These are some of the questions we will address in this chapter. Aubert et al. (2013) are in good agreement with a hybrid model of hydrogen-assisted conductivity where it is predicted that the conduction mechanism changes at a temperature of ~ 1300 K to conduction by two protons trapped at M-site and that high anisotropy is consistent with the observed anisotropy (Dai and Karato, 2014; Karato, 2013b). It is possible that this region has a low viscosity that might decouple convection current across the 410 km discontinuity. For example, smaller Rayleigh numbers and larger heat flux variation amplitudes promote a closer match and deeper penetration. A first-order model for the formation of the Earth's core assumes equilibrium conditions, where metal equilibrates with molten silicate in a deep magma ocean that could have extended well into the top of the Earth's lower mantle (pressures range from 28 to 45 GPa) in the early Earth assuming a homogenous accretion scenario (Li and Agee, 1996; O'Neill and Palme, 1998; Gessmann et al., 2001; Bouhifd and Jephcoat, 2003). Figure 3. Since the mantle evolves on timescales of tens of million years, its thermal structure can be regarded as stationary on typical dynamo timescales. SUBSCRIBE TO HAPPY LEARNING! The collapse of the protosolar cloud to form the sun produced a hot central region in the solar system and a considerable temperature gradient across it (Boss, 1998; Lewis, 1974). Earth's mantle is a layer of silicate rock between the crust and the outer core.It has a mass of 4.01 × 10 24 kg and thus makes up 67% of the mass of Earth. If they do not penetrate the 660-km discontinuity, the upper mantle may convect separately from the lower mantle, whereas if they sink to the base of the mantle, whole-mantle convection is probable. (2000) and Kutzner and Christensen (2004) show that the tomographic heat flux pattern promotes a concentration at the same bands identified in the paleomagnetic data. The seismologically observed changes in density and sound wave velocities, for example, are significantly (2–3 times) greater than those across the air–rock (or air–seawater) interface at the Earth's surface. C. Jaupart, ... J.-C. Mareschal, in Treatise on Geophysics (Second Edition), 2015. A thermal boundary layer exists above the core–mantle boundary, which is therefore a likely plume source depth. The upper mantle is separated from the crust by the Mohorovicic discontinuity or Moho. If the Earth had a significant gaseous envelope surrounding it throughout most of its accretion, it would have enhanced the chances of the upper portion of the mantle being wholly molten through thermal blanketing and greenhouse heating of the surface. Using these numbers, we can solve for slab velocity w = fQ/(ρcpΔTδ2πR) ≈ 10 cm year− 1, which is precisely the typical velocity for fast, active plates and predicted by slab-pull arguments (Section 7.07.4.1.1). If ridge and hotspot are less than a few hundred kilometres apart, eruption of volcanics may occur at the ridge rather than, or in addition to, directly above the plume. These broad, warm regions of mantle, known as “mantle upwellings” are relatively buoyant and rise, providing the return flow. (2007) used numerical dynamo simulations to explore the influence of different cmb heat flux patterns on the fluid motion at the top of the free stream, that is, just underneath the Ekman boundary layer. The Earth's mantle plays an important role in the evolution of the crust and provides the thermal and mechanical driving forces for plate tectonics. The earth crust is subdivided into several dishes, and these plates glide over the mantle, and this is due to the intense heat that arises from the middle of … There will, therefore, be a positive gravity anomaly over rising mantle material and a negative gravity anomaly where mantle is cool and sinking (Figure 3). In fact, Raj (1975) and Lifshitz and Shikin (1965) explained transient fast strain rate (by a factor of ~ 5–10) by such a transient stress state. In summary, I conclude that although partial melting is ubiquitous in the Earth's mantle due to the presence of volatile elements, partial melting is unlikely to affect physical properties (seismic wave velocities, electrical conductivity, and rheological properties) so much because melt does not completely wet grain boundaries and the melt fraction is small (< 0.1%).
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