and it is widely accepted that the African LLSVP existed by at least ca. 200 Ma beneath the supercontinent Pangea. Whereas the continental LIP record has been used to decipher the spatial and temporal variations of plume activity under the continents, plume records of the oceanic realm before ca. 170 Ma are mostly missing due to oceanic subduction. Here, we present the first compilation of an Oceanic Large Igneous Provinces database (O-LIPdb), which represents the preserved oceanic LIP and oceanic island basalt occurrences preserved in ophiolites. Using this database, we are able to reconstruct and compare the record of mantle plume activity in both the continental and oceanic realms for the past 2 b.y., spanning three supercontinent cycles. Time-series analysis reveals hints of similar cyclicity of the plume activity in the continent and oceanic realms, both exhibiting a periodicity of ∼500 m.y. that is comparable to the supercontinent cycle, albeit with a slight phase delay. Our results argue for dynamic LLSVPs where the supercontinent cycle and global subduction geometry control the formation and locations of the plumes.

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