Seismic-geodynamic constraints on mantle flow: Implications for layered convection, mantle viscosity, and seismic anisotropy in the deep mantle.

2000 ◽  
pp. 3-36 ◽  
Author(s):  
Alessandro M. Forte
Keyword(s):  
Seismic Anisotropy ◽  
Mantle Flow ◽  
Mantle Viscosity ◽  
Deep Mantle

An investigation of seismic anisotropy in the lowermost mantle beneath Iceland

2019 ◽  
Vol 219 (Supplement_1) ◽  
pp. S152-S166 ◽  
Author(s):  
Jonathan Wolf ◽  
Neala Creasy ◽  
Angelo Pisconti ◽  
Maureen D Long ◽  
Christine Thomas
Keyword(s):  
Seismic Anisotropy ◽  
Horizontal Flow ◽  
Mantle Flow ◽  
Small Data ◽  
Vertical Flow ◽  
Low Velocity ◽  
Data Set ◽  
Study Region ◽  
Deep Mantle ◽  
Lowermost Mantle

SUMMARY Iceland represents one of the most well-known examples of hotspot volcanism, but the details of how surface volcanism connects to geodynamic processes in the deep mantle remain poorly understood. Recent work has identified evidence for an ultra-low velocity zone in the lowermost mantle beneath Iceland and argued for a cylindrically symmetric upwelling at the base of a deep mantle plume. This scenario makes a specific prediction about flow and deformation in the lowermost mantle, which can potentially be tested with observations of seismic anisotropy. Here we present an investigation of seismic anisotropy in the lowermost mantle beneath Iceland, using differential shear wave splitting measurements of S–ScS and SKS–SKKS phases. We apply our techniques to waves propagating at multiple azimuths, with the goal of gaining good geographical and azimuthal coverage of the region. Practical limitations imposed by the suboptimal distribution of global seismicity at the relevant distance ranges resulted in a relatively small data set, particularly for S–ScS. Despite this, however, our measurements of ScS splitting due to lowermost mantle anisotropy clearly show a rotation of the fast splitting direction from nearly horizontal for two sets of paths that sample away from the low velocity region (implying VSH > VSV) to nearly vertical for a set of paths that sample directly beneath Iceland (implying VSV > VSH). We also find evidence for sporadic SKS–SKKS discrepancies beneath our study region; while the geographic distribution of discrepant pairs is scattered, those pairs that sample closest to the base of the Iceland plume tend to be discrepant. Our measurements do not uniquely constrain the pattern of mantle flow. However, we carried out simple ray-theoretical forward modelling for a suite of plausible anisotropy mechanisms, including those based on single-crystal elastic tensors, those obtained via effective medium modelling for partial melt scenarios, and those derived from global or regional models of flow and texture development in the deep mantle. These simplified models do not take into account details such as possible transitions in anisotropy mechanism or deformation regime, and test a simplified flow field (vertical flow beneath the plume and horizontal flow outside it) rather than more detailed flow scenarios. Nevertheless, our modelling results demonstrate that our ScS splitting observations are generally consistent with a flow scenario that invokes nearly vertical flow directly beneath the Iceland hotspot, with horizontal flow just outside this region.

Subducting slab morphology and mantle transition zone upwelling in double-slab subduction models with inward-dipping directions

2019 ◽  
Vol 218 (3) ◽  
pp. 2089-2105 ◽  
Author(s):  
Tianyang Lyu ◽  
Zhiyuan Zhu ◽  
Benjun Wu
Keyword(s):  
Transition Zone ◽  
Lower Mantle ◽  
Numerical Models ◽  
Local Maximum ◽  
Substantial Effect ◽  
Mantle Flow ◽  
Slab Geometry ◽  
Mantle Transition Zone ◽  
Mantle Viscosity ◽  
Deep Mantle

SUMMARY Lithospheric plates on the Earth's surface interact with each other, producing distinctive structures comprising two descending slabs. Double-slab subduction with inward-dipping directions represents an important multiplate system that is not yet well understood. This paper presents 2-D numerical models that investigate the dynamic process of double-slab subduction with inward dipping, focussing on slab geometry and mantle transition zone upwelling flow. This unique double-slab configuration limits trench motion and causes steep downward slab movement, thus forming fold piles in the lower mantle and driving upward mantle flow between the slabs. The model results show the effects of lithospheric plate properties and lower-mantle viscosity on subducting plate kinematics, overriding plate stress and upward mantle flow beneath the overriding plate. Appropriate lower-mantle strength (such as an upper–lower mantle viscosity increase with a factor of 200) allows slabs to penetrate into the lower mantle with periodical buckling. While varying the length and thickness of a long overriding plate (≥2500) does not have a substantial effect on slab geometry, its viscosity has a marked impact on slab evolution and mantle flow pattern. When the overriding plate is strong, slabs exhibit an overturned geometry and hesitate to fold. Mantle transition zone upwelling velocity depends on the speed of descending slabs. The downward velocity of slabs with a large negative buoyancy (caused by thickness or density) is very fast, inducing a significant transition zone upwelling flow. A stiff slab slowly descends into the deep mantle, causing a small upward flow in the transition zone. In addition, the temporal variation of mantle upwelling velocity shows strong correlation with the evolution of slab folding geometry. In the double subduction system with inward-dipping directions, the mantle transition zone upwelling exhibits oscillatory rise with time. During the backward-folding stage, upwelling velocity reaches its local maximum. Our results provide new insights into the deep mantle source of intraplate volcanism in a three-plate interaction system such as the Southeast Asia region.

THE ROLE OF DEEP MANTLE FLOW IN SHAPING THE HAWAIIAN-EMPEROR BEND

2017 ◽  
Author(s):  
Simon Williams ◽  
◽  
Rakib Hassan ◽  
Dietmar Müller ◽  
Michael Gurnis ◽  
...  
Keyword(s):  
Mantle Flow ◽  
Deep Mantle

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

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.

Seismic anisotropy and mantle flow constrained by shear wave splitting in central Myanmar

2021 ◽  
Author(s):  
Enbo Fan ◽  
Yumei He ◽  
Yinshuang Ai ◽  
Stephen S. Gao ◽  
Kelly H. Liu ◽  
...  
Keyword(s):  
Shear Wave ◽  
Seismic Anisotropy ◽  
Shear Wave Splitting ◽  
Mantle Flow ◽  
Wave Splitting

Similarities between the Madeira and Canary Hotspots Revealed by Seismic Anisotropy from Teleseismic and Local Shear-Wave Splitting with the SIGHT Project

2021 ◽  
Author(s):  
David Schlaphorst ◽  
Graça Silveira ◽  
João Mata ◽  
Frank Krüger ◽  
Torsten Dahm ◽  
...  
Keyword(s):  
Shear Wave ◽  
Canary Islands ◽  
Delay Time ◽  
Seismic Anisotropy ◽  
Vertical Component ◽  
Mantle Flow ◽  
Crust And Upper Mantle ◽  
Length Scales ◽  
Flow Models ◽  
Using Data

<p>The Madeira and Canary archipelagos, located in the eastern North Atlantic, are two of many examples of hotspot surface expressions, but a better understanding of the crust and upper mantle structure beneath these regions is needed to investigate their structure in more detail. With the study of seismic anisotropy, it is possible to assess the rheology and structure of asthenosphere and lithosphere that can reflect a combination of mantle and crustal contributions.</p><p>Here, as part of the SIGHT project (SeIsmic and Geochemical constraints on the Madeira HoTspot), we present the first detailed study of seismic anisotropy beneath both archipelagos, using data collected from over 60 local three-component seismic land stations. Basing our observations on both teleseismic SKS and local S splitting, we are able to distinguish between multiple layers of anisotropy. We observe significant changes in delay time and fast shear-wave orientation patterns on short length-scales on the order of tens of kilometres beneath the western Canary Islands and Madeira Island. In contrast, the eastern Canary Islands and Porto Santo the pattern is much more uniform. The detected delay time increase and more complex orientation patterns beneath the western Canary Islands and Madeira can be attributed to mantle flow disturbed and diverted on small-length scales by a strong vertical component. This is a clear indication of the existence of a plume at each of those archipelagos, nowadays exerting a strong influence on the western and younger islands. We therefore conclude that a plume-like feature beneath Madeira exists in a similar way to the Canary Island hotspot and that regional mantle flow models for the region should be reassessed.</p><p>This is a contribution to project SIGHT (Ref. PTDC/CTA-GEF/30264/2017). The authors would like to acknowledge the financial support FCT through project UIDB/50019/2020 – IDL.</p>

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

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>

scholarly journals A rapid burst in hotspot motion through the interaction of tectonics and deep mantle flow

Nature ◽  
2016 ◽  
Vol 533 (7602) ◽  
pp. 239-242 ◽  
Author(s):  
Rakib Hassan ◽  
R. Dietmar Müller ◽  
Michael Gurnis ◽  
Simon E. Williams ◽  
Nicolas Flament
Keyword(s):  
Mantle Flow ◽  
Deep Mantle
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