understanding of rapid geological processes are an entirely new dimension for earth scientists to explore, with computers now making it possible.

Modern Geological Maps

Maps constitute an important data base in the solid-earth sciences. Field relations must be continually reexamined in the light of new theoretical concepts, and no substitute exists for continuing geological mapping and analysis of relations in the field. Maps should include three-dimensional data on geophysics and geochemistry and data from satellite-based remote sensing. Digitizing the different data sets that are to be used together is essential.

Research Area V: Dynamics of the Core and Mantle

Origin of the Magnetic Field

Magnetic field generation is one of the universal processes in the cosmos, and the outstanding unsolved geophysical problem involving the core is generation of the geomagnetic field. Important advances in the near future will concentrate on more limited problems such as (a) the origin of the dipole inclination, secular variation, and the westward drift; (b) the role of the mantle in influencing magnetic field structure; and (c) a determination of the power source driving the dynamo.

Core-Mantle Boundary

With the deployment of a new broadband digital network of seismometers, the likelihood of deciphering the nature of the core-mantle boundary is excellent. There is the prospect that geomagnetic anomalies can be associated with seismological heterogeneities found at the base of the mantle, leading to the possibility of documenting changes in the core-mantle boundary through the geological past.

Imaging the Earth's Interior

The new digital recording seismometers with broad wavelength sensitivity and large dynamic range include both portable varieties and permanent stations that will be applicable to global studies. The three-dimensional distribution of velocity anomalies in the mantle obtained through these data can then be used to infer relative temperatures and compositions within the mantle.

Experimental Determinations of Phase Equilibria and the Physical Properties of Earth Materials at High Pressure and Temperature

New high-pressure apparatus extends the range of experimentation. Properties of materials (e.g., density, seismic velocity, melting temperature) can be measured in situ using, for example, high-intensity x-rays produced by synchrotron sources. Comparison of the high-resolution seismic images of the interior with direct experimental determinations of the physical properties of earth materials at high-pressure and temperature will advance the understanding of the interior's temperature and compositional structure to an unprecedented degree. This can yield better insight into how the high-temperatures drive internal motions that in turn determine the geological history of the Earth's surface.

Chemical Geodynamics

The combination of geochemistry and geophysics continues to reveal the scale of heterogeneities within the mantle. Isotopic variations in mantle-derived rocks provide time-dependent information about the creation of mantle heterogeneities by partial melting or lithosphere subduction and about the efficiency of convection in remixing the mantle components. The nature and source of the mantle plumes responsible for generation of at least some volcanic hot-spots remain a tantalizing problem, one that may link phenomena at the core-mantle boundary to massive volcanic eruptions.

Geodynamic Modeling

The recent success in quantitatively relating geoid anomalies and the results of seismic tomography, at least on scales of thousands of kilometers, prompts similar investigations over smaller distances. The amount of material transported across the entire mantle by convection is currently the single largest uncertainty in our understanding of the Earth's thermal and geological evolution. This transport is part of the major geochemical cycles of the Earth.

FACILITIES, EQUIPMENT, AND DATA BASES

The earth sciences offer special opportunities for the development and application of new technologies, as exemplified by the instrumentation that has recently been created for use in the field and in the



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