The Experts below are selected from a list of 156 Experts worldwide ranked by ideXlab platform
Masao Nakada - One of the best experts on this subject based on the ideXlab platform.
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long term true polar wander of the earth including the effects of convective processes in the mantle and Continental Drift
Geophysical Journal International, 2008Co-Authors: Masao NakadaAbstract:SUMMARY Long-term true polar wander (TPW) of the Earth was examined by taking into account the effects of simplified convective processes in the Earth’s mantle and Continental Drift. The TPW, for a given viscoelastic earth model, is wholly determined by both the magnitude of non-forcing elements of moment of inertia (I 11, I 22 and I 33) and I 12 element of product of inertia, and the rates for forcing elements, dI 13/dt and dI 23/dt. The forcing rates are largely related to time-dependent convective processes in the mantle and also Continental Drift. In this study, I examined the TPW on a convecting mantle with oscillating moments of inertia, inferred from a convective process of alternating degree-one and degree-two structure changes of mantle convection by Zhongetal. (2007). In the phase for a relatively hydrostatic Earth, corresponding to largely degree-one planform, the predicted TPW is sensitive to the viscosity structure of the mantle, particularly to the lithospheric viscosity structure, and its magnitude may be larger than ∼30 ◦ even for the forcing rates with ∼10 30 kg m 2 Myr −1 related to Continental Drift (Dickman 1979). In the phase for a non-hydrostatic Earth characterized by largely degree-two planform such as for the present-day, however, the TPW is less sensitive to the viscosity structure, and its magnitude may be ∼10 ◦ at most. These results may provide quantitative constraints on examining relationship between rheological structure and convective processes in the mantle, Continental Drift and TPW.
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true polar wander associated with Continental Drift on a hypothetical earth
Earth Planets and Space, 2007Co-Authors: Masao NakadaAbstract:Long-term true polar wander of the Earth (TPW) has generally been discussed by taking into account con-vective processes in the mantle such as downgoing slabs and upwelling plumes. Here I examined a relationship between Continental Drift and TPW on a hypothetical Earth with no such convective processes in the mantle. I evaluated temporal changes in moments of inertia owing to Continental Drift during a period of ~250 Ma based on a paleogeographic reconstruction, in which I estimated the lateral density heterogeneities by factoring in the observed mean land elevation of continents and average age of the oceanic lithosphere. The predictions for a viscoelastic Earth model with plausible viscosity models indicate that the long-term TPW might have been affected by Continental Drift throughout Cenozoic and Mesozoic times, which has wholly proceeded by maintaining isostasy at a certain depth, as well as convective processes in the mantle.
T Rolf - One of the best experts on this subject based on the ideXlab platform.
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constraints on mantle viscosity structure from Continental Drift histories in spherical mantle convection models
Tectonophysics, 2017Co-Authors: T Rolf, Fabio A Capitanio, Paul J TackleyAbstract:Abstract Earth's continents Drift in response to the force balance between mantle flow and plate tectonics and actively change the plate-mantle coupling. Thus, the patterns of Continental Drift provide relevant information on the coupled evolution of surface tectonics, mantle structure and dynamics. Here, we investigate rheological controls on such evolutions and use surface tectonic patterns to derive inferences on mantle viscosity structure on Earth. We employ global spherical models of mantle convection featuring self-consistently generated plate tectonics, which are used to compute time-evolving Continental configurations for different mantle and lithosphere structures. Our results highlight the importance of the wavelength of mantle flow for Continental configuration evolution. Too strong short-wavelength components complicate the aggregation of large Continental clusters, while too stable very long wavelength flow tends to enforce compact supercontinent clustering without reasonable dispersal frequencies. Earth-like Continental Drift with episodic collisions and dispersals thus requires a viscosity structure that supports long-wavelength flow, but also allows for shorter-wavelength contributions. Such a criterion alone is a rather permissive constraint on internal structure, but it can be improved by considering Continental-oceanic plate speed ratios and the toroidal-poloidal partitioning of plate motions. The best approximation of Earth's recent tectonic evolution is then achieved with an intermediate lithospheric yield stress and a viscosity structure in which oceanic plates are ∼ 103 × more viscous than the characteristic upper mantle, which itself is ∼ 100–200 × less viscous than the lowermost mantle. Such a structure causes continents to move on average ∼ (2.2 ± 1.0) × slower than oceanic plates, consistent with estimates from present-day and from plate reconstructions. This does not require a low viscosity asthenosphere globally extending below Continental roots. However, this plate speed ratio may undergo strong fluctuations on timescales of several 100 Myr that may be linked to periods of enhanced Continental collisions and are not yet captured by current tectonic reconstructions.
Octavio Pucheriart - One of the best experts on this subject based on the ideXlab platform.
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the 15th international geological congress south africa 1929 the resurgence of wegener s Continental Drift theory
Episodes, 2013Co-Authors: Luis Felipe Mazadiegomartinez, Octavio PucheriartAbstract:The 15th International Geological Congress was held in South Africa in 1929. Many interesting issues were tackled, thanks to the development of geophysical techniques, ideas about magmatic differentiation, and the origin of the Karroo System, among others. The importance of the Congress from the point of view of the history of geology lies in the fact that an 'inflection point' occurred as regards thinking about the Continental Drift theory that had been proposed by Wegener a few years earlier. It can be said that the contributions of Du Toit allowed a deepening in the theoretical bases of this scientific hypothesis, which celebrated its first hundred years in 2012.
Kazunori Yoshizawa - One of the best experts on this subject based on the ideXlab platform.
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Continental Drift with deep cratonic roots
Annual Review of Earth and Planetary Sciences, 2021Co-Authors: Masaki Yoshida, Kazunori YoshizawaAbstract:The influence of the Continental lithosphere and its root (or keel) on the Continental Drift of Earth is a key element in the history of plate tectonics. Previous geodynamic studies of mantle flow ...
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Continental Drift with Deep Cratonic Roots
Annual Review of Earth and Planetary Sciences, 2020Co-Authors: Masaki Yoshida, Kazunori YoshizawaAbstract:The influence of the Continental lithosphere and its root (or keel) on the Continental Drift of Earth is a key element in the history of plate tectonics. Previous geodynamic studies of mantle flow suggested that the cratonic root is moderately mechanically coupled with the underlying mantle, and stable Continental Drift on Earth's timescales occurs when the effective viscosity contrast between the Continental lithosphere and the underlying mantle is approximately 103. Both geodynamics and seismological studies indicate that mechanically weak mobile belts (i.e., orogenic or suture zones) that surround cratons may play a role in the longevity of the cratonic lithosphere over geologically long timescales (i.e., over 1,000 million years) because they act as a buffer region against the high-viscosity cratons. Low-viscosity asthenosphere, characterized by slow seismic velocities, reduces the basal drag force acting on the cratonic root, which may also contribute to the longevity of the cratonic lithosphere. ▪ The role of the Continental lithosphere and its root on the Continental Drift is reviewed from recent geodynamic and seismological studies. ▪ The cratonic root is moderately mechanically coupled with the underlying mantle and deformed by mantle flow over geological timescales. ▪ Orogenic belts or suture zones that surround cratons act as a buffer to protect cratons and are essential for their longevity. ▪ Low-viscosity asthenosphere may reduce the basal drag acting on the cratonic root and also contribute to its stability and longevity. Expected final online publication date for the Annual Review of Earth and Planetary Sciences, Volume 49 is May 28, 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.
Kenji Kawai - One of the best experts on this subject based on the ideXlab platform.
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mantle convection with Continental Drift and heat source around the mantle transition zone
Gondwana Research, 2013Co-Authors: Hiroki Ichikawa, Masanori Kameyama, Kenji KawaiAbstract:Abstract Geological studies have suggested that a significant amount of crustal material has been lost from the surface due to delamination, Continental collision, and subduction at oceanic–Continental convergent margins. If so, then the subducted crustal materials are expected to be trapped in the mid-mantle due to the density difference from peridotitic materials induced by the phase transition from coesite to stishovite. In order to study the effect of the subducted granitic materials floating around the mantle transition zone, we conducted two-dimensional numerical experiments of mantle convection incorporating a Continental Drift with a heat source placed around the bottom of the mantle transition zone. The simulations deal with a time-dependent convection of fluid under the extended Boussinesq approximation in a model of a two-dimensional rectangular box with a height of 2900 km and a width of 11,600 km, where a continent with a length of 2900 km and heat source below the continent are imposed. We found that the addition of heat source in the mantle transition zone considerably enhances the onset of upwelling plumes in the upper mantle, which further reduces the time scale of Continental Drift. The heat source also causes massive mechanical mixing, especially in the upper mantle. The results suggest that the heat source floating around the mantle transition zone can be a possible candidate for inducing the supercontinent cycle.