scholarly journals The Eternal Nile Is Even More Ancient Than We Thought

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Mary Morton
Keyword(s):  
Mantle Flow ◽  
Deep Mantle

Deep-mantle flow helps maintain the river’s steady course.

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 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

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.

Deep Mantle Dynamics in East Asia: Numerical Simulation of Mantle Convection Based on Seismic Tomography

2020 ◽  
Author(s):  
Huai Zhang ◽  
Qunfan Zheng ◽  
Zhen Zhang
Keyword(s):  
East Asia ◽  
Seismic Tomography ◽  
Upper Mantle ◽  
Continental Collision ◽  
Indian Plate ◽  
Mantle Flow ◽  
Lithospheric Deformation ◽  
Mantle Dynamics ◽  
Asthenospheric Mantle ◽  
Deep Mantle

<p>East Asia is a tectonically active area on earth and has a complicated lithospheric deformation due to the western continental collision from the cratonic Indian plate and the eastern oceanic subduction mainly from Pacific plate. Studies have suggested that the Indo–Asian continental collision may have driven significant lateral mantle flow, but the velocity, range and effect of the mantle flow remain uncertain. Hence, a series of 3-D numerical models are conducted in this study to reveal the impacts of the Indo–Asian collision on mantle dynamics beneath the East Asia, especially on the asthenospheric mantle. Global model domain encompasses the lithosphere, upper mantle and the lower mantle with different viscosity for each layer. A global temperature structure built from seismic tomography and absolute plate field are applied subsequently to get a better constraint of the initial temperature condition and surficial velocity boundary condition. Thus, the reasonable velocity and temperature distributions of upper mantle beneath East Asia at different depths are retrieved based on our 3-D global mantle flow simulations, and the key controlling parameters in shaping the present-day observed mantle structure are investigated. The results show different scales of convection beneath East Asia.</p><p>Our results suggest that Indo–Asian collision may have induced mantle flow beneath the Indian plate and the different velocity structures between the asthenosphere and lithosphere indicate the shear drag of asthenospheric mantle. That may explain the reason that Indo–Asian collision has occurred since 50 Ma, and this collision can still continue to accelerate in the Tibetan Plateau. The simulation results also show the lithospheric delamination and the induced mantle upwelling, which is consistent with the general understanding from previous observations. The Indian lithosphere and its asthenosphere move northward, while the Yunnan lithosphere and its asthenosphere move southward, that may reflect the differences in deep mantle dynamics between the eastern and western Himalayan Syntaxis.</p>

scholarly journals The deep Earth origin of the Iceland plume and its effects on regional surface uplift and subsidence

2016 ◽  
Author(s):  
N. Barnett-Moore ◽  
R. Hassan ◽  
N. Flament ◽  
R. D. Müller
Keyword(s):  
North Atlantic ◽  
Flow Model ◽  
Mantle Flow ◽  
Seismic Structure ◽  
Dynamic Topography ◽  
The North ◽  
Deep Mantle ◽  
Deep Earth ◽  
The North Atlantic ◽  
Iceland Plume

Abstract. The present-day seismic structure of the mantle under the North Atlantic indicates that the Iceland hotspot represents the surface expression of a deep mantle plume, which is thought to have erupted in the North Atlantic during the Paleocene. The spatial and temporal evolution of the plume since its eruption is still highly debated, and little is known about its deep mantle history. Here, a paleogeographically constrained global mantle flow model is used to investigate the evolution of deep Earth flow and surface dynamic topography in the North Atlantic since the Jurassic. The model shows that over the last ~ 100 Myr a remarkably stable pattern of convergent flow has prevailed in the lowermost mantle near the tip of the African Large Low-Shear Velocity Province (LLSVP), making it an ideal plume nucleation site. The present-day location of the model plume is ~ 10° southeast from the inferred present-day location of the Iceland plume. We apply a constant surface rotation to the model through time, derived from correcting for this offset at present-day. A comparison between the rotated model dynamic topography evolution and available offshore geological and geophysical observations across the region confirms that a widespread episode of Paleocene transient uplift followed by early Eocene anomalous subsidence can be explained by the mantle-driven effects of a plume head ~ 2000 km in diameter, arriving beneath central western Greenland during the Paleocene. The rotated model plume eruption location beneath Western Greenland is compatible with previous models. The mantle flow model underestimates the magnitude of observed anomalous subsidence during the Paleocene in some parts of the North Atlantic by as much as several hundred meters, which we attribute to upper mantle convection processes, not captured by the model.

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.

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