Paul J. Tackley

Bio: Paul J. Tackley is an academic researcher from ETH Zurich. The author has contributed to research in topics: Mantle convection & Mantle (geology). The author has an hindex of 65, co-authored 246 publications receiving 11999 citations. Previous affiliations of Paul J. Tackley include University of California & École Polytechnique Fédérale de Lausanne.

Effects of an endothermic phase transition at 670 km depth in a spherical model of convection in the Earth's mantle

Abstract: Numerical modelling of mantle convection in a spherical shell with an endothermic phase change at 670 km depth reveals an inherently three-dimensional flow pattern, containing cylindrical plumes and linear sheets which behave differently in their ability to penetrate the phase change. The dynamics are dominated by accumulation of downwelling cold material above 670 km depth, resulting in frequent avalanches of upper-mantle material into the lower mantle. This process generates long-wavelength lateral heterogeneity, helping to resolve the contradiction between seismic tomographic observations and expectations from mantle convection simulations.

Mantle Convection and Plate Tectonics: Toward an Integrated Physical and Chemical Theory

Abstract: Plate tectonics and convection of the solid, rocky mantle are responsible for transporting heat out of Earth. However, the physics of plate tectonics is poorly understood; other planets do not exhibit it. Recent seismic evidence for convection and mixing throughout the mantle seems at odds with the chemical composition of erupted magmas requiring the presence of several chemically distinct reservoirs within the mantle. There has been rapid progress on these two problems, with the emergence of the first self-consistent models of plate tectonics and mantle convection, along with new geochemical models that may be consistent with seismic and dynamical constraints on mantle structure.

Self-consistent generation of tectonic plates in time-dependent, three-dimensional mantle convection simulations

Abstract: [1] Presented here are self-consistent, three-dimensional simulations of mantle convection, some of which display an approximation of plate tectonic behavior that is continuous in space and time. Plate behavior arises through a reasonable material description of silicate deformation, with a simple yield stress being sufficient to give first-order plate-like behavior; however, the required yield strength or fault frictional coefficient is much less than experimentally determined values. Toroidal:poloidal ratios are within geologically observed limits. The sensitivity of the system to yield strength and the form of strength envelope is systematically investigated. Optimum plate character is obtained in a narrow range of yield strength, below which diffuse boundaries, and above which episodic behavior, and eventually a rigid lid, are observed. Models with mobile lids develop very long wavelength horizontal structure, the longest wavelength possible in the domain. Two-dimensional models display much greater time dependence than three-dimensional models.

A doubling of the post-perovskite phase boundary and structure of the Earth's lowermost mantle

Abstract: A new model of the deep Earth allows geophysicists to measure variations in Earth's temperature near the boundary between the rocky mantle and core. Using a recently discovered phase change in the lowest part of the Earth's mantle, where atoms rearrange themselves in crystals under extreme pressure and temperature, the model also explains odd features of this part of the mantle, such as patchy regions that reflect seismic waves generated by large earthquakes and inferences of dense partial melting. Combined with observations, the results imply very large variations in temperature, providing further evidence for circulation of material throughout the Earth's mantle. The thermal structure of the Earth's lowermost mantle—the D″ layer spanning depths of ∼2,600–2,900 kilometres1—is key to understanding the dynamical state and history of our planet. Earth's temperature profile (the geotherm) is mostly constrained by phase transitions, such as freezing at the inner-core boundary or changes in crystal structure within the solid mantle, that are detected as discontinuities in seismic wave speed and for which the pressure and temperature conditions can be constrained by experiment and theory. A recently discovered phase transition at pressures of the D″ layer2,3,4 is ideally situated to reveal the thermal structure of the lowermost mantle, where no phase transitions were previously known to exist. Here we show that a pair of seismic discontinuities observed in some regions of D″ can be explained by the same phase transition as the result of a double-crossing of the phase boundary by the geotherm at two different depths. This simple model can also explain why a seismic discontinuity is not observed in some other regions, and provides new constraints for the magnitude of temperature variations within D″.

Light-induced shape-memory polymers

Abstract: Materials are said to show a shape-memory effect if they can be deformed and fixed into a temporary shape, and recover their original, permanent shape only on exposure to an external stimulus. Shape-memory polymers have received increasing attention because of their scientific and technological significance. In principle, a thermally induced shape-memory effect can be activated by an increase in temperature (also obtained by heating on exposure to an electrical current or light illumination). Several papers have described light-induced changes in the shape of polymers and gels, such as contraction, bending or volume changes. Here we report that polymers containing cinnamic groups can be deformed and fixed into pre-determined shapes--such as (but not exclusively) elongated films and tubes, arches or spirals--by ultraviolet light illumination. These new shapes are stable for long time periods, even when heated to 50 degrees C, and they can recover their original shape at ambient temperatures when exposed to ultraviolet light of a different wavelength. The ability of polymers to form different pre-determined temporary shapes and subsequently recover their original shape at ambient temperatures by remote light activation could lead to a variety of potential medical and other applications.

Large igneous provinces: crustal structure, dimensions, and external consequences

Abstract: Large igneous provinces (LIPs) are a continuum of voluminous iron and magnesium rich rock emplacements which include continental flood basalts and associated intrusive rocks, volcanic passive margins, oceanic plateaus, submarine ridges, seamount groups, and ocean basin flood basalts Such provinces do not originate at “normal” seafloor spreading centers We compile all known in situ LIPs younger than 250 Ma and analyze dimensions, crustal structures, ages, and emplacement rates of representatives of the three major LIP categories: Ontong Java and Kerguelen-Broken Ridge oceanic plateaus, North Atlantic volcanic passive margins, and Deccan and Columbia River continental flood basalts Crustal thicknesses range from 20 to 40 km, and the lower crust is characterized by high (70-76 km s?1) compressional wave velocities Volumes and emplacement rates derived for the two giant oceanic plateaus, Ontong Java and Kerguelen, reveal short-lived pulses of increased global production; Ontong Java’s rate of emplacement may have exceeded the contemporaneous global production rate of the entire mid-ocean ridge system The major part of the North Atlantic volcanic province lies offshore and demonstrates that volcanic passive margins belong in the global LIP inventory Deep crustal intrusive companions to continental flood volcanism represent volumetrically significant contributions to the crust We envision a complex mantle circulation which must account for a variety of LIP sizes, the largest originating in the lower mantle and smaller ones developing in the upper mantle This circulation coexists with convection associated with plate tectonics, a complicated thermal structure, and at least four distinct geochemical/isotopic reservoirs LIPs episodically alter ocean basin, continental margin, and continental geometries and affect the chemistry and physics of the oceans and atmosphere with enormous potential environmental impact Despite the importance of LIPs in studies of mantle dynamics and global environment, scarce age and deep crustal data necessitate intensified efforts in seismic imaging and scientific drilling in a range of such features

Evidence for deep mantle circulation from global tomography

Abstract: Seismic tomography based on P-wave travel times and improved earthquake locations provides further evidence for mantle-wide convective flow. The use of body waves makes it possible to resolve long, narrow structures in the lower mantle some of which can be followed to sites of present-day plate convergence at the Earth's surface. The transition from subduction-related linear structures in the mid-mantle to long-wavelength heterogeneity near the core-mantle boundary remains enigmatic, but at least some slab segments seem to sink to the bottom of the mantle.

Particle-in-Cell Charged Particle Simulations, plus Monte Carlo Collisions with Neutral Atoms, PIC-MCC

Abstract: Many-particle charged-particle plasma simulations using spatial meshes for the electromagnetic field solutions, particle-in-cell (PIC) merged with Monte Carlo collision (MCC) calculations, are coming into wide use for application to partially ionized gases. The author emphasizes the development of PIC computer experiments since the 1950s starting with one-dimensional (1-D) charged-sheet models, the addition of the mesh, and fast direct Poisson equation solvers for 2-D and 3-D. Details are provided for adding the collisions between the charged particles and neutral atoms. The result is many-particle simulations with many of the features met in low-temperature collision plasmas; for example, with applications to plasma-assisted materials processing, but also related to warmer plasmas at the edges of magnetized fusion plasmas. >