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Shijie Zhong - One of the best experts on this subject based on the ideXlab platform.
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Implementation and application of adaptive mesh refinement for thermochemical Mantle Convection studies
Geochemistry Geophysics Geosystems, 2011Co-Authors: Wei Leng, Shijie ZhongAbstract:Numerical modeling of Mantle Convection is challenging. Owing to the multiscale nature of Mantle dynamics, high resolution is often required in localized regions, with coarser resolution being sufficient elsewhere. When investigating thermochemical Mantle Convection, high resolution is required to resolve sharp and often discontinuous boundaries between distinct chemical components. In this paper, we present a 2-D finite element code with adaptive mesh refinement techniques for simulating compressible thermochemical Mantle Convection. By comparing model predictions with a range of analytical and previously published benchmark solutions, we demonstrate the accuracy of our code. By refining and coarsening the mesh according to certain criteria and dynamically adjusting the number of particles in each element, our code can simulate such problems efficiently, dramatically reducing the computational requirements (in terms of memory and CPU time) when compared to a fixed, uniform mesh simulation. The resolving capabilities of the technique are further highlighted by examining plume‐induced entrainment in a thermochemical Mantle Convection simulation.
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Constraints on viscous dissipation of plate bending from compressible Mantle Convection
Earth and Planetary Science Letters, 2010Co-Authors: Wei Leng, Shijie ZhongAbstract:Abstract Tectonic plates on the Earth's surface bend at plate boundaries as they subduct into the Mantle, thus generating viscous dissipation. It has been proposed that viscous dissipation due to plate bending accounts for more than 40% of the total viscous dissipation in Mantle Convection. The proposed large bending dissipation at subduction zones may have significant effects on the Earth's thermal evolution history. However, recent studies show that viscous dissipation from plate bending may not be as significant as previously suggested. Here based on an energetics argument of Mantle Convection and previously estimated bending dissipation for present-day Earth's subduction zones, we show that the total dissipation in the Earth's Mantle is 10.0–15.5 TW and that the bending dissipation only accounts for
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Supercontinent formation from stochastic collision and Mantle Convection models
Gondwana Research, 2008Co-Authors: Nan Zhang, Shijie Zhong, Allen K. McnarmaraAbstract:article i nfo Article history: The large-scale tectonics in the last billion years (Ga) are predominated by the assembly and breakup of supercontinents Rodinia and Pangea. The mechanisms controlling the assembly of supercontinents are not clear. Here, we investigate the assembly of a supercontinent with 1) stochastic models of randomly-moving continental blocks and 2) 3-D spherical models of Mantle Convection with continental blocks. For the stochastic models, we determined the time required for all the blocks to assemble into a single supercontinent on a spherical surface. We found that the assembly time from our stochastic models is significantly longer than inferred for Pangea and Rodinia. However, our study also suggests that the assembly time from stochastic models is sensitive to the rules for randomly assigning continental motion in the models. In our dynamic models of Mantle Convection, continental blocks are modeled as deformable and compositionally distinct materials from the Mantle. We found that Mantle convective planform has significant effects on supercontinent assembly. For models with moderately strong lithosphere and the lower Mantle relative to the upper Mantle that lead to degree-1 Mantle Convection, continental blocks always assemble to a supercontinent in ∼250 million years (Ma) and this assembly time is consistent with inferred for Pangea and Rodinia. However, for models with intrinsically small-scale Mantle flows, we found that even when continental blocks merge to form a supercontinent, the assembly times are too long and the convective structures outside of supercontinent regions are of too small wavelengths, compared with observed. © 2008 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved.
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SC - Scalable adaptive Mantle Convection simulation on petascale supercomputers
2008 SC - International Conference for High Performance Computing Networking Storage and Analysis, 2008Co-Authors: Carsten Burstedde, Georg Stadler, Lucas C. Wilcox, Eh Tan, Michael Gurnis, Omar Ghattas, Shijie ZhongAbstract:Mantle Convection is the principal control on the thermal and geological evolution of the Earth. Mantle Convection modeling involves solution of the mass, momentum, and energy equations for a viscous, creeping, incompressible non-Newtonian fluid at high Rayleigh and Peclet numbers. Our goal is to conduct global Mantle Convection simulations that can resolve faulted plate boundaries, down to 1 km scales. However, uniform resolution at these scales would result in meshes with a trillion elements, which would elude even sustained petaflops supercomputers. Thus parallel adaptive mesh refinement and coarsening (AMR) is essential. We present RHEA, a new generation Mantle Convection code designed to scale to hundreds of thousands of cores. RHEA is built on ALPS, a parallel octree-based adaptive mesh finite element library that provides new distributed data structures and parallel algorithms for dynamic coarsening, refinement, rebalancing, and repartitioning of the mesh. ALPS currently supports low order continuous Lagrange elements, and arbitrary order discontinuous Galerkin spectral elements, on octree meshes. A forest-of-octrees implementation permits nearly arbitrary geometries to be accommodated. Using TACC's 579 teraflops Ranger supercomputer, we demonstrate excellent weak and strong scalability of parallel AMR on up to 62,464 cores for problems with up to 12.4 billion elements. With RHEA'S adaptive capabilities, we have been able to reduce the number of elements by over three orders of magnitude, thus enabling us to simulate large-scale Mantle Convection with finest local resolution of 1.5 km.
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Viscous heating, adiabatic heating and energetic consistency in compressible Mantle Convection
Geophysical Journal International, 2008Co-Authors: Wei Leng, Shijie ZhongAbstract:SUMMARY Although it has been suggested that the total viscous heating, Qv, should be exactly balanced by the total adiabatic heating, Qa, for compressible Mantle Convection, previous numerical studies show a significant imbalance of up to several percent between Qv and Qa for simple isoviscous compressible Convection. The cause of this imbalance and its potential effects on more complicated convective systems remain largely unknown. In this study, we present an analysis to show that total viscous heating and adiabatic heating for compressible Mantle Convection with anelastic liquid approximation (ALA) and the Adams–Williamson equation of state are balanced out at any instant in time, and that the previously reported imbalance between Qv and Qa for numerical models with a truncated anelastic liquid approximation (TALA) is caused by neglecting the effect of the pressure on the buoyancy force. Although we only consider the Adams–Williamson equation of state in our analysis, our method can be used to check the energetic consistency for other forms of equation of state. We formulate numerical models of compressible Mantle Convection under both TALA and ALA formulations by modifying the Uzawa algorithm in Citcom code. Our numerical results confirm our analysis on the balance between total viscous heating and total adiabatic heating.
John Huw Davies - One of the best experts on this subject based on the ideXlab platform.
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Influence of the Ringwoodite-Perovskite transition on Mantle Convection in spherical geometry as a function of Clapeyron slope and Rayleigh number
Solid Earth, 2011Co-Authors: Martin Wolstencroft, John Huw DaviesAbstract:Abstract. We investigate the influence on Mantle Convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase Mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P) and the vigour of Convection (as measured by the Rayleigh number, Ra) on Mantle Convection. We have undertaken 76 simulations of isoviscous Mantle Convection in spherical geometry, varying Ra and P. Three domains of behaviour were found: layered Convection for high Ra and more negative P, whole Mantle Convection for low Ra and less negative P, and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = α Raβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole Mantle Convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra ≈ 2.5 × 104 (well below Earth Mantle vigour) and P a −0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that Convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.
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Influence of the Ringwoodite-Perovskite transition on Mantle Convection in spherical geometry as a function of Clapeyron slope and Rayleigh number
2011Co-Authors: Martin Wolstencroft, John Huw DaviesAbstract:Abstract. We investigate the influence on Mantle Convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase Mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P) and the vigour of Convection (as measured by the Rayleigh number, Ra) on Mantle Convection. We have undertaken 76 simulations of isoviscous Mantle Convection in spherical geometry varying Ra and P. Three domains of behaviour were found: layered Convection for high Ra and more negative P, whole Mantle Convection for low Ra and less negative P and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = αRaβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole Mantle Convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra≈2.5×104 and P≈−0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that Convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.
Don L. Anderson - One of the best experts on this subject based on the ideXlab platform.
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The scales of Mantle Convection
Tectonophysics, 1998Co-Authors: Don L. AndersonAbstract:Seismic, topographic and gravity data show that there are two important scales of Mantle Convection. These are associated with spherical harmonic degrees l=2 and 6. The l=2 pattern corresponds to the pattern of subduction cooling since the breakup of Pangea. Most hotspots and ridges occur in the half of the globe unaffected by this cooling and all large igneous provinces were generated over this part of the Mantle. The l=2 distribution of upwellings and downwellings is likely to be a long-lived feature of the Earth; cold regions of the Mantle repeatedly attract continents and subduction reinforces the coldness. An l=1 pattern of Convection is probably related to supercontinents and their breakup. Degree 6 Convection shows up in the spectrum of hotspots and upper Mantle tomography and in the correlation of tomography and topography with the geoid. Cratons, with their deep cold keels, control the l=6 pattern, and may even cause it, by their role in establishing lateral temperature gradients and relief at the top of the convecting Mantle. Subduction zones reinforce the craton pattern. Downwellings preferentially occur under cratons; upwellings, and hotspots, occur at complementary locations. Supercontinents, and their associated subduction zones (l=1) constantly assemble and reassemble in the African-Atlantic hemisphere and the continental fragments, in the dispersed state, periodically settle into the polar band of geoid lows (l=2 and 6) that now includes the Americas, Antarctica, Australia and India. If cratons control the l=6 pattern of Convection (and many patterns of l=6 are possible; e.g., sectoral, zonal, checker-board) then upper-Mantle Convection may reorganize roughly every 30 Ma as cratons move about. The hotspot spectrum is probably related to lithospheric extension as well as to broad upwellings. A third and smaller scale of Convection, order 400–1000 km in dimension, is just below the resolution of global tomography but shows up in the gravity field (geoid) and topography. This scale is controlled by the depth of an endothermic phase change which tends to stratify Mantle Convection, and the thickness of the upper Mantle low viscosity zone. Convective domains of this dimension are also implied by the scales of chemical homogeneity, lengths of rifts, ridges and seamount chains, fracture zone spacing and mid-ocean ridge segmentation. The temperature, geochemistry and fertility of these upper-Mantle scale domains is controlled by their previous history of subduction, continental insulation or refrigeration, and processing by ridges. Fertile, or volatile-rich, or hot, cells can be mistaken for plumes. Hotspot swells are typically of the dimension that we argue is a characteristic upper Mantle scale rather than a deep Mantle plume scale. Geochemical domains of various sizes exist in the upper Mantle. They are broad-scale features, rather than point sources, as in plume theories. Lithospheric dynamics and geometric focusing, not Mantle dynamics, control the dimensions of so-called hotspot eruptives.
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Layered Mantle Convection: A model for geoid and topography
Earth and Planetary Science Letters, 1997Co-Authors: Lianxing Wen, Don L. AndersonAbstract:The long-wavelength geoid and topography are dynamic effects of a convecting Mantle. The long-wavelength geoid of the Earth is controlled by density variations in the Mantle and has been explained by circulation models involving whole Mantle flow. However, the relationship of long-wavelength topography to Mantle circulation has been a puzzling problem in geodynamics. We show that the dynamic topography is mainly due to density variations in the upper Mantle, even after the effects of lithospheric cooling and crustal thickness variation are taken into account. Layered Mantle Convection, with a shallow origin for surface dynamic topography, is consistent with the spectrum, small amplitude and pattern of the topography. Layered Mantle Convection, with a barrier about 250 km deeper than the 670 km phase boundary, provides a self-consistent geodynamic model for the amplitude and pattern of both the long-wavelength geoid and surface topography.
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Top-driven asymmetric Mantle Convection
Geological Society of America Special Papers, 1Co-Authors: Carlo Doglioni, Don L. AndersonAbstract:The role of decoupling in the low-velocity zone is crucial for understanding plate tectonics and Mantle Convection. Mantle Convection models fail to integrate plate kinematics and thermodynamics of the Mantle. In a first gross estimate, we computed at >300 km^3/yr the volume of the plates lost along subduction zones. Mass balance predicts that slabs are compensated by broad passive upwellings beneath oceans and continents, passively emerging at oceanic ridges and backarc basins. These may correspond to the broad low-wavespeed regions found in the upper Mantle by tomography. However, west-directed slabs enter the Mantle more than three times faster (~232 km^3/yr) than in the opposite east- or northeast-directed subduction zones (~74 km^3/yr). This difference is consistent with the westward drift of the outer shell relative to the underlying Mantle, which accounts for the steep dip of west-directed slabs, the asymmetry between flanks of oceanic ridges, and the directions of ridge migration. The larger recycling volumes along west-directed subduction zones imply asymmetric cooling of the underlyingMantle and that there is an “easterly” directed component of the upwelling replacement Mantle. In this model, Mantle Convection is tuned by polarized decoupling of the advecting and shearing upper boundary layer. Return Mantleflow can result from passive volume balance rather than only by thermal buoyancy-driven upwelling.
Martin Wolstencroft - One of the best experts on this subject based on the ideXlab platform.
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Influence of the Ringwoodite-Perovskite transition on Mantle Convection in spherical geometry as a function of Clapeyron slope and Rayleigh number
Solid Earth, 2011Co-Authors: Martin Wolstencroft, John Huw DaviesAbstract:Abstract. We investigate the influence on Mantle Convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase Mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P) and the vigour of Convection (as measured by the Rayleigh number, Ra) on Mantle Convection. We have undertaken 76 simulations of isoviscous Mantle Convection in spherical geometry, varying Ra and P. Three domains of behaviour were found: layered Convection for high Ra and more negative P, whole Mantle Convection for low Ra and less negative P, and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = α Raβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole Mantle Convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra ≈ 2.5 × 104 (well below Earth Mantle vigour) and P a −0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that Convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.
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Influence of the Ringwoodite-Perovskite transition on Mantle Convection in spherical geometry as a function of Clapeyron slope and Rayleigh number
2011Co-Authors: Martin Wolstencroft, John Huw DaviesAbstract:Abstract. We investigate the influence on Mantle Convection of the negative Clapeyron slope ringwoodite to perovskite and ferro-periclase Mantle phase transition, which is correlated with the seismic discontinuity at 660 km depth. In particular, we focus on understanding the influence of the magnitude of the Clapeyron slope (as measured by the Phase Buoyancy parameter, P) and the vigour of Convection (as measured by the Rayleigh number, Ra) on Mantle Convection. We have undertaken 76 simulations of isoviscous Mantle Convection in spherical geometry varying Ra and P. Three domains of behaviour were found: layered Convection for high Ra and more negative P, whole Mantle Convection for low Ra and less negative P and transitional behaviour in an intervening domain. The boundary between the layered and transitional domain was fit by a curve P = αRaβ where α = −1.05, and β = −0.1, and the fit for the boundary between the transitional and whole Mantle Convection domain was α = −4.8, and β = −0.25. These two curves converge at Ra≈2.5×104 and P≈−0.38. Extrapolating to high Ra, which is likely earlier in Earth history, this work suggests a large transitional domain. It is therefore likely that Convection in the Archean would have been influenced by this phase change, with Earth being at least in the transitional domain, if not the layered domain.
R. D. Mueller - One of the best experts on this subject based on the ideXlab platform.
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On the Scales of Dynamic Topography in Whole-Mantle Convection Models
Geochemistry Geophysics Geosystems, 2018Co-Authors: Maelis Arnould, Nicolas Coltice, N. Flament, V. Seigneur, R. D. MuellerAbstract:Mantle Convection shapes Earth's surface by generating dynamic topography. Observational constraints and regional Convection models suggest that surface topography could be sensitive to Mantle flow for wavelengths as short as 1,000 and 250 km, respectively. At these spatial scales, surface processes including sedimentation and relative sea-level change occur on million-year timescales. However, time-dependent global Mantle flow models do not predict small-scale dynamic topography yet. Here we present 2-D spherical annulus numerical models of Mantle Convection with large radial and lateral viscosity contrasts. We first identify the range of Rayleigh number, internal heat production rate and yield stress for which models generate plate-like behavior, surface heat flow, surface velocities, and topography distribution comparable to Earth's. These models produce both whole-Mantle Convection and small-scale Convection in the upper Mantle, which results in small-scale (\textless500 km) to large-scale (\textgreater10(4) km) dynamic topography, with a spectral power for intermediate scales (500 to 10(4) km) comparable to estimates of present-day residual topography. Timescales of Convection and the associated dynamic topography vary from five to several hundreds of millions of years. For a Rayleigh number of 10(7), we investigate how lithosphere yield stress variations (10-50 MPa) and the presence of deep thermochemical heterogeneities favor small-scale (200-500 km) and intermediate-scale (500-10(4) km) dynamic topography by controlling the formation of small-scale Convection and the number and distribution of subduction zones, respectively. The interplay between Mantle Convection and lithosphere dynamics generates a complex spatial and temporal pattern of dynamic topography consistent with constraints for Earth.