High surface topography related to upper mantle flow beneath Eastern Anatolia

High-resolution seismic models of three-dimensional mantle heterogeneity are interpreted in terms of upper mantle thermal and compositional anomalies. These anomalies produce density perturbations that drive mantle flow and corresponding convection-related geophysical observables, such as the nonhydrostatic geoid, free-air gravity anomalies, and dynamic surface topography, and provide constraints on internal mantle density structure. The convection related observables are corrected for the isostatically compensated crustal heterogeneity and compared with those predicted by tomography-based mantle flow models. Occam inversions of the surface topography and gravity data provide inferences of the velocity–density scaling coefficients, which characterize mantle density anomalies below North America. The inferred density anomalies require simultaneous contributions from temperature and composition. The density and seismic shear velocity anomalies place constraints on the thermochemical structure of the mantle beneath the North American craton. Perturbations in the molar ratio of iron, R = XFe/(XFe + XMg), are used to quantify the compositional anomalies in terms of iron depletion in the sub-continental mantle. Estimates of the extent of basalt depletion in the tectosphere beneath North America are obtained. This depletion is interpreted to produce a local balance between positive chemical buoyancy and the negative thermal buoyancy that would otherwise be produced by the colder temperatures of the sub-cratonic mantle relative to its sub-oceanic counterpart.

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Feedbacks between a non-Newtonian upper mantle, mantle viscosity structure and mantle dynamics

Geophysical Journal International ◽

10.1093/gji/ggaa495 ◽

2020 ◽

Vol 224 (2) ◽

pp. 961-972

Author(s):

A G Semple ◽

A Lenardic

Keyword(s):

Upper Mantle ◽

Lower Mantle ◽

Mantle Convection ◽

Mantle Flow ◽

Mantle Dynamics ◽

Plate Motions ◽

Low Viscosity ◽

Mantle Viscosity ◽

Flow Feature ◽

Mantle Rheology

SUMMARY Previous studies have shown that a low viscosity upper mantle can impact the wavelength of mantle flow and the balance of plate driving to resisting forces. Those studies assumed that mantle viscosity is independent of mantle flow. We explore the potential that mantle flow is not only influenced by viscosity but can also feedback and alter mantle viscosity structure owing to a non-Newtonian upper-mantle rheology. Our results indicate that the average viscosity of the upper mantle, and viscosity variations within it, are affected by the depth to which a non-Newtonian rheology holds. Changes in the wavelength of mantle flow, that occur when upper-mantle viscosity drops below a critical value, alter flow velocities which, in turn, alter mantle viscosity. Those changes also affect flow profiles in the mantle and the degree to which mantle flow drives the motion of a plate analogue above it. Enhanced upper-mantle flow, due to an increasing degree of non-Newtonian behaviour, decreases the ratio of upper- to lower-mantle viscosity. Whole layer mantle convection is maintained but upper- and lower-mantle flow take on different dynamic forms: fast and concentrated upper-mantle flow; slow and diffuse lower-mantle flow. Collectively, mantle viscosity, mantle flow wavelengths, upper- to lower-mantle velocities and the degree to which the mantle can drive plate motions become connected to one another through coupled feedback loops. Under this view of mantle dynamics, depth-variable mantle viscosity is an emergent flow feature that both affects and is affected by the configuration of mantle and plate flow.

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A subduction influence on ocean ridge basalts outside the Pacific subduction shield

Nature Communications ◽

10.1038/s41467-021-25027-2 ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

A. Y. Yang ◽

C. H. Langmuir ◽

Y. Cai ◽

P. Michael ◽

S. L. Goldstein ◽

...

Keyword(s):

Upper Mantle ◽

The Arctic ◽

Mantle Flow ◽

Mantle Heterogeneity ◽

Gakkel Ridge ◽

The Pacific ◽

Mid Ocean Ridge ◽

The Pacific Ocean ◽

Back Arc ◽

Ocean Ridge

AbstractThe plate tectonic cycle produces chemically distinct mid-ocean ridge basalts and arc volcanics, with the latter enriched in elements such as Ba, Rb, Th, Sr and Pb and depleted in Nb owing to the water-rich flux from the subducted slab. Basalts from back-arc basins, with intermediate compositions, show that such a slab flux can be transported behind the volcanic front of the arc and incorporated into mantle flow. Hence it is puzzling why melts of subduction-modified mantle have rarely been recognized in mid-ocean ridge basalts. Here we report the first mid-ocean ridge basalt samples with distinct arc signatures, akin to back-arc basin basalts, from the Arctic Gakkel Ridge. A new high precision dataset for 576 Gakkel samples suggests a pervasive subduction influence in this region. This influence can also be identified in Atlantic and Indian mid-ocean ridge basalts but is nearly absent in Pacific mid-ocean ridge basalts. Such a hemispheric-scale upper mantle heterogeneity reflects subduction modification of the asthenospheric mantle which is incorporated into mantle flow, and whose geographical distribution is controlled dominantly by a “subduction shield” that has surrounded the Pacific Ocean for 180 Myr. Simple modeling suggests that a slab flux equivalent to ~13% of the output at arcs is incorporated into the convecting upper mantle.

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Observation of subnanometre-high surface topography with X-ray reflection phase-contrast microscopy

Nature Physics ◽

10.1038/nphys419 ◽

2006 ◽

Vol 2 (10) ◽

pp. 700-704 ◽

Cited By ~ 38

Author(s):

Paul Fenter ◽

Changyong Park ◽

Zhan Zhang ◽

Steve Wang

Keyword(s):

Surface Topography ◽

Phase Contrast ◽

High Surface ◽

Phase Contrast Microscopy ◽

X Ray ◽

Reflection Phase ◽

Contrast Microscopy

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The Upper Mantle Flow Beneath the North China Platform

Mechanics Problems in Geodynamics Part II ◽

10.1007/978-3-0348-9200-1_12 ◽

1996 ◽

pp. 649-659

Author(s):

Rong-Shan Fu ◽

Jian-Hua Huang ◽

Zhe-Xun Wei

Keyword(s):

Upper Mantle ◽

North China ◽

Mantle Flow ◽

North China Platform ◽

The North

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Antarctic Upper Mantle Rheology

Geological Society London Memoirs ◽

10.1144/m56-2020-19 ◽

2021 ◽

pp. M56-2020-19

Author(s):

E. R. Ivins ◽

W. van der Wal ◽

D. A. Wiens ◽

A. J. Lloyd ◽

L. Caron

Keyword(s):

Wave Velocity ◽

Upper Mantle ◽

Effective Viscosity ◽

Seismic Velocity ◽

Imaging Techniques ◽

Three Dimensional ◽

Velocity Model ◽

Mantle Flow ◽

S Wave ◽

Velocity Changes

AbstractThe Antarctic mantle and lithosphere are known to have large lateral contrasts in seismic velocity and tectonic history. These contrasts suggest differences in the response time scale of mantle flow across the continent, similar to those documented between the northeastern and southwestern upper mantle of North America. Glacial isostatic adjustment and geodynamical modeling rely on independent estimates of lateral variability in effective viscosity. Recent improvements in imaging techniques and the distribution of seismic stations now allow resolution of both lateral and vertical variability of seismic velocity, making detailed inferences about lateral viscosity variations possible. Geodetic and paleo sea-level investigations of Antarctica provide quantitative ways of independently assessing the three-dimensional mantle viscosity structure. While observational and causal connections between inferred lateral viscosity variability and seismic velocity changes are qualitatively reconciled, significant improvements in the quantitative relations between effective viscosity anomalies and those imaged by P- and S-wave tomography have remained elusive. Here we describe several methods for estimating effective viscosity from S-wave velocity. We then present and compare maps of the viscosity variability beneath Antarctica based on the recent S-wave velocity model ANT-20 using three different approaches.

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Supplemental Material: Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

10.1130/geol.s.12773969 ◽

2020 ◽

Author(s):

Vadim Levin ◽

et al.

Keyword(s):

Data Analysis ◽

Costa Rica ◽

Upper Mantle ◽

Seismic Anisotropy ◽

Data Sources ◽

Mantle Flow ◽

Analysis Methodology ◽

The Pacific ◽

Wave Splitting ◽

The Caribbean

Data sources, details of data analysis methodology, and additional diagrams and maps of shear wave splitting measurements.<br>

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Seismic anisotropy reveals crustal flow driven by mantle vertical loading in the Pacific NW

Science Advances ◽

10.1126/sciadv.abb0476 ◽

2020 ◽

Vol 6 (28) ◽

pp. eabb0476

Author(s):

Jorge C. Castellanos ◽

Jonathan Perry-Houts ◽

Robert W. Clayton ◽

YoungHee Kim ◽

A. Christian Stanciu ◽

...

Keyword(s):

Pacific Northwest ◽

Upper Mantle ◽

Seismic Anisotropy ◽

Azimuthal Anisotropy ◽

Mantle Flow ◽

Near Surface ◽

Vertical Loading ◽

The Pacific ◽

Anisotropy Model ◽

Lithosphere Dynamics

Buoyancy anomalies within Earth’s mantle create large convective currents that are thought to control the evolution of the lithosphere. While tectonic plate motions provide evidence for this relation, the mechanism by which mantle processes influence near-surface tectonics remains elusive. Here, we present an azimuthal anisotropy model for the Pacific Northwest crust that strongly correlates with high-velocity structures in the underlying mantle but shows no association with the regional mantle flow field. We suggest that the crustal anisotropy is decoupled from horizontal basal tractions and, instead, created by upper mantle vertical loading, which generates pressure gradients that drive channelized flow in the mid-lower crust. We then demonstrate the interplay between mantle heterogeneities and lithosphere dynamics by predicting the viscous crustal flow that is driven by local buoyancy sources within the upper mantle. Our findings reveal how mantle vertical load distribution can actively control crustal deformation on a scale of several hundred kilometers.

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Seismic anisotropy in southern Costa Rica confirms upper mantle flow from the Pacific to the Caribbean

Geology ◽

10.1130/g47826.1 ◽

2020 ◽

Vol 49 (1) ◽

pp. 8-12 ◽

Cited By ~ 1

Author(s):

Vadim Levin ◽

Stephen Elkington ◽

James Bourke ◽

Ivonne Arroyo ◽

Lepolt Linkimer

Keyword(s):

Costa Rica ◽

Upper Mantle ◽

Seismic Anisotropy ◽

Volcanic Eruptions ◽

Central American ◽

Mantle Flow ◽

Dynamic Topography ◽

The Pacific ◽

The Caribbean ◽

Surrounding Areas

Abstract Surrounded by subducting slabs and continental keels, the upper mantle of the Pacific is largely prevented from mixing with surrounding areas. One possible outlet is beneath the southern part of the Central American isthmus, where regional observations of seismic anisotropy, temporal changes in isotopic composition of volcanic eruptions, and considerations of dynamic topography all suggest upper mantle flow from the Pacific to the Caribbean. We derive new constraints on the nature of seismic anisotropy in the upper mantle of southern Costa Rica from observations of birefringence in teleseismic shear waves. Fast and slow components separate by ∼1 s, with faster waves polarized along the 40°–50° (northeast) direction, near-orthogonally to the Central American convergent margin. Our results are consistent with upper mantle flow from the Pacific to the Caribbean and require an opening in the lithosphere subducting under the region.

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