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Start date: Feb 1, 2009, End date: Jan 31, 2015 PROJECT  FINISHED 

One of the major paradoxes in the geosciences is the contrast between the geochemical evidence for limited mass-exchange between lower and upper mantle, and the geophysical arguments for significant mass exchange, needed to prevent the mantle from melting in the geological past. Seismic tomography, when ultimately combined with geodynamical modeling, needs to provide estimates of present-day flux. Indeed, tomography has shown evidence for slabs penetrating into the lower mantle; but no quantitative information on the degree of mass exchange and heat flux can, as yet, reliably be obtained from tomographic images. It is crucial that the boundary between upper- and lower mantle be imaged at greater precision, certainly in the plume-rich southern hemisphere. This requires a combined effort of improvements both experimentally and theoretically. Much progress has recently been obtained by my group in Princeton before I returned to Europe. I propose to build upon those accomplishments, and to (1) Expand the data acquisition to the oceans by developing hydrophone-equipped floats, with the goal to improve data coverage in regions that are important to investigate heat flux: the plume-rich southern hemisphere in particular, (2) Combine different seismological data sets spanning a wide range of frequencies, with the goal to obtain tomographic images that allow for a quantitative estimate of heat flux (both upwards through plumes and downwards through the sinking of slab fragments), with emphasis on the boundary between upper- and lower mantle, (3) Exploit the extra resolution offered by the frequency-dependent sensitivity of body waves (multifrequency tomography), (4) Incorporate wavelet expansions into the tomographic inversion, with the aim to resolve more detail in the model where the data allow a higher resolution, (5) Obtain a multidisciplinary interpretation of new tomographic results through interaction with geodynamicists and geochemists.
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