The distribution of the ancient cratons (dark blue) around the world, revealed by cluster analysis of seismic shear-wave velocities in the upper mantle. White dots show where diamonds have been found on the surface, brought from the upper mantle by kimberlite volcanism. Credit: Garber et al., 2018, Figure 2, top left panel
Source: Geochemistry, Geophysics, Geosystems

High seismic velocities beneath cratons, the ancient cores of continents, indicate anomalous, depth-dependent composition of their lithosphere. What this composition is has been the subject of a long-standing controversy. Garber et al. [2018] compare profiles of seismic velocities from recent tomographic models with those computed for different lithospheric compositions and infer that the data can be explained by a ubiquitous presence of diamond and eclogite beneath cratons. They show that compositions with up to 2 percent of diamond and up to 20 percent eclogite can reproduce high seismic velocities observed at 120 to 150 kilometer depths. Such compositions are also consistent with various other geophysical observables, as well as data from natural samples and carbon mass balance constraints. Valued for their rarity at the Earth’s surface, diamonds may thus be plentiful at depth—surprisingly common building blocks of the deep lithosphere of cratons.

Citation: Garber, J. M., Maurya, S., Hernandez, J.‐A., Duncan, M. S., Zeng, L., Zhang, H. L., et al [2018]. Multidisciplinary constraints on the abundance of diamond and eclogite in the cratonic lithosphere. Geochemistry, Geophysics, Geosystems, 19.

—Sergei Lebedev, Associate Editor, Geochemistry, Geophysics, Geosystems

Text © 2018. The authors. CC BY-NC-ND 3.0
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