Читать книгу Mantle Convection and Surface Expressions - Группа авторов - Страница 15

When combined with mineral physics constraints, observations of seismic anisotropy in Earth’s mantle can be used to infer mantle flow patterns and understand material transport through the mantle. Thorsten Becker and Sergei Lebedev summarize seismic anisotropy observations made in the upper mantle and discuss their relation to laboratory measurements. It is shown that regional convection patterns can be resolved using anisotropy observations, but uncertainties remain and systematic relationships need to be further refined and established.

An essential regional component of mantle convection is the subduction and deep cycling of oceanic lithosphere. Indeed, the sinking of subducted slabs through the mantle is a key driver of mantle circulation and plate tectonics. Zhouchuan Huang and Dapeng Zhao discuss the analysis of seismic anisotropy in subduction zone settings that is used to infer deformation and flow patterns around subducting slabs in the upper mantle.

Subducted oceanic crust often descends deep into the mantle, commonly reaching the core–mantle boundary. Understanding the fate of subducted material and its chemical interaction with the surrounding mantle is pivotal to our understanding of deep Earth material cycles, the interpretation of geophysical heterogeneity, and the diversity of geochemical signatures found in surface rocks. Mingming Li reviews our understanding of the distribution, physical behavior and chemical interaction of subducted oceanic crust in the deep mantle that emerges by integrating evidence from different disciplines.

In regions where subducting slabs reach the core‐mantle boundary, they may cause deformation strong enough to induce seismic anisotropy, in a similar way as discussed above for the upper mantle. Andy Nowacki and Sanne Cottaar explore the potential and limitations of multidisciplinary approaches to infer deep mantle flow from recent observations of lowermost mantle seismic anisotropy.

While the downwelling limbs of mantle convection are commonly observed in seismic images, at least in some cases from the surface to the core–mantle boundary (see above), the nature of upwellings remains more under‐resolved and uncertain. However, while their existence has been highly debated for a long time, researchers now converge towards a consensus in terms of the sheer existence and nature of plume‐like upwellings. Jeroen Ritsema et al. report on the challenges involved in imaging mantle plumes by seismic methods. They conclude that the deployment of seismic receivers on the ocean floors would lead to a significant advancement in our ability to image the interior of our planet in general, and mantle plumes in particular.