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  • 1
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Geophysical journal international 126 (1996), S. 0 
    ISSN: 1365-246X
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Chemical differentiation and convective removal of internal heat make the Earth's lithosphere a thermal and a chemical boundary layer. Thin layers of chemically light material form near the Earth's surface and become embedded within the cold thermal boundary layer associated with interior heat removal. The likelihood of near-surface thermal and chemical boundary layer interactions influencing the Earth's thermotectonic evolution prompts the models presented herein. A simplified system, consisting of a chemically light layer within the upper thermal boundary layer of a denser thermally convecting layer, is explored through a suite of numerical experiments to see how its dynamic behaviour differs from similar, well-studied, thermal boundary layer systems. A major cause of differences between the two systems resides in the ability of the deformable near-surface chemical layer to alter the effective upper thermal boundary condition imposed on the convectively unstable layer below. In thermal equilibrium, regions of chemical boundary layer accumulation locally enforce an effectively near-constant heat-flux condition on the thermally convecting layer due to the finite thermal conductivity of chemical boundary layer material. For cases in which chemical accumulations translate laterally above the unstable layer, the thermal coupling condition between chemical boundary layer material and the unstable layer below is one of non-equilibrium type, i.e. the thermal condition at the top of the convectively unstable layer is time-, as well as space-, variable. A second major cause of differences is that, for the thermal/chemical system, chemically induced rheologic variations can offset, or compete with, those due to temperature. More specifically, the presence of chemically weak material can lubricate convective downwellings allowing for enhanced overturn of an, on average, strong upper thermal boundary layer. Both of these factors have low-order effects on internal flow structure and heat loss and lead to dynamic behaviour in which chemical boundary layer deformation is not only driven by flow in the thermally convecting interior layer but also feeds back and alters this flow. Some implications of this, in regard to elucidating how near-surface chemical boundary layer deformation, e.g. continental tectonics, might interact with, and influence, mantle convection, are discussed.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    [s.l.] : Nature Publishing Group
    Nature 378 (1995), S. 709-711 
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] The behaviour shown in Fig. 1 has previously been interpreted as evidence of additional heat input into the base of old continental lithosphere due to a secondary scale of convection-that is, one of a smaller scale than that associated directly with the formation of tectonic plates at mid-ocean ...
    Type of Medium: Electronic Resource
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  • 3
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    In:  Earth planet. Sci. Lett., Edmonton, Conseil de l'Europe, vol. 150, no. 3-4, pp. 233-243, pp. B10410, (ISSN: 1340-4202)
    Publication Date: 1997
    Keywords: Modelling ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Gravimetry, Gravitation ; Plate tectonics ; ConvolutionE ; Three dimensional ; mantle ; isostasy ; continents ; Mohorovicic ; discontinuity ; orogeny ; gravity ; anomalies ; tectonics
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  • 4
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    In:  J. Geophys. Res., Luxembourg, Conseil de l'Europe, vol. 100, no. 1-3, pp. 15193-15203, pp. B02405, (ISSN: 1340-4202)
    Publication Date: 1995
    Keywords: China ; Plate tectonics ; Tectonics ; Geol. aspects ; JGR
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  • 5
    Publication Date: 2016-05-12
    Description: We use 1D thermal history models and 3D numerical experiments to study the impact of dynamic thermal disequilibrium and large temporal variations of normal and shear stresses on the initiation of plate tectonics. Previous models that explored plate tectonics initiation from a steady state, single plate mode of convection concluded that normal stresses govern the initiation of plate tectonics, which based on our 1D model leads to plate yielding being more likely with increasing interior heat and planet mass for a depth-dependent Byerlee yield stress. Using 3D spherical shell mantle convection models in an episodic regime allows us to explore larger temporal stress variations than can be addressed by considering plate failure from a steady state stagnant lid configuration. The episodic models show that an increase in convective mantle shear stress at the lithospheric base initiates plate failure, which leads with our 1D model to plate yielding being less likely with increasing interior heat and planet mass. In this out-of-equilibrium and strongly time-dependent stress scenario, the onset of lithospheric overturn events cannot be explained by boundary layer thickening and normal stresses alone. Our results indicate that in order to understand the initiation of plate tectonics, one should consider the temporal variation of stresses and dynamic disequilibrium.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2019
    Description: Abstract Thermal history models, historically used to understand Earth's geologic history, are being coupled to climate models to map conditions that allow planets to maintain life. However, the lack of structural uncertainty assessment has blurred guidelines for how thermal history models can be used toward this end. Structural uncertainty is intrinsic to the modeling process. Model structure refers to the cause and effect relations that define a model and are assumed to adequately represent a particular real world system. Intrinsic/structural uncertainty is different from input and parameter uncertainties (which are often evaluated for thermal history models). A full uncertainty assessment requires that input/parametric and intrinsic/structural uncertainty be evaluated (one is not a substitute for the other). We quantify the intrinsic uncertainty for several parameterized thermal history models (a subclass of planetary models). We use single perturbation analysis to determine the reactance time of different models. This provides a metric for how long it takes low‐amplitude, unmodeled effects to decay or grow. Reactance time is shown to scale inversely with the strength of the dominant model feedback (negative or positive). A perturbed physics analysis is then used to determine uncertainty shadows for model outputs. This provides probability distributions for model predictions. It also tests the structural stability of a model (do model predictions remain qualitatively similar, and within assumed model limits, in the face of intrinsic uncertainty?). Once intrinsic uncertainty is accounted for, model outputs/predictions and comparisons to observational data should be treated in a probabilistic way.
    Print ISSN: 2169-9097
    Electronic ISSN: 2169-9100
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
    Publication Date: 2015-10-10
    Description: Consideration of the structure of dynamical equilibria in terrestrial planets using simplified descriptions of the relevant heat transport processes (rigid-lid convection, plate tectonics, heat-pipe volcanism) reveals that if the efficiency of plate-tectonic heat transport decreases at higher mantle temperature, then it cannot govern quasi-equilibrium dynamical evolution, and the system is always evolving away from the plate-tectonic regime. A planet on which plate tectonics is less efficient at higher temperature stays in heat-pipe mode longer, spends less time undergoing plate tectonics, and has a low and ever-decreasing Urey number during this phase. These conclusions are based solely on the structure of the equilibria in a system with less efficient plate tectonics in the past and are independent of the mechanisms leading to this behavior. Commonly used quasi-equilibrium approaches to planetary thermal evolution are likely not valid for planets in which heat transport becomes less efficient at higher temperature.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
    Publication Date: 2016-08-30
    Description: The discovery of large terrestrial (~1 Earth mass (M e ) to 〈 10 M e ) extrasolar planets has prompted a debate as to the likelihood of plate tectonics on these planets. Canonical models assume classic basal heating scaling relationships remain valid for mixed heating systems with an appropriate internal temperature shift. Those scalings predict a rapid increase of convective velocities ( V rms ) with increasing Rayleigh numbers ( Ra ) and non-dimensional heating rates ( Q ). To test this we conduct a sweep of 3-D numerical parameter space for mixed heating convection in isoviscous spherical shells. Our results show that while V rms increases with increasing thermal Ra it does so at a slower rate than predicted by bottom heated scaling relationships. Further, the V rms decreases asymptotically with increasing Q . These results show that independent of specific rheologic assumptions (e.g., viscosity formulations, water effects, lithosphere yielding), the differing energetics of mixed and basally heated systems can explain the discrepancy between different modeling groups. High temperature, or young, planets with a large contribution from internal heating will operate in different scaling regimes compared to cooler temperature, or older, planets that may have a larger relative contribution from basal heating. Thus, differences in predictions as to the likelihood of plate tectonics on exoplanets may well result from different models being more appropriate to different times in the thermal evolution of a terrestrial planet (as opposed to different rheologic assumptions as has often been assumed).
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2016-08-27
    Description: We use a suite of 3-D numerical experiments to test and expand 2-D planar isoviscous scaling relationships of Moore [ 2008 ] for mixed heating convection in spherical geometry mantles. The internal temperature scaling of Moore [ 2008 ], when modified to account for spherical geometry, matches our experimental results to a high degree of fit. The heatflux through the boundary layers scale as a linear combination of internal (Q) and basal heating and the modified theory predictions match our experimental results. Our results indicate that boundary layer thickness and surface heat flux are not controlled by a local boundary layer stability condition (in agreement with the results of Moore [ 2008 ]), and are instead strongly influenced by boundary layer interactions. Subadiabtic mantle temperature gradients, in spherical 3D, are well described by a vertical velocity scaling based on discrete drips as opposed to a scaling based on coherent sinking sheets, which was found to describe 2D planar results. Root Mean Square (RMS) velocities are asymptotic for both low Q and high Q, with a region of rapid adjustment between asymptotes for moderate Q. RMS velocities are highest in the low Q asymptote, and decrease as internal heating is applied. The scaling laws derived by Moore [ 2008 ], and extended here, are robust and highlight the importance of differing boundary layer processes acting over variable Q and moderate Ra.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 10
    Publication Date: 2016-06-02
    Description: Nature Geoscience 9, 417 (2016). doi:10.1038/ngeo2707 Authors: Cin-Ty A. Lee, Laurence Y. Yeung, N. Ryan McKenzie, Yusuke Yokoyama, Kazumi Ozaki & Adrian Lenardic
    Print ISSN: 1752-0894
    Electronic ISSN: 1752-0908
    Topics: Geosciences
    Published by Springer Nature
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